NEEDS AND WANTS

The five great lakes

2010-02-02T07:52:00.000-08:00

The Great Lakes are a collection of freshwater lakes located in eastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by surface.[1][2] They are sometimes referred to as the "Third Coast" by some citizens of the United States. Because of their size, types of ecosystems, and large abundances of beaches and coastal wetlands along their coasts, some regard them as inland seas or as one sea.[citation needed]

The Great Lakes hold 20% of the world's fresh water.[citation needed]

[edit] Geography
The Great Lakes region contains not only the five main lakes themselves, but also numerous minor lakes and rivers, as well as approximately 35,000 islands.

[edit] Bathymetry
Lake Erie Lake Huron Lake Michigan Lake Ontario Lake Superior
Surface area 9,940 sq mi (25,700 km2) 23,010 sq mi (59,600 km2) 22,400 sq mi (58,000 km2) 7,540 sq mi (19,500 km2) 31,820 sq mi (82,400 km2)
Water volume 116 cu mi (480 km3) 849 cu mi (3,540 km3) 1,180 cu mi (4,900 km3) 393 cu mi (1,640 km3) 2,900 cu mi (12,000 km3)
Elevation[3] 571 ft (174 m) 577 ft (176 m) 577 ft (176 m) 246 ft (75 m) 600 ft (180 m)
Average depth[4] 62 ft (19 m) 195 ft (59 m) 279 ft (85 m) 283 ft (86 m) 483 ft (147 m)
Maximum depth 210 ft (64 m) 770 ft (230 m) 923 ft (281 m) 808 ft (246 m) 1,332 ft (406 m)
Major settlements[5] Buffalo, NY
Cleveland, OH
Erie, PA
Toledo, OH Sarnia, ON
Owen Sound, ON
Alpena, MI
Port Huron, MI
Bay City, MI Chicago, IL
Gary, IN
Michigan City, IN
Muskegon, MI
Green Bay, WI
Milwaukee, WI Hamilton, ON
Kingston, ON
Oshawa, ON
Rochester, NY
Toronto, ON
Mississauga, ON Duluth, MN
Sault Ste. Marie, ON
Sault Ste. Marie, MI
Thunder Bay, ON
Marquette, MI
Superior, WI
Relative elevations, average depths, maximum depths, and volumes of the Great Lakes.

Notes: The area of each rectangle is proportionate to the volume of each lake. All measurements at Low Water Datum.
Source: EPA[3]

[edit] Lake Michigan-Huron
Lakes Michigan and Huron are hydrologically a single lake, sometimes called Lake Michigan-Huron; they have the same surface elevation of 577 feet (176 m),[6] and are connected not by a river but by the 295-foot (90 m) deep Straits of Mackinac.[4]

[edit] Rivers

Sarnia, ON, the largest city on Lake Huron, and the St. Clair River shoreline. The smokestacks of Chemical Valley along the river are visible in the background.The St. Marys River connects Lake Superior to Lake Huron.
The St. Clair River connects Lake Huron to Lake St. Clair.
The Detroit River connects Lake St. Clair to Lake Erie. Through its middle is the border between Canada and the United States.
The Niagara River, including Niagara Falls, connects Lake Erie to Lake Ontario.
The St. Lawrence River connects Lake Ontario to the Atlantic Ocean.
[edit] Other bodies of water
Georgian Bay is a large bay located within Lake Huron, separated by the Bruce Peninsula and Manitoulin Island. It contains the majority of the islands of the Great Lakes, with a count of approximately 30,000. The North Channel, a narrower westerly extension of Georgian Bay, separates Manitoulin Island from mainland Northern Ontario.
The Straits of Mackinac connects Lake Michigan to Lake Huron.
The Welland Canal connects Lake Erie to Lake Ontario, bypassing the Niagara River which cannot be fully navigated due to the presence of Niagara Falls.
Lake St. Clair is the smallest lake in the Great Lake system but due to its relatively small size (compared to the five "Great Lakes"), it is rarely, if ever, considered a Great Lake.
Lake Nipigon to the north of Lake Superior was formed by an extension or aulacogen of the Midcontinent Rift System which also formed Lake Superior, so the two lake beds are connected by shared geology. Lake Nipigon is sometimes called the sixth Great Lake.

The shoreline of a beach in the Apostle Islands, Lake Superior[edit] Islands
Dispersed throughout the Great Lakes are approximately 35,000 islands. The largest among them is Manitoulin Island in Lake Huron, the largest island in any inland body of water in the world. The second-largest island is Isle Royale in Lake Superior. Both of these islands are large enough to contain multiple lakes themselves — Manitoulin Island's Lake Manitou is listed in the Guinness Book of World Records as the world's largest lake located on a freshwater island.

[edit] Connection to ocean and open water
The Saint Lawrence Seaway and Great Lakes Waterway opened the Great Lakes to ocean-going vessels. The move to wider ocean-going container ships — which do not fit through the locks on these routes — has limited shipping on the lakes. Despite their vast size, large sections of the Great Lakes freeze over in winter, interrupting most shipping. Some icebreakers ply the lakes.

The Great Lakes are also connected to the Gulf of Mexico by way of the Illinois River (from Chicago) and the Mississippi River. An alternate track is via the Illinois River (from Chicago), to the Mississippi, up the Ohio, and then through the Tennessee-Tombigbee Waterway (combination of a series of rivers and lakes and canals), to Mobile Bay and the Gulf. Commercial tug-and-barge traffic on these waterways is heavy.

Pleasure boats can also enter or exit the Great Lakes by way of the Erie Canal and Hudson River in New York. The Erie Canal connects to the Great Lakes at the east end of Lake Erie (at Buffalo, NY) and at the south side of Lake Ontario (at Oswego, NY).

[edit] Boundaries
The lakes are bound by the Canadian province of Ontario and the U.S. states of Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania, and New York. However, not all of the lakes border on all of these regions. Four of the five lakes form part of the Canada-United States border; the fifth, Lake Michigan, is contained entirely within the United States. The Saint Lawrence River, which marks the same international border for a portion of its course, is the primary outlet of these interconnected lakes, and flows through Quebec and past the Gaspé Peninsula to the northern Atlantic Ocean.

[edit] Great Lakes Circle Tour
The Great Lakes Circle Tour is a designated scenic road system connecting all of the Great Lakes and the St. Lawrence River.[7]

[edit] Name origins
Lake Erie Lake Huron Lake Michigan Lake Ontario Lake Superior
Origins of Name Erie (tribe); shorten form of Iroquoian word Erielhonan or “long tail” Named by French explorers for inhabitants in the area, Wyandot or “Hurons” Likely from the Ojibwa word mishigami meaning “great water” Wyandot (Huron) word ontarío meaning “Lake of Shining Waters” (Ontara = beautiful, Ontario = beautiful lake) English translation of French term “lac supérieur” ("upper lake"), referring to its position above Lake Huron, Ojibwe called it "Gitchigumi"

[edit] Statistics
The Great Lakes contain roughly 22% of the world’s fresh surface water: 5,472 cubic miles (22,810 km3), or 6.0×1015 U.S. gallons (2.3×1016 liters). This is enough water to cover the 48 contiguous U.S. states to a uniform depth of 9.5 feet (2.9 m). However, only 2% of this volume is replaced each year, causing water levels to fall in recent years as the water undergoes heavy human use[citation needed]. Although the lakes contain a large percent of the world's fresh water, the Great Lakes supply only a small portion of America's drinking water (roughly 4.2%).[citation needed]

The combined surface area of the lakes is approximately 94,250 square miles (244,100 km2)—nearly the same size as the United Kingdom, and larger than the U.S. states of New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont and New Hampshire combined.

The Great Lakes coast measures approximately 10,500 miles (16,900 km);[4] however, the length of a coastline is impossible to measure exactly and is not a well-defined measure (see Coastline paradox).

[edit] Geology

A diagram of the formation of the Great Lakes.It has been estimated that the foundational geology which created the conditions shaping the present day upper Great Lakes was laid from 1.1 to 1.2 billion years ago,[4][8] when two previously fused tectonic plates split apart and created the Midcontinent Rift. A valley was formed providing a basin that eventually became modern day Lake Superior. When a second fault line, the Saint Lawrence rift, formed approximately 570 million years ago,[4] the basis for Lakes Ontario and Erie were created, along with what would become the St. Lawrence River.

The Great Lakes are estimated to have been formed at the end of the last ice age (about 10,000 years ago), when the Laurentide ice sheet receded. The retreat of the ice sheet left behind a large amount of meltwater (see Lake Agassiz) which filled up the basins that the glaciers had carved, thus creating the Great Lakes as we know them today.[9] Because of the uneven nature of glacier erosion, some higher hills became Great Lakes islands. The Niagara Escarpment follows the contour of the Great Lakes between New York and Wisconsin. Land below the glaciers "rebounded" as it was uncovered.[10] Because the glaciers covered some areas longer than others, this glacial rebound occurred at different rates. Some researchers believe that differential has contributed to fluctuating water levels throughout the Great Lakes basin.

[edit] Climate
[edit] Lake effect
The effect of Great Lakes on weather in the region is called the lake effect. In winter, the moisture picked up by the prevailing winds from the west can produce very heavy snowfall, especially along lake shores to the east such as Michigan, Ohio, Pennsylvania, Ontario, and New York. The lakes also moderate seasonal temperatures somewhat, by absorbing heat and cooling the air in summer, then slowly radiating that heat in autumn. This temperature buffering produces areas known as "fruit belts", where fruit typically grown farther south can be produced. Western Michigan has apple and cherry orchards, and vineyards adjacent to the lake shore as far north as the Grand Traverse Bay. The eastern shore of Lake Michigan and the southern shore of Lake Erie have many wineries as a result of this, as does the Niagara Peninsula between Lake Erie and Lake Ontario. A similar phenomenon occurs in the Finger Lakes region of New York as well as Prince Edward County, Ontario on Lake Ontario's northeast shore. Related to lake effect, is the occurrence of fog over medium-sized areas, particularly along the shorelines of the lakes. This is most noticeable along Lake Superior's shores, due to its maritime climate.

The Great Lakes have been observed to help strengthen storms, such as Hurricane Hazel in 1954, and a frontal system in 2007 that spawned a few tornadoes in Michigan and Ontario, picking up warmth from the lakes to fuel them. Also observed in 1996, was a rare subtropical cyclone forming in Lake Huron, dubbed the 1996 Lake Huron cyclone.

[edit] Economy
The lakes are extensively used for transport, though cargo traffic has decreased considerably in recent years. The Great Lakes Waterway makes each of the lakes accessible.

[edit] Historical economy

A woodcut of Le GriffonThe brigantine Le Griffon, which was commissioned by René Robert Cavelier, Sieur de La Salle, was built at Cayuga Creek, near the southern end of the Niagara River, and became the first sailing ship to travel the upper Great Lakes on August 7, 1679.

During settlement, the Great Lakes and its rivers were the only practical means of moving people and freight. Barges from middle North America were able to reach the Atlantic Ocean from the Great Lakes when the Erie Canal opened in 1825. By 1848, with the opening of the Illinois and Michigan Canal at Chicago, direct access to the Mississippi River was possible from the lakes. With these two canals an all-inland water route was provided between New York City and New Orleans.

The main business of many of the passenger lines in the 1800s was transporting immigrants. Many of the larger cities owe their existence to their position on the lakes as a freight destination as well as for being a magnet for immigrants. After railroads and surface roads developed, the freight and passenger businesses dwindled and, except for ferries and a few foreign cruise ships, has now vanished.

The immigration routes still have an effect today. Immigrants often formed their own communities and some areas have a pronounced ethnicity, such as Dutch, German, Polish, Finnish, and many others. Since many immigrants settled for a time in New England before moving westward, many areas on the U.S. side of the Great Lakes also have a New England feel, especially in home styles and accent.

Since general freight these days is transported by railroads and trucks, domestic ships mostly move bulk cargoes, such as iron ore, coal and limestone for the steel industry. The domestic bulk freight developed because of the nearby mines. It was more economical to transport the ingredients for steel to centralized plants rather than try to make steel on the spot. Ingredients for steel, however, are not the only bulk shipments made. Grain exports are also a major cargo on the lakes.

In the 19th and early 20th centuries, iron and other ores such as copper were shipped south on (downbound ships), and supplies, food, and coal were shipped north (upbound). Because of the location of the coal fields in Pennsylvania and West Virginia, and the general northeast track of the Appalachian Mountains, railroads naturally developed shipping routes that went due north to ports such as Erie, Pennsylvania and Ashtabula, Ohio.

Because the lake maritime community largely developed independently, it has some distinctive vocabulary. Ships, no matter the size, are called boats. When the sailing ships gave way to steamships, they were called steamboats—the same term used on the Mississippi. The ships also have a distinctive design (see Lake freighter). Ships that primarily trade on the lakes are known as lakers. Foreign boats are known as salties.

One of the more common sights on the lakes is the 1,000‑by‑105 foot (305-by-32 m), 78,850-long-ton (80,120-metric-ton) self-unloader. This is a laker with a conveyor belt system that can unload itself by swinging a crane over the side.[2] Today, the Great Lakes fleet is much smaller in numbers than it once was because of the increased use of overland freight, and a few larger ships replacing many small ones.

[edit] Modern economy
The Great Lakes are today used as a major mode of transport for bulk goods. In 2002, 162 million net tons of dry bulk cargo were moved on the Lakes. This was, in order of volume: iron ore, grain, and potash. The iron ore and much of the stone and coal are used in the steel industry. There is also some shipping of liquid and containerized cargo but most container ships cannot pass the locks on the Saint Lawrence Seaway because the ships are too wide. The total amount of shipping on the lakes has been on a downward trend for several years.

The Great Lakes are used to supply drinking water to tens of millions of people in bordering areas. This valuable resource is collectively administered by the state and provincial governments adjacent to the lakes.

Recreational boating and tourism are major industries on the Great Lakes. A few small cruise ships operate on the Great Lakes including a couple of sailing ships. Sport fishing, commercial fishing, and Native American fishing represent a US$4 billion a year industry with salmon, whitefish, smelt, lake trout, and walleye being major catches. In addition, all kinds of water sports can be found on the lakes. Unusually for inland waters, the Great Lakes proved the possibility of surfing, particularly in winter due to the effect of strong storms and waves.

[edit] Great Lakes Passenger Steamers
Main article: Great Lakes passenger steamers
From 1844 through 1857, palace steamers carried passengers and cargo around the Great Lakes. Throughout the 20th century, large luxurious passenger steamers sailed from Chicago all the way to Detroit and Cleveland. These were primarily operated by the Detroit & Cleveland Navigation Company. Several ferries currently operate on the Great Lakes to carry passengers to various islands, including Isle Royale, Pelee Island, Mackinac Island, Beaver Island, both Bois Blanc Islands, Kelleys Island, South Bass Island, North Manitou Island, South Manitou Island, Harsens Island, Manitoulin Island, and the Toronto Islands. As of 2007, three car ferry services cross the Great Lakes, two on Lake Michigan: a steamer from Ludington, Michigan to Manitowoc, Wisconsin and a high speed catamaran from Milwaukee to Muskegon, Michigan, and one on Lake Erie: a boat from Kingsville, Ontario, or Leamington, Ontario to Pelee Island, Ontario then onto Sandusky, Ohio. An international ferry across Lake Ontario from Rochester, New York to Toronto ran during 2004 and 2005, but is no longer in operation.

[edit] Some Passenger Steamers
Ship's Name Year Built Nationality Ship's Name Year Built Nationality Ship's Name Year Built Nationality
Niagara 1856 United States SS Christopher Columbus 1892 United States SS Eastland 1902 United States
Milwaukee Clipper 1904 United States SS Keewatin 1907 Canadian Comet (steamboat) 1857 United States

[edit] Shipwrecks
The large size of the Great Lakes increases the risk of water travel; storms and reefs are common threats. The lakes are prone to sudden and severe storms, particularly in the autumn, from late October until early December. Hundreds of ships have met their end on the lakes. The greatest concentration of shipwrecks lies near Thunder Bay (Michigan), beneath Lake Huron, near the point where eastbound and westbound shipping lanes converge.

The Lake Superior shipwreck coast from Grand Marais, Michigan to Whitefish Point became known as the "Graveyard of the Great Lakes". More vessels have been lost in the Whitefish Point area than any other part of Lake Superior.[11] The Whitefish Point Underwater Preserve serves as an underwater museum to protect the many shipwrecks in this area.

The first shipwreck was the Griffin, the first ship to sail the Great Lakes. Caught in a storm while trading furs between Green Bay and Michilimacinac, it sank during a storm[12] and has possibly been found.[13] The last major freighter wrecked on the lakes was the SS Edmund Fitzgerald, which sank on November 10, 1975, just over 30 miles (50 km) offshore from Whitefish Point. The largest loss of life in a shipwreck out on the lakes may have been that of the Lady Elgin, wrecked in 1860 with the loss of around 400 lives. In an incident at a Chicago dock in 1915, the SS Eastland rolled over while loading passengers, killing 841.

In August 2007, the Great Lakes Shipwreck Historical Society announced that it had found the wreckage of Cyprus, a 420-foot (130 m) long, century-old ore carrier. Cyprus sank during a Lake Superior storm on October 11, 1907, during its second voyage while hauling iron ore from Superior, Wisconsin, to Buffalo, New York. The entire crew of 23 drowned, except one, a man named Charles Pitz, who floated on a life raft for almost seven hours.[14]

In June 2008 deep sea divers in Lake Ontario found the wreck of the 1780 Royal Navy warship HMS Ontario in what has been described as an "archaeological miracle".[15] There are no plans to raise her as the site is being treated as a war grave.

[edit] See also
Category:Shipwrecks in the Great Lakes
List of Great Lakes shipwrecks
Great Storms of the North American Great Lakes
Great Lakes Storm of 1913
Mataafa Storm of 1905
Michigan Underwater Preserves
Thunder Bay National Marine Sanctuary

[edit] Political issues and legislation
[edit] Great Lakes water use and diversions
The International Joint Commission was established in 1909 to help prevent and resolve disputes relating to the use and quality of boundary waters, and to advise Canada and the United States on questions related to water resources. Concerns over diversion of Lake water are of concern to both Americans and Canadians. Some water is diverted through the Chicago River to operate the Illinois Waterway but the flow is limited by treaty. Possible schemes for bottled water plants and diversion to dry regions of the continent raise concerns. Under the U.S. "Water Resources Development Act"[3], diversion of water from the Great Lakes Basin requires the approval of all eight Great Lakes governors through the Great Lakes Commission, which rarely occurs. International treaties regulate large diversions. In 1998, the Canadian company Nova Group won approval from the Province of Ontario to withdraw 158,000,000 US gallons (600,000 m3) of Lake Superior water annually to ship by tanker to Asian countries. Public outcry forced the company to abandon the plan before it began. Since that time, the eight Great Lakes Governors and the Premiers of Ontario and Quebec have negotiated the Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement [4] and the Great Lakes-St. Lawrence River Basin Water Resources Compact [5] that would prevent most future diversion proposals and all long-distance ones. The agreements also strengthen protection against abusive water withdrawal practices within the Great Lakes basin. On December 13, 2005, the Governors and Premiers signed these two agreements, the first of which is between all ten jurisdictions. It is somewhat more detailed and protective, though its legal strength has not yet been tested in court. The second, the Great Lakes Compact, has been approved by the state legislatures of all eight states that border the Great Lakes as well as the U.S. Congress, and was signed into law by President George W. Bush on 3 October 2008.[16]

[edit] Coast Guard live fire exercises
In 2006, the United States Coast Guard (USCG) proposed a plan to designate 34 areas in the Great Lakes, at least five miles (8 km) offshore, as permanent safety zones for live fire machine gun practice. In August 2006 the plan was published in the Federal Register. The USCG reserved the right to hold target practice whenever the weather allowed with a two hour notice. These firing ranges would be open to the public when not in use. In response to requests from the public, the Coast Guard held a series of public meetings in nine U.S. cities to solicit comment. During these meetings many people voiced concerns about the plan and its impact on the environment.[17]

A preliminary health risk assessment stated that the "proposed training will result in no elevated risks for a freshwater system such as the Great Lakes using 'realistic worst case' assumptions, and further investigation is not recommended ... if typical rather than worst case assumptions were used, the predicted risk would be even less."[18] However, the assessment was based on lead levels after five years, and so one could infer that lead levels could meet or exceed EPA safe levels for lead after fifteen years.[19] The Coast Guard established an information page about their proposal at http://www.uscgd9safetyzones.com

On December 18, 2006, the Coast Guard announced its decision to withdraw the entire proposal.[20] Officials said they would look into alternative ammunition, modifying the proposed zones and have more public dialogue before proposing a new plan.[21]

[edit] Great Lakes Collaboration Implementation Act
During the 109th United States Congress in 2006, the Great Lakes Collaboration Implementation Act (Bill HR5100) was introduced to enact the recommendations of the Great Lakes Regional Collaboration, an effort established in 2004 to produce a strategy for restoring and maintaining the Great Lakes. The bill was introduced by U.S. senators Mike DeWine and Carl Levin, along with representatives Vern Ehlers and Rahm Emanuel.

The bill states that "the Great Lakes are on the brink of an ecologic catastrophe" and that "if the pattern of deterioration is not reversed immediately, the damage could be irreparable". It cites the closing of over 1,800 beaches in 2003, the 6,300-square-mile (16,300 km2) dead zone in Lake Erie, and the US$500 million damage each year due to the zebra mussel as evidences that "a comprehensive restoration of the system is needed to prevent the Great Lakes from collapsing".[22]

A press release states that the bill aims to stop the introduction and spreading of invasive species, prevent the Asian carp from invading the Great Lakes, phase out mercury, restore animal habitats, and prevent sewage contamination.[23]

A coalition called Healing Our Waters,or HOW was formed by several environmental groups and foundations in 2005 to educate and assist citizens in advocating for the cleanup of the Great Lakes.

[edit] Additions to the five Great Lakes
Lake Champlain, a lake on the border between upstate New York and northwestern Vermont that is part of the Saint Lawrence-Great Lakes Watershed, briefly became labeled by the U.S. government as the sixth "Great Lake of the United States" on March 6, 1998, when President Clinton signed Senate Bill 927. This bill, which reauthorized the National Sea Grant Program, contained a line penned by Senator Patrick Leahy (D-VT) declaring Lake Champlain to be a Great Lake. Not coincidentally, this status allows neighboring states to apply for additional federal research and education funds allocated to these national resources. The claim was viewed with some amusement by other countries, particularly in the Canadian media, and the lake is small compared to other Canadian lakes (such as Great Bear Lake which has over 27 times more surface area). Following a small uproar (and several New York Times and Time Magazine[24] articles), the Great Lake status was rescinded on March 24, 1998 (although Vermont universities continue to receive funds to monitor and study the lake).

Similarly, there has been interest in making Lake St. Clair a Great Lake. In October 2002, backers planned to present such a proposal at the Great Lakes Commission annual meeting[25], but ultimately withheld it as it appeared to them to have too little support.[26]

[edit] Ecology
[edit] Ecological challenges
The ecological history of the Great Lakes includes both great losses and enormous recovery; the system today is in the most-obvious ways much healthier than it was a half-century ago, while in less-apparent ways it remains seriously compromised.

Before the arrival of Europeans, the Great Lakes provided fish to the indigenous groups who lived near them. Early European settlers were astounded by both the variety and quantity of fishes; there were 150 different species in the Great Lakes[4]. Historically, fish populations were the early indicator of the condition of the Lakes, and have remained one of the key indicators even in the current era of sophisticated analyses and measuring instruments. According to the bi-national (U.S. and Canadian) resource book, The Great Lakes: An Environmental Atlas and Resource Book, "the largest Great Lakes fish harvests were recorded in 1889 and 1899 at some 67,000 tonnes [147 million pounds]," though the beginning of environmental impacts on the fish can be traced back nearly a century prior to those years.

By 1801, the New York Legislature found it necessary to pass regulations curtailing obstructions to the natural migrations of Atlantic salmon from Lake Erie into their spawning channels. In the early nineteenth century, Upper Canada's government found it necessary to introduce similar legislation prohibiting the use of weirs and nets at the mouths of Lake Ontario’s tributaries. Other protective legislation was passed as well, but enforcement remained difficult and often quite spotty.

On both sides of the Canada–United States border, the proliferation of dams and impoundments multiplied, necessitating more regulatory efforts. The decline in fish populations was unmistakable by the middle of the nineteenth century, as the obstructions in the rivers prevented salmon and sturgeon from reaching their spawning grounds. The decline in salmon was recognized by Canadian officials and reported as virtually a complete absence by the end of the 1860s. The Wisconsin Fisheries Commission noted a reduction of roughly 25 percent in general fish harvests by 1875. Many Michigan rivers sport multiple dams that range from mere relics to those with serious loss of life potential. The state's dam removal budget has been frozen in recent years; in the 1990s, the state was removing 1 dam per year.

Overfishing was cited as responsible for the decline of the population of various whitefish, important because of their culinary desirability and, hence, economic consequence. Moreover, between 1879 and 1899, reported whitefish harvests declined from some 24.3 million pounds (11 million kg) to just over 9 million pounds (4 million kg). Recorded sturgeon catches fell from 7.8 million pounds (1.5 million kg) in 1879 to 1.7 million pounds (770,000 kg) in 1899. The population of giant freshwater mussels was eliminated as the mussels were harvested for use as buttons by early Great Lakes entrepreneurs.

There were, however, other factors in the population declines besides overfishing and the problems posed by water obstructions. Logging in the Great Lakes region removed tree cover near stream channels which provide spawning grounds, and this affected necessary shade and temperature-moderating conditions. Removal of tree cover also destabilized soil, allowing soil to be carried in greater quantity into the streambeds, and even brought about more frequent flooding. Running cut logs down the Lakes’ tributary rivers also stirred bottom sediments. In 1884, the New York Fish Commission determined that the dumping of sawmill waste (chips and sawdust) was impacting fish populations.

In the development of ecological problems in the Great Lakes, it was the influx of parasitic lamprey populations after the development of the Erie Canal and the much later Welland Canal that led to the two federal governments attempting to work together. Despite a variety of efforts to eliminate or minimize the lamprey, by the mid 1950s the lake trout populations of Lakes Michigan and Huron were reduced by about 99%, with the lamprey deemed largely to blame. This led to the launch of the bi-national Great Lakes Fishery Commission.

Other ecological problems in the Lakes and their surroundings have stemmed from urban runoff and sprawl, sewage disposal, and toxic industrial effluent. These, of course, also affect aquatic food chains and fish populations. Some of these glaring problem areas are what attracted the high-level publicity of Great Lakes ecological troubles in the 1960s and 1970s. Evidence of chemical pollution in the Lakes and their tributaries now stretches back for decades. In the 1960s Ohio’s Cuyahoga River -- or more precisely a combination of oil, chemicals, and trash floating atop it in Cleveland—ignited and smoldered, creating international headlines.

The Cuyahoga, and a TIME Magazine cover story about the "death" of Lake Erie, helped focus public and policymaker attention and inspire the first Earth Day events in 1970. New advocacy organizations such as the Lake Michigan Federation, founded in 1970 by Lee Botts, brought new public pressure to bear. The first U.S. Clean Water Act, signed by President Richard Nixon in 1972, was a key step forward as was the innovative[27] bi-national Great Lakes Water Quality Agreement signed by Canada and the U.S. Thanks to a variety of steps taken to reduce industrial and municipal pollution discharges into the system, basic water quality had by the 1980s improved sharply and Lake Erie in particular was significantly healthier. The ongoing discharge of toxic substances has also been sharply reduced thanks to federal and state bans of substances like PCBs and DDT, though historic toxics remain embedded in harbor and rivermouth sediments in dozens of "Great Lakes Areas of Concern".

The authoritative but now outdated 1972 book The Great Lakes: An Environmental Atlas and Resource Book noted that "only pockets remain of the once large commercial fishery." In the meanwhile however the great water quality improvements realized during the 1970s and 1980s, combined with successful salmonid stocking programs, have enabled the growth of a large recreational fishery.

[edit] Invasive species
Since the 1800s an estimated 160 species have invaded the Great Lakes ecosystem, with ship ballast being a primary suspected pathway[28], causing severe economic and ecological impacts.[29] According to the Inland Seas Education Association, on average a new invasive species enters the Great Lakes every eight months.[29]

A zebra mussel-encrusted Vector Averaging Current Meter from Lake Michigan.One such infestation in the Great Lakes was the introduction of the zebra mussel, which was first discovered in 1988.[30] The mollusk is an efficient feeder, competing with native mussels. It also reduces available food and spawning grounds for fish. The zebra mussel also hurts utility and manufacturing industries by clogging or blocking pipes. The U.S. Fish and Wildlife Service estimates that the economic impact of the zebra mussel will be about $5 billion over the next decade.[31]

The alewife first entered the system west of Lake Ontario via 19th-century canals. By the 1960s the small silver fish had become a familiar nuisance to beachgoers across lakes Michigan, Huron and Erie as periodic mass dieoffs resulted in vast numbers of them washing up on shore; estimates by various governments have placed the percentage of Lake Michigan's biomass which was made up of alewives in the early 1960s as high as 90 percent. The various state and federal governments began stocking several species of salmonids in the late 1960s, including the native lake trout as well as non-native chinook and coho salmon; by the 1980s alewife populations had dropped drastically. Ironically, today the sharply lower numbers of alewives is seen as a problem[6] by those involved in the large recreational fishing sector that has grown up particularly on Lake Michigan.

The ruffe, a small percid fish, became the most abundant fish species in Lake Superior's St. Louis River within five years of its detection in 1986. Its range, which has expanded to Lake Huron, poses a significant threat to the lower lake fishery. Five years after first being observed in the St. Clair River, the round goby can now be found in all of the Great Lakes. The goby is considered undesirable for several reasons: It preys upon bottom-feeding fish, overruns optimal habitat, spawns multiple times a season, and can survive poor water quality conditions.[32]

Several species of water fleas have accidentally been introduced into the Great lakes such as Bythotrephes cederstroemi and the Fishhook waterflea potentially having an effect on the zooplankton population. Several species of crayfish have also been introduced that may contend with native crayfish populations. More recently an electric fence has been set up across the Chicago Sanitary and Ship Canal in order to keep several species of invasive Asian carps out of the area. These fast-growing planktivorous fish have heavily colonized the Mississippi and Illinois river systems. [7]

It has been suggested that invasive species, particularly zebra and quagga mussels, may be at least partially responsible for the collapse of the deepwater demersal fish community in Lake Huron[33] as well as drastic unprecedented changes in the zooplankton community of the lake[34].

Amazon rainforest

2010-01-23T20:21:00.001-08:00

The Amazon rainforest (Brazilian Portuguese: Floresta Amazônica or Amazônia; Spanish: Selva Amazónica or Amazonia), also known as Amazonia, or the Amazon jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America. This basin encompasses seven million square kilometers (1.7 billion acres), of which five and a half million square kilometers (1.4 billion acres) are covered by the rainforest. This region includes territory belonging to nine nations. The majority of the forest is contained within Brazil, with 60% of the rainforest, followed by Peru with 13%, and with minor amounts in Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname, and French Guiana. States or departments in four nations bear the name Amazonas after it. The Amazon represents over half of the planet's remaining rainforests, and it comprises the largest and most species-rich tract of tropical rainforest in the world.

The Amazon rainforest was short-listed in 2008 as a candidate to one of the New7Wonders of Nature by the New Seven Wonders of the World Foundation. As of February 2009 the Amazon was ranking first in Group E, the category for forests, national parks and nature reserves.

Etymology
The name Amazon is said to arise from a war which Francisco de Orellana had with a tribe of Tapuyas and other tribes from South America. The women of the tribe fought alongside the men, as was the custom among the entire tribe.[2] Orellana's descriptions may have been accurate, but a few historians speculate that Orellana could have been mistaking indigenous men wearing "grass skirts" for women.[citation needed] Orellana derived the name Amazonas from the ancient Amazons of Asia and Africa described by Herodotus and Diodorus in Greek legends.[2]

Another etymology for the word suggests that it came originally from a native word amazona (Spanish spelling) or amassona (Portuguese spelling), meaning "destroyer (of) boats", in reference to the destructive nature of the root system possessed by some riparian plants.

History

Earth during the EoceneThe rainforest likely formed during the Eocene era, following the evolutionary appearance of angiosperm plants. It appeared following a global reduction of tropical temperatures when the Atlantic Ocean had widened sufficiently to provide a warm, moist climate to the Amazon basin. The rain forest has been in existence for at least 55 million years, and most of the region remained free of savanna-type biomes during that time period.[3][4]

Following the Cretaceous–Tertiary extinction event, the extinction of the dinosaurs and the wetter climate may have allowed the tropical rainforest to spread out across the continent. From 65–34 Mya, the rainforest extended as far south as 45°. Climate fluctuations during the last 34 million years have allowed savanna regions to expand into the tropics. During the Oligocene, for example, the rainforest spanned a relatively narrow band that lay mostly above latitude 15°N. It expanded again during the Middle Miocene, then retracted to a mostly inland formation at the last glacial maximum.[5] However, the rainforest still managed to thrive during these glacial periods, allowing for the survival and evolution of a broad diversity of species.[6]

During the mid-Eocene, it is believed that the drainage basin of the Amazon was split along the middle of the continent by the Purus Arch. Water on the eastern side flowed toward the Atlantic, while to the west water flowed toward the Pacific across the Amazonas Basin. As the Andes Mountains rose, however, a large basin was created that enclosed a lake; now known as the Solimões Basin. Within the last 5–10 million years, this accumulating water broke through the Purus Arch, joining the easterly flow toward the Atlantic.[7][8]

There is evidence that there have been significant changes in Amazon rainforest vegetation over the last 21,000 years through the Last Glacial Maximum (LGM) and subsequent deglaciation. Analyses of sediment deposits from Amazon basin paleolakes and from the Amazon Fan indicate that rainfall in the basin during the LGM was lower than for the present, and this was almost certainly associated with reduced moist tropical vegetation cover in the basin.[9] There is debate, however, over how extensive this reduction was. Some scientists argue that the rainforest was reduced to small, isolated refugia separated by open forest and grassland;[10] other scientists argue that the rainforest remained largely intact but extended less far to the north, south, and east than is seen today.[11] This debate has proved difficult to resolve because the practical limitations of working in the rainforest mean that data sampling is biased away from the center of the Amazon basin, and both explanations are reasonably well supported by the available data.

Based on archaeological evidence from an excavation at Caverna da Pedra Pintada, human inhabitants first settled in the Amazon region at least 11,200 years ago.[12] Subsequent development led to late-prehistoric settlements along the periphery of the forest by 1250 CE, which induced alterations in the forest cover.[13] Biologists believe that a population density of 0.2 persons/km2 is the maximum that can be sustained in the rain forest through hunting. Hence, agriculture is needed to host a larger population.[14] The first European to travel the length of the Amazon River was Francisco de Orellana in 1542.[15]

Biodiversity

Deforestation in the Amazon Rainforest threatens many species of tree frogs, which are very sensitive to environmental changes (pictured: Giant leaf frog)
Scarlet Macaw, which is indigenous to the American tropics.Wet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than the wet forests in Africa and Asia.[16] As the largest tract of tropical rainforest in the Americas, the Amazonian rainforests have unparalleled biodiversity. One in ten known species in the world live in the Amazon Rainforest.[17] This constitutes the largest collection of living plants and animal species in the world.

The region is home to about 2.5 million insect species,[18] tens of thousands of plants, and some 2,000 birds and mammals. To date, at least 40,000 plant species, 3,000 fish, 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically classified in the region.[19] One in five of all the birds in the world live in the rainforests of the Amazon. Scientists have described between 96,660 and 128,843 invertebrate species in Brazil alone.[20]

The diversity of plant species is the highest on Earth with some experts estimating that one square kilometer may contain over 75,000 types of trees and 150,000 species of higher plants. One square kilometer of Amazon rainforest can contain about 90,790 tonnes of living plants. The average plant biomass is estimated at 356 ± 47 tonnes ha−1.[21] To date, an estimated 438,000 species of plants of economic and social interest have been registered in the region with many more remaining to be discovered or catalogued.[22]

The green leaf area of plants and trees in the rainforest varies by about 25% as a result of seasonal changes. Leaves expand during the dry season when sunlight is at a maximum, then undergo abscission in the cloudy wet season. These changes provide a balance of carbon between photosynthesis and respiration.[23]

The rainforest contains several species that can pose a hazard. Among the largest predatory creatures are the Black Caiman, Jaguar and Anaconda. In the river, electric eels can produce an electric shock that can stun or kill, while Piranha are known to bite and injure humans.[24] Various species of poison dart frogs secrete lipophilic alkaloid toxins through their flesh. There are also numerous parasites and disease vectors. Vampire bats dwell in the rainforest and can spread the rabies virus.[25] Malaria, yellow fever and Dengue fever can also be contracted in the Amazon region.

Deforestation
Main article: Deforestation of the Amazon Rainforest
Deforestation is the conversion of forested areas to non-forested areas. The main sources of deforestation in the Amazon are human settlement and development of the land.[26] Prior to the early 1960s, access to the forest's interior was highly restricted, and the forest remained basically intact.[27] Farms established during the 1960s was based on crop cultivation and the slash and burn method. However, the colonists were unable to manage their fields and the crops because of the loss of soil fertility and weed invasion.[28] The soils in the Amazon are productive for just a short period of time, so farmers are constantly moving to new areas and clearing more land.[28] These farming practices led to deforestation and caused extensive environmental damage.[29] Deforestation is considerable, and areas cleared of forest are visible to the naked eye from outer space.

Between 1991 and 2000, the total area of forest lost in the Amazon rose from 415,000 to 587,000 km2, with most of the lost forest becoming pasture for cattle.[30] Seventy percent of formerly forested land in the Amazon, and 91% of land deforested since 1970, is used for livestock pasture.[31][32] In addition, Brazil is currently the second-largest global producer of soybeans after the United States. The needs of soy farmers have been used to validate many of the controversial transportation projects that are currently developing in the Amazon. The first two highways successfully opened up the rain forest and led to increased settlement and deforestation. The mean annual deforestation rate from 2000 to 2005 (22,392 km2 per year) was 18% higher than in the previous five years (19,018 km2 per year).[33] At the current rate, in two decades the Amazon Rainforest will be reduced by 40%.[34]

NASA satellite observation of deforestation in the Mato Grosso state of Brazil. The transformation from forest to farm is evident by the paler square shaped areas under development.

Fires and Deforestation in the state of Rondônia.

One consequence of forest clearing in the Amazon: thick smoke that hangs over the forest.

Conservation and climate change
See also: Gaviotas
Environmentalists are concerned about the loss of biodiversity which will result from destruction of the forest, and also about the release of the carbon contained within the vegetation, which could accelerate global warming. Amazonian evergreen forests account for about 10% of the world's terrestrial primary productivity and 10% of the carbon stores in ecosystems[35]—of the order of 1.1 × 1011 metric tonnes of carbon.[36] Amazonian forests are estimated to have accumulated 0.62 ± 0.37 tons of carbon per hectare per year between 1975 and 1996.[36]

One computer model of future climate change caused by greenhouse gas emissions shows that the Amazon rainforest could become unsustainable under conditions of severely reduced rainfall and increased temperatures, leading to an almost complete loss of rainforest cover in the basin by 2100.[37][38] However, simulations of Amazon basin climate change across many different models are not consistent in their estimation of any rainfall response, ranging from weak increases to strong decreases.[39] The result indicates that the rainforest could be threatened though the 21st century by climate change in addition to deforestation.

In 1989, environmentalist C.M. Peters and two colleagues stated there is economic as well as biological incentive to protecting the rainforest. One hectare in the Peruvian Amazon has been calculated to have a value of $6820 if intact forest is sustainably harvested for fruits, latex, and timber; $1000 if clear-cut for commercial timber (not sustainably harvested); or $148 if used as cattle pasture.[40]

As indigenous territories continue to be destroyed by deforestation and ecocide, such as in the Peruvian Amazon[41] indigenous peoples' rainforest communities continue to disappear, while others, like the Urarina continue to struggle to fight for their cultural survival and the fate of their forested territories. Meanwhile, the relationship between nonhuman primates in the subsistence and symbolism of indigenous lowland South American peoples has gained increased attention, as has ethno-biology and community-based conservation efforts.

From 2002 to 2006, the conserved land in the Amazon Rainforest has almost tripled and deforestation rates have dropped up to 60%. About 1,000,000 square kilometres (250,000,000 acres) have been put onto some sort of conservation, which adds up to a current amount of 1,730,000 square kilometres (430,000,000 acres).[42]

Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.

Aerosols over the Amazon each September for four burning seasons (2005 through 2008). The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.

Aerial roots of red mangrove on an Amazonian river.

Remote sensing

This image reveals how the forest and the atmosphere interact to create a uniform layer of “popcorn” clouds.The use of remotely sensed data is dramatically improving conservationists' knowledge of the Amazon Basin. Given the objectivity and lowered costs of satellite-based land cover analysis, it appears likely that remote sensing technology will be an integral part of assessing the extent and damage of deforestation in the basin.[43] Furthermore, remote sensing is the best and perhaps only possible way to study the Amazon on a large-scale.[44]

The use of remote sensing for the conservation of the Amazon is also being used by the indigenous tribes of the basin to protect their tribal lands from commercial interests. Using handheld GPS devices and programs like Google Earth, members of the Trio Tribe, who live in the rainforests of southern Suriname, map out their ancestral lands to help strengthen their territorial claims.[45] Currently, most tribes in the Amazon do not have clearly defined boundaries, which make their territories easy targets for commercial poaching of natural resources. Through the use of cheap mapping technology, the Trio Tribe hopes to protect its ancestral land.

In order to accurately map the biomass of the Amazon and subsequent carbon related emissions, the classification of tree growth stages within different parts of the forest is crucial. In 2006 Tatiana Kuplich organized the trees of the Amazon into four categories: (1) mature forest, (2) regenerating forest [less than three years], (3) regenerating forest [between three and five years of regrowth], and (4) regenerating forest [eleven to eighteen years of continued development].[46] The researcher used a combination of Synthetic aperture radar (SAR) and Thematic Mapper (TM) to accurately place the different portions of the Amazon into one of the four classifications.

Impact of Amazon drought
In 2005, parts of the Amazon basin experienced the worst drought in 100 years,[47] and there were indications that 2006 could have been a second successive year of drought.[48] A 23 July 2006 article in the UK newspaper The Independent reported Woods Hole Research Center results showing that the forest in its present form could survive only three years of drought.[49][50] Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a "tipping point" where it would irreversibly start to die. It concludes that the forest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate.

According to the World Wide Fund for Nature, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.[51]

Road Rules

2009-10-27T08:44:00.000-07:00

Road Rules, MTV's second reality show, debuted on July 19, 1995. The series followed six strangers between the ages of 18 and 24 (five strangers in the first four seasons) after stripping them of their money and putting them on an RV traveling from location to location only guided by a set of clues and a mission to complete at each location. It was nominated for an Emmy Award in 2001.

The ground-breaking series was a pioneer in travel/adventure/reward reality television (together with Mark Burnett's Eco-Challenge productions). Road Rules was created by Jonathan Murray and Mary-Ellis Bunim of Bunim/Murray Productions. After Bunim died of cancer in early 2004, the show went on hiatus for three years. After season 14 ended, it has been confirmed that Road Rules is no longer in production, although MTV nor Bunim-Murray have commented on the status of the series.[citation needed]

The show was spawned from its sister show The Real World. The idea of Road Rules came to mind, when Real World castmates Jon, Tami and Dominic traveled in an RV across the United States to get to their The Real World: Los Angeles house in the first two episodes of the second season. Bunim-Murray began working on the show soon after the third San Francisco season, and finally debuted in 1995. The show garnered a spin-off series, Real World/Road Rules Challenge, which is still in production.

There was also a 1998 mini-series, Road Rules: All-Stars, in which five former stars from The Real World go on a short Road Rules course managed by infamous former Real World housemate Puck, who, until the very end of the series, was disguising his identity with the alias "Mr. Big". However, this is generally considered the first season of Real World/Road Rules Challenge.

Contents [hide]
1 Seasons
2 Show's evolution
2.1 Europe (Season 3)
2.2 Islands (Season 4)
2.3 Northern Trail (Season 5)
2.4 Down Under (Season 6)
2.5 Latin America(Season 7)
2.6 Semester at Sea (Season 8)
2.7 Maximum Velocity Tour (Season 9)
2.8 The Quest (Season 10)
3 Road Rules face-offs
4 External links

[edit] Seasons
Season Year Cast members Handsome Reward
1 USA - The First Adventure 1995 Allison Jones Kit Hoover Los Jackson Mark Long Shelly Spottedhorse N/A European Trip
2 USA - The Second Adventure 1996 Emily Bailey Tim Beggy Christian Breivik Devin Elston Effie Perez N/A Honda Civics
3 Europe 1997 Patrice Boudibela Antoine de Bouverie Elizabeth "Belou" Den Tex Chris Melling Michelle Parma N/A Home entertainment center and $1000 cash
4 Islands 1997 Jake Bronstein Kalle Dedolph Vincent Forcier Oscar Hernandez Erika Ruen N/A Enrollment and Tuition on Semester at Sea Program
5 Northern Trail 1998 Jon Holmes Roni Martin Tara McDaniel Dan Setzler Noah Rickun Anne Wharton Trip to Greece
6 Down Under 1998 Susie Meister Chadwick Pelletier Shayne McBride Christina Pazsitzky Kefla Hare Piggy Thomas Choice of Seadoo, Motorbike or Harley
7 Latin America 1999 Brian Lancaster Sarah Martinez Gladys Sanabria Josh Florence Holly Shand Abe Ingersoll Volkswagen Beetle
8 Semester at Sea 1999 Veronica Portillo Yes Duffy Pua Medieros Pawel Litwinski Ayanna Mackins Shawn Sealy iMac Desktop Computer Package
9 Maximum Velocity Tour 2000 Laterrian Wallace Kathryn Kolb Holly Brentson James Orlando Msaada Nia Theo Vonkurnatowski Cumulative Cash Prize on Cobalt Credit Card
10 The Quest 2001 Jisela Delgado Sophia Pasquis Adam Larson Blair Herter Steve Meinke Ellen Cho Suzuki Grand Vitaras
*Katie Doyle
11 Campus Crawl 2002 Kendal Sheppard Shane Landrum Rachel Robinson Darrell Taylor Sarah Greyson Eric Jones Trip around the World
*Raquel Duran
12 South Pacific 2003 Cara Zavaleta Dave Giuntoli Christena Pyle Abram Boise Mary Beth Decker Donell Langham Car
*Tina Barta *Chris Graebe *Jeremy Blossom
13 X-Treme 2004 Jodi Weatherton Danny Dias Kina Dean Derrick Kosinski Ibis Nieves Patrick Maloney Subaru WRXI
*Nick Haggart *Angela Trimbur *Jillian Zoboroski
14 Viewers' Revenge 2007 Abram Boise Kina Dean Shane Landrum Adam Larson Susie Meister Veronica Portillo Mazda3 and Cumulative Cash Prize
*Dan Walsh *David Leech *Angel Turlington *Tori Hall
*Derek McCray *Dan Walsh *Susie Meister
*LaMonte Ponder

[edit] Show's evolution
The series began with a simple format, closely mirroring its parent show The Real World. The concept was simple, abandon five strangers on the road, take away their money, have them drive around in an RV completing missions and doing odd jobs for money, and if they lasted to the end of the trip, they would win a "handsome reward". It was touted as The Real World on an RV, but as the show progressed, several changes were made to the show for various reasons, mostly having to do with causing excitement and raising sagging ratings.

[edit] Europe (Season 3)
In its third season, producers of the show took production to the next level by deciding to move the show from the United States to Europe. While the first two seasons were not themed according to the series' location, the third season introduced the subtitle into the concept which would usually strand the Roadies in different locations around the world.

[edit] Islands (Season 4)
For the first time, the RV was completely abandoned for a short time in favor of an alternate mode of transportation. The cast traveled in and around the Caribbean islands and for a short time traveled on a catamaran. This season also competed against the Boston season of the Real World in San Juan, Puerto Rico, planting the seeds for The Real World/Road Rules Challenge and future face-offs.

[edit] Northern Trail (Season 5)
Changing the dynamic of the cast in hopes of creating more drama by including more people in the RV, an additional cast member would be included in each season, changing the number of cast members from five to six. Jon is considered the "stand out" of the season. With his zany antics and half-baked notions of romantic hijinks, he became both one of the most loved and conversely despised characters in the show's history.

[edit] Down Under (Season 6)
[edit] Latin America(Season 7)
[edit] Semester at Sea (Season 8)
Enticed by the idea of sailing around the world, producers put the cast on the (for 2005) University of Pittsburgh's Semester at Sea educational program. For the first time in any season, in order for the cast to get their handsome reward, the cast needed to complete coursework aboard the ship. Prior to this, cast members only needed to get to the end of the trip, and would not be penalized for refusing to do a mission. The most unusual mission was "Anime Mission", visiting Japan and experiencing ADR recording by their voices with Japanese director, Yuji Moriya who was center in the anime industry in the USA at that time.

[edit] Maximum Velocity Tour (Season 9)
Due to an exaggerated trend of sagging ratings, some say due to the Semester at Sea season, the show underwent a major re-tooling. The Maximum Velocity Tour represents when the series transitioned from a documentary-style reality show to an entertainment reality show. The show was brought back to the US and given a "game show" format. At the helm of a trip was a fictional character named the "Road Master" completed. After the cast would complete a mission, they would have money added to the group pool and if they failed to complete a mission, they would lose the money.

[edit] The Quest (Season 10)
Producers continued to re-tool the show. This time, if the cast members lost two missions, they would have to vote out a cast member. Any additional mission lost after that, another cast member would be voted off. Also, instead of adding money to a group pool, the cast competed each mission for a "key" to the handsome reward. The "keys" were placed in the RV on a large board where each "key" represented a virtue the cast learned in that mission. For this season, the "key" would be represented as part of a crest. If the cast lost a mission, they would not receive the "key" until they voted off a cast member. Jisela Delgado was the first cast member to be voted off in the series. Katie Doyle was the first replacement in the series. The series remained largely unchanged after this season, although each subsequent series had its own variation on the rules of the game.

Sunny Pundai Oussari Thevudaiyanmavan

[edit] Road Rules face-offs
Setting up the idea for Real World/Road Rules Challenge, the face-offs have come to be an instrumental part of each season. The current cast competes either with a current "The Real World" cast who would be filming their series parallel to theirs or a former Road Rules cast, if Real World was ever out of its production season. The first official face-off, between the Islands and Boston casts gained such high ratings, that another spin-off series was begun, the ever-popular Challenges, and a pattern in every season where the cast would compete against another cast for a separate prize.

First Adventure - No face-off during this season. Although cast member Mark initially appeared on the Real World: San Francisco season as one of three possible replacements for ousted housemate, Puck. The housemates chose Jo over Mark.
Second Adventure vs. Real World Miami - The Road Rules cast posed as house cleaners and stole the Miami's cast eight-ball. They did so successfully. Timmy fooled Miami's Dan and Cynthia who were obviously suspicious of the unannounced cleaning crew.
Europe - No face-off.
Islands vs. Real World Boston - The casts competed in a series of competitions in San Juan, Puerto Rico. The Boston cast narrowly won the games. Syrus, while competing in the final mission, busted his shin on a bench for his team to take the prize. The Islands crew, who desperately needed money at that time asked the Boston cast to split their winnings. The Boston cast declined to do so. They also played paintball with a team of former Road Rulers from different seasons.
Northern Trail vs. Road Rules All-Stars - The casts competed in a series of Olympic-themed games including luge, ski jumping, and figure skating. The Olympic-theme was due in part to the fact that the casts were competing in the Olympic facilities at Lake Placid, New York. The All-Stars won the competition in the figure skating competition. The Northern Trail handed the keys off to their RV, which the All-Stars cast used for their season.
Down Under vs. Real World Seattle - The cast competed in the "Aqua Games" in Seattle's main harbor. They competed in various games, including holding onto the back of a raft attached to a seadoo, jumping into rings from a platform, and the finale: a bull-riding contest. Nathan won the competition for the Seattle cast, while Christina and Susie both took the competition as a joke.
Latin America vs. Road Rules Down Under - The cast competed in Veracruz, Mexico in a series of games. The Down Under cast took the prize, but the more serious implication of this face-off was when Abe of the Latin America cast hooked up with Susie in the RV. This started the tension between Abe and Gladys, which led to Gladys hitting Abe and being sent home.
Semester at Sea - Did not do a face-off. However, during the filming and airing of the series, rumors were rampant that the two casts met up in India, where The Real World Hawaii took their vacation and the Semester at Sea cast landed in port. This was never confirmed or denied. Various students on the Semester at Sea program participated in various missions during this season.
Maximum Velocity Tour vs. Real World New Orleans - In a throwback to the very first face-off, the Maximum Velocity Tour cast worked with a Make-A-Wish child to pull off a sting on the Real World: New Orleans cast. They included the Make-A-Wish child in the mission, as the cast posed as Make-A-Wish ambassadors to distract the cast members while James and Laterrian jumped a back wall to steal the New Orleans' cast robotic dog. Hearing that the cast was in town, Melissa of the New Orleans cast hid the eight-ball in anticipation of the cast stealing it. This cast also competed in Los Angeles, CA against the cast of the first season of Making the Band (O-Town) in which O-Town won. They also competed against a group of winners from an MTV.com contest in Provo, Utah, which Road Rules won.
The Quest vs. Real World Back to New York - The casts met up in Morocco. These two casts met up after spending a week in Palm Spring during casting. Members of each cast had already made friends and enemies, creating instant drama and the casts playing practical jokes on each other. In direct contrast to her competitive persona on the Challenges, Back to New York's Coral and fellow cast member Nicole refused to compete in a mud wrestling challenge. This left Back to New York's Lori and Rachel to compete alone against the Road Rules girls. In a grueling mud wrestling competition, Road Rules won because Coral and Nicole refused to compete.
Campus Crawl vs. Real World Las Vegas - The Campus Crawl cast first had to take a photograph with one of the Las Vegas cast members handcuffed to the bathtub. Because Raquel had met Steven of Las Vegas in the College Station casting call, Raquel was able to coax Steven to show her and Rachel the Las Vegas suite. Not knowing that the two were from Road Rules, they were able to handcuff and photograph Steven. The cast competed at Lake Red Rock near Las Vegas, Nevada which The Real World won.
South Pacific vs. Road Rules Campus Crawl - This cast competed in a marathon challenge, in which the cast was required to compete in different games but were not allowed to sleep during the 48-hour period. In the last competition, in which they had to remember various details in the past 48 hours, the Campus Crawl cast pulled off a win.
X-treme vs. Road Rules South Pacific - The two casts competed in a series of games which concludes with a boxing match. The X-treme cast beat the South Pacific cast.
Viewers' Revenge vs. Pit Crew. Roadies beat out the Pit Crew in a mission that had players carrying tires from sand dunes. They also beat the Pit Crew in a mission that involved weight lifting and weight puzzles, along with a football game. The final challenge was carrying boxes across semis and dropping them into the hole; Pit Crew finally won, making the score 3-1.

The Earth

2009-10-24T08:53:00.001-07:00

Earth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets (non-gas planets) in the Solar System in terms of diameter, mass and density. It is also referred to as the World, the Blue Planet,[note 3] and Terra.[note 4]

Home to millions of species,[11] including humans, Earth is the only place in the universe where life is known to exist. The planet formed 4.54 billion years ago,[12] and life appeared on its surface within a billion years. Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful radiation, permitting life on land.[13] The physical properties of the Earth, as well as its geological history and orbit, allowed life to persist during this period. The world is expected to continue supporting life for another 1.5 billion years, after which the rising luminosity of the Sun will eliminate the biosphere.[14]

Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and islands; liquid water, necessary for all known life, is not known to exist on any other planet's surface.[note 5][note 6] Earth's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.

Earth interacts with other objects in outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days.[note 7] The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane,[15] producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. Between approximately 4.1 and 3.8 billion years ago, asteroid impacts during the Late Heavy Bombardment caused significant changes to the surface environment.

Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. The inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in Earth being the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.

Contents [hide]
1 Chronology
1.1 Evolution of life
1.2 Future
2 Composition and structure
2.1 Shape
2.2 Chemical composition
2.3 Internal structure
2.4 Heat
2.5 Tectonic plates
2.6 Surface
2.7 Hydrosphere
2.8 Atmosphere
2.8.1 Weather and climate
2.8.2 Upper atmosphere
2.9 Magnetic field
3 Orbit and rotation
3.1 Rotation
3.2 Orbit
3.3 Axial tilt and seasons
4 Moon
5 Habitability
5.1 Biosphere
5.2 Natural resources and land use
5.3 Natural and environmental hazards
5.4 Human geography
6 Cultural viewpoint
7 See also
8 Notes
9 References
10 Bibliography
11 External links

Chronology
Main article: History of the Earth
See also: Geological history of Earth
Scientists have been able to reconstruct detailed information about the planet's past. The earliest dated solar system material is dated to 4.5672 ± 0.0006 billion years ago,[16] and by 4.54 billion years ago (within an uncertainty of 1%)[12] the Earth and the other planets in the Solar System formed out of the solar nebula—a disk-shaped mass of dust and gas left over from the formation of the Sun. This assembly of the Earth through accretion was largely completed within 10–20 million years.[17] Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed shortly thereafter, 4.53 billion years ago,[18] most likely as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass[19] impacting the Earth in a glancing blow.[20] Some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.

Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans.[21] The newly-formed Sun was only 70% of its present luminosity, yet evidence shows that the early oceans remained liquid—a contradiction dubbed the faint young Sun paradox. A combination of greenhouse gases and higher levels of solar activity served to raise the Earth's surface temperature, preventing the oceans from freezing over.[22]

Two major models have been proposed for the rate of continental growth:[23] steady growth to the present-day[24] and rapid growth early in Earth history.[25] Current research shows that the second option is most likely, with rapid initial growth of continental crust[26] followed by a long-term steady continental area.[27][28][29] On time scales lasting hundreds of millions of years, the surface continually reshaped itself as continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (Ma), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma, then finally Pangaea, which broke apart 180 Ma.[30]

Evolution of life
Main article: Evolutionary history of life
At present, Earth provides the only example of an environment that has given rise to the evolution of life.[31] Highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed.[32] The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed in a layer of ozone (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.[33] True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth.[34]

Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 Ma, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.[35]

Following the Cambrian explosion, about 535 Ma, there have been five mass extinctions.[36] The last extinction event was 65 Ma, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several million years ago, an African ape-like animal such as orrorin tugenensis gained the ability to stand upright.[37] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,[38] affecting both the nature and quantity of other life forms.

The present pattern of ice ages began about 40 Ma and then intensified during the Pleistocene about 3 Ma. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago.[39]

Future
Main article: Future of the Earth
See also: Risks to civilization, humans and planet Earth

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.[40] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans.[41]

The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to lethal levels for plants (10 ppm for C4 photosynthesis) in 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.[42] After another billion years all surface water will have disappeared[14] and the mean global temperature will reach 70 °C[42](158 °F). The Earth is expected to be effectively habitable for about another 500 million years,[43] although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere.[44] Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO2 due to reduced volcanism,[45] and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.[46]

The Sun, as part of its evolution, will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU (150,000,000 km).[40][47] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. Therefore, the planet is expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life will be destroyed because of the Sun's increased luminosity.[40] However, a more recent simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be destroyed.[47]

Composition and structure
Main article: Earth science
Further information: Earth physical characteristics tables
Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity, the strongest magnetic field, and fastest rotation.[48] It also is the only terrestrial planet with active plate tectonics.[49]

Shape
Main article: Figure of the Earth

Size comparison of inner planets (left to right): Mercury, Venus, Earth and MarsThe shape of the Earth is very close to that of an oblate spheroid, a sphere squished along the orientation from pole to pole such that there is a bulge around the equator.[50] This bulge results from the rotation of the Earth, and causes the diameter at the equator to be 43 km larger than the pole to pole diameter.[51] The average diameter of the reference spheroid is about 12,742 km, which is approximately 40,000 km/π, as the meter was originally defined as 1/10,000,000 of the distance from the equator to the North Pole through Paris, France.[52]

Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.[53] The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Because of the equatorial bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador.[54][55]

Chemical Composition of the Crust[56] Compound Formula Composition
Continental Oceanic
silica SiO2 60.2% 48.6%
alumina Al2O3 15.2% 16.5%
lime CaO 5.5% 12.3%
magnesia MgO 3.1% 6.8%
iron(II) oxide FeO 3.8% 6.2%
sodium oxide Na2O 3.0% 2.6%
potassium oxide K2O 2.8% 0.4%
iron(III) oxide Fe2O3 2.5% 2.3%
water H2O 1.4% 1.1%
carbon dioxide CO2 1.2% 1.4%
titanium dioxide TiO2 0.7% 1.4%
phosphorus pentoxide P2O5 0.2% 0.3%
Total 99.6% 99.9%
Chemical composition
See also: Abundance of elements on Earth
The mass of the Earth is approximately 5.98 × 1024 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.[57]

The geochemist F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99.22% were composed of 11 oxides (see the table at right.) All the other constituents occur only in very small quantities.[note 8]

Internal structure
Main article: Structure of the Earth
The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer of the Earth is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity, and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are comprised. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 kilometers below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core.[58] The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year.[59]

Geologic layers of the Earth[60]
Earth cutaway from core to exosphere. Not to scale. Depth[61]
km Component Layer Density
g/cm3
0–60 Lithosphere[note 9] —
0–35 ... Crust[note 10] 2.2–2.9
35–60 ... Upper mantle 3.4–4.4
35–2890 Mantle 3.4–5.6
100–700 ... Asthenosphere —
2890–5100 Outer core 9.9–12.2
5100–6378 Inner core 12.8–13.1

Heat
Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).[62] The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[63] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.[64] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 billion years ago,[62] would have increased temperature gradients within the Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today.[65]

Present-day major heat-producing isotopes[66] Isotope Heat release
W/kg isotope Half-life

years Mean mantle concentration
kg isotope/kg mantle Heat release
W/kg mantle
238U 9.46 × 10-5 4.47 × 109 30.8 × 10-9 2.91 × 10-12
235U 5.69 × 10-4 7.04 × 108 0.22 × 10-9 1.25 × 10-13
232Th 2.64 × 10-5 1.40 × 1010 124 × 10-9 3.27 × 10-12
40K 2.92 × 10-5 1.25 × 109 36.9 × 10-9 1.08 × 10-12

Total heat loss from the earth is 4.2 × 1013 Watts.[67] A portion of the core's thermal energy is transported toward the crust by Mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.[68] More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, majority of which occurs in the oceans due to the crust there being much thinner than that of the continents.[67]

Tectonic plates
Earth's main plates[69]
Plate name Area
106 km²
African Plate[note 11] 78.0
Antarctic Plate 60.9
Australian Plate 47.2
Eurasian Plate 67.8
North American Plate 75.9
South American Plate 43.6
Pacific Plate 103.3
Main article: Plate tectonics
The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: Convergent boundaries, at which two plates come together, Divergent boundaries, at which two plates are pulled apart, and Transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.[70] The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates,[71] and their motion is strongly coupled with patterns convection inside the Earth's mantle.

As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes continually recycles the oceanic crust back into the mantle. Because of this recycling, most of the ocean floor is less than 100 million years in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about 200 million years.[72][73] By comparison, the oldest dated continental crust is 4030 million years old.[74]

Other notable plates include the Indian Plate, the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate actually fused with Indian Plate between 50 and 55 million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/yr[75] and the Pacific Plate moving 52–69 mm/yr. At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21 mm/yr.[76]

Surface
Main articles: Landform and Extreme points of Earth
The Earth's terrain varies greatly from place to place. About 70.8%[77] of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes,[51] oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining 29.2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies.

The planetary surface undergoes reshaping over geological time periods due to the effects of tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts[78] also act to reshape the landscape.

Present day Earth altimetry and bathymetry. Data from the National Geophysical Data Center's TerrainBase Digital Terrain Model.The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors.[79] Sedimentary rock is formed from the accumulation of sediment that becomes compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust.[80] The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz, the feldspars, amphibole, mica, pyroxene and olivine.[81] Common carbonate minerals include calcite (found in limestone), aragonite and dolomite.[82]

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. Currently the total arable land is 13.31% of the land surface, with only 4.71% supporting permanent crops.[7] Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1.3 × 107 km² of cropland and 3.4 × 107 km² of pastureland.[83]

The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The mean height of land above sea level is 840 m.[84]

Hydrosphere
Main article: Hydrosphere

Elevation histogram of the surface of the Earth. Approximately 71% of the Earth's surface is covered with water.The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the Solar System. The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of −10,911.4 m.[note 12][85] The average depth of the oceans is 3,800 m, more than four times the average height of the continents.[84]

The mass of the oceans is approximately 1.35 × 1018 metric tons, or about 1/4400 of the total mass of the Earth, and occupies a volume of 1.386 × 109 km3. If all of the land on Earth were spread evenly, water would rise to an altitude of more than 2.7 km.[note 13] About 97.5% of the water is saline, while the remaining 2.5% is fresh water. The majority of the fresh water, about 68.7%, is currently in the form of ice.[86]

About 3.5% of the total mass of the oceans consists of salt. Most of this salt was released from volcanic activity or extracted from cool, igneous rocks.[87] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.[88] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.[89] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation.[90]

Atmosphere
Main article: Earth's atmosphere
The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km.[8] It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation due to weather and seasonal factors.[91]

Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 billion years ago, forming the primarily nitrogen-oxygen atmosphere that exists today. This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life on Earth include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[92] This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Carbon dioxide, water vapor, methane and ozone are the primary greenhouse gases in the Earth's atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C and life would likely not exist.[77]

Weather and climate
Main articles: Weather and Climate
The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km of the planet's surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospheric circulation that drives the weather and climate through redistribution of heat energy.[93]

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.[94] Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes heat energy from the equatorial oceans to the polar regions.[95]

Source regions of global air massesWater vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as precipitation.[93] Most of the water is then transported back to lower elevations by river systems, usually returning to the oceans or being deposited into lakes. This water cycle is a vital mechanism for supporting life on land, and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topological features and temperature differences determine the average precipitation that falls in each region.[96]

The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.[97] Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. The commonly used Köppen climate classification system (as modified by Wladimir Köppen's student Rudolph Geiger) has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.[94]

Upper atmosphere

This view from orbit shows the full Moon partially obscured by the Earth's atmosphere. NASA image.See also: Outer space
Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere.[92] Each of these layers has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere. This is where the Earth's magnetic fields interact with the solar wind.[98] An important part of the atmosphere for life on Earth is the ozone layer, a component of the stratosphere that partially shields the surface from ultraviolet light. The Kármán line, defined as 100 km above the Earth's surface, is a working definition for the boundary between atmosphere and space.[99]

Due to thermal energy, some of the molecules at the outer edge of the Earth's atmosphere have their velocity increased to the point where they can escape from the planet's gravity. This results in a slow but steady leakage of the atmosphere into space. Because unfixed hydrogen has a low molecular weight, it can achieve escape velocity more readily and it leaks into outer space at a greater rate than other gasses.[100] The leakage of hydrogen into space is a contributing factor in pushing the Earth from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is believed to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.[101] Hence the ability of hydrogen to escape from the Earth's atmosphere may have influenced the nature of life that developed on the planet.[102] In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.[103]

Magnetic field

The Earth's magnetic field, which approximates a dipole.Main article: Earth's magnetic field
The Earth's magnetic field is shaped roughly as a magnetic dipole, with the poles currently located proximate to the planet's geographic poles. According to dynamo theory, the field is generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. These in turn produce the Earth's magnetic field. The convection movements in the core are chaotic in nature, and periodically change alignment. This results in field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.[104][105]

The field forms the magnetosphere, which deflects particles in the solar wind. The sunward edge of the bow shock is located at about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the Van Allen radiation belts, a pair of concentric, torus-shaped regions of energetic charged particles. When the plasma enters the Earth's atmosphere at the magnetic poles, it forms the aurora.[106]

Orbit and rotation
Rotation
Main article: Earth's rotation

Earth's axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit.Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time. Each of these seconds is slightly longer than an SI second because Earth's solar day is now slightly longer than it was during the 19th century due to tidal acceleration.[107]

Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86164.098903691 seconds of mean solar time (UT1), or 23h 56m 4.098903691s. [108][note 14] Earth's rotation period relative to the precessing or moving mean vernal equinox, misnamed its sidereal day, is 86164.09053083288 seconds of mean solar time (UT1) (23h 56m 4.09053083288s).[108] Thus the sidereal day is shorter than the stellar day by about 8.4 ms.[109] The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005[110] and 1962–2005.[111]

Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. This is equivalent to an apparent diameter of the Sun or Moon every two minutes; the apparent sizes of the Sun and the Moon are approximately the same.[112][113]

Orbit
Main article: Earth's orbit
Earth orbits the Sun at an average distance of about 150 million kilometers every 365.2564 mean solar days, or one sidereal year. From Earth, this gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, or a Sun or Moon diameter every 12 hours. Because of this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of the Earth averages about 30 km/s (108,000 km/h), which is fast enough to cover the planet's diameter (about 12,600 km) in seven minutes, and the distance to the Moon (384,000 km) in four hours.[8]

The Moon revolves with the Earth around a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common revolution around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon and their axial rotations are all counter-clockwise. Viewed from a vantage point above the north poles of both the Sun and the Earth, the Earth appears to revolve in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.5 degrees from the perpendicular to the Earth–Sun plane, and the Earth–Moon plane is tilted about 5 degrees against the Earth-Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.[8][114]

The Hill sphere, or gravitational sphere of influence, of the Earth is about 1.5 Gm (or 1,500,000 kilometers) in radius.[115][note 15] This is maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.

Illustration of the Milky Way Galaxy, showing the location of the Sun.Earth, along with the Solar System, is situated in the Milky Way galaxy, orbiting about 28,000 light years from the center of the galaxy. It is currently about 20 light years above the galaxy's equatorial plane in the Orion spiral arm.[116]

Axial tilt and seasons
Main article: Axial tilt
Because of the axial tilt of the Earth, the amount of sunlight reaching any given point on the surface varies over the course of the year. This results in seasonal change in climate, with summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun, and winter taking place when the pole is pointed away. During the summer, the day lasts longer and the Sun climbs higher in the sky. In winter, the climate becomes generally cooler and the days shorter. Above the Arctic Circle, an extreme case is reached where there is no daylight at all for part of the year—a polar night. In the southern hemisphere the situation is exactly reversed, with the South Pole oriented opposite the direction of the North Pole.

Earth and Moon from Mars, imaged by Mars Global Surveyor. From space, the Earth can be seen to go through phases similar to the phases of the Moon.By astronomical convention, the four seasons are determined by the solstices—the point in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when the direction of the tilt and the direction to the Sun are perpendicular. Winter solstice occurs on about December 21, summer solstice is near June 21, spring equinox is around March 20 and autumnal equinox is about September 23.[117]

The angle of the Earth's tilt is relatively stable over long periods of time. However, the tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles also migrate a few meters across the surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. The rotational velocity of the Earth also varies in a phenomenon known as length of day variation.[118]

In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4. However, these dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth-Sun distance results in an increase of about 6.9%[119] in solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere.[120]

Moon
Characteristics Diameter 3,474.8 km
2,159.2 mi
Mass 7.349 × 1022 kg
8.1 × 1019 (short) tons
Semi-major axis 384,400 km
238,700 mi
Orbital period 27 d 7 h 43.7 m
Main article: Moon
The Moon is a relatively large, terrestrial, planet-like satellite, with a diameter about one-quarter of the Earth's. It is the largest moon in the Solar System relative to the size of its planet. (Charon is larger relative to the dwarf planet Pluto.) The natural satellites orbiting other planets are called "moons" after Earth's Moon.

The gravitational attraction between the Earth and Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases; the dark part of the face is separated from the light part by the solar terminator.

Because of their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm a year. Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs a year—add up to significant changes.[121] During the Devonian period, for example, (approximately 410 million years ago) there were 400 days in a year, with each day lasting 21.8 hours.[122]

The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon.[123] Some theorists believe that without this stabilization against the torques applied by the Sun and planets to the Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting chaotic changes over millions of years, as appears to be the case for Mars.[124] If Earth's axis of rotation were to approach the plane of the ecliptic, extremely severe weather could result from the resulting extreme seasonal differences. One pole would be pointed directly toward the Sun during summer and directly away during winter. Planetary scientists who have studied the effect claim that this might kill all large animal and higher plant life.[125] However, this is a controversial subject, and further studies of Mars—which has a similar rotation period and axial tilt as Earth, but not its large Moon or liquid core—may settle the matter.

Viewed from Earth, the Moon is just far enough away to have very nearly the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant.[113] This allows total and annular eclipses to occur on Earth.

A scale representation of the relative sizes of, and distance between, Earth and Moon.
The most widely accepted theory of the Moon's origin, the giant impact theory, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust.[126]

Earth has at least two co-orbital asteroids, 3753 Cruithne and 2002 AA29.[127]

Habitability
See also: Planetary habitability

A range of theoretical habitable zones with stars of different mass (our Solar System at center). Not to scale.A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides the (currently understood) requisite conditions of liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain metabolism.[128] The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the conditions necessary to originate and sustain life on this planet.[129]

Biosphere
Main article: Biosphere
The planet's life forms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion years ago. Earth is the only place in the universe where life is known to exist. Some scientists believe that Earth-like biospheres might be rare.[130]

The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land primarily latitude and height above the sea level separates biomes. Terrestrial biomes lying within the Arctic, Antarctic Circle or in high altitudes are relatively barren of plant and animal life, while the greatest latitudinal diversity of species is found at the Equator.[131]

Natural resources and land use
Main article: Natural resource
The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.

Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics.[132] These bodies form concentrated sources for many metals and other useful elements.

The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[133] Humans also live on the land by using building materials to construct shelters. In 1993, human use of land is approximately:

Land use Percentage
Arable land 13.13%[7]
Permanent crops 4.71%[7]
Permanent pastures 26%
Forests and woodland 32%
Urban areas 1.5%
Other 30%

The estimated amount of irrigated land in 1993 was 2,481,250 km².[7]

Natural and environmental hazards
Large areas are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other calamities and disasters.

Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species.

A scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather conditions and a global rise in average sea levels.[134]

Human geography
Main article: Human geography
See also: World

Cartography, the study and practice of map making, and vicariously geography, have historically been the disciplines devoted to depicting the Earth. Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.

Earth has approximately 6,740,000,000 human inhabitants as of November 2008.[135] Projections indicate that the world's human population will reach seven billion in 2013 and 9.2 billion in 2050.[136] Most of the growth is expected to take place in developing nations. Human population density varies widely around the world, but a majority live in Asia. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.[137]

It is estimated that only one eighth of the surface of the Earth is suitable for humans to live on—three-quarters is covered by oceans, and half of the land area is either desert (14%),[138] high mountains (27%),[139] or other less suitable terrain. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada.[140] (82°28′N) The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole. (90°S)

The Earth at night, a composite of DMSP/OLS ground illumination data on a simulated night-time image of the world. This image is not photographic and many features are brighter than they would appear to a direct observer.Independent sovereign nations claim the planet's entire land surface, with the exception of some parts of Antarctica. As of 2007 there are 201 sovereign states, including the 192 United Nations member states. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities.[7] Historically, Earth has never had a sovereign government with authority over the entire globe, although a number of nation-states have striven for world domination and failed.[141]

The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.[142] It is not, however, a world government. While the U.N. provides a mechanism for international law and, when the consensus of the membership permits, armed intervention,[143] it serves primarily as a forum for international diplomacy.

The first human to orbit the Earth was Yuri Gagarin on April 12, 1961.[144] In total, about 400 people visited outer space and reached Earth orbit as of 2004, and, of these, twelve have walked on the Moon.[145][146][147] Normally the only humans in space are those on the International Space Station. The station's crew, currently six people, is usually replaced every six months.[148] Humans traveled the farthest from the planet in 1970, when Apollo 13 crew was 400,171 km away from Earth.[149][150]

Cultural viewpoint
Main article: Earth in culture

The first photograph ever taken by astronauts of an "Earthrise", from Apollo 8The name "Earth" was derived from the Anglo-Saxon word erda, which means ground or soil. It became eorthe in Old English, then erthe in Middle English.[151] The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle.[152]

Earth has often been personified as a deity, in particular a goddess. In many cultures the mother goddess, also called the Mother Earth, is also portrayed as a fertility deity. Creation myths in many religions recall a story involving the creation of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with fundamentalist branches of Protestantism[153] or Islam,[154] assert that their interpretations of these creation myths in sacred texts are literal truth and should be considered alongside or replace conventional scientific accounts of the formation of the Earth and the origin and development of life.[155] Such assertions are opposed by the scientific community[156][157] and other religious groups.[158][159][160] A prominent example is the creation-evolution controversy.

In the past there were varying levels of belief in a flat Earth,[161] but this was displaced by the concept of a spherical Earth due to observation and circumnavigation.[162] The human perspective regarding the Earth has changed following the advent of spaceflight, and the biosphere is now widely viewed from a globally integrated perspective.[163][164] This is reflected in a growing environmental movement that is concerned about humankind's effects on the planet

What is peace?

2009-10-24T08:47:00.000-07:00

Peace has always been among humanity's highest values--for some, supreme. Consider: "Peace at any price."1 "The most disadvantageous peace is better than the most just war."2 "Peace is more important than all justice."3 "I prefer the most unjust peace to the justest war that was ever waged."4 "There never was a good war or a bad peace."5
Yet, we agree little on what is peace. Perhaps the most popular (Western) view is as an absence of dissension, violence, or war, a meaning found in the New Testament and possibly an original meaning of the Greek word for peace, Irene. Pacifists have adopted this interpretation, for to them all violence is bad. This meaning is widely accepted among irenologists6 and students of international relations. It is the primary dictionary definition.

Peace, however, is also seen as concord, or harmony and tranquility. It is viewed as peace of mind or serenity, especially in the East. It is defined as a state of law or civil government, a state of justice or goodness, a balance or equilibrium of Powers.

Such meanings of peace function at different levels. Peace may be opposed to or an opposite of antagonistic conflict, violence, or war. It may refer to an internal state (of mind or of nations) or to external relations. Or it may be narrow in conception, referring to specific relations in a particular situation (like a peace treaty), or overarching, covering a whole society (as in a world peace). Peace may be a dichotomy (it exists or it does not) or continuous, passive or active, empirical or abstract, descriptive or normative, or positive or negative.

The problem is, of course, that peace derives its meaning and qualities within a theory or framework. Christian, Hindu, or Buddhist will see peace differently, as will pacifist or internationalist. Socialist, fascist, and libertarian have different perspectives, as do power or idealistic theorists of international relations. In this diversity of meanings, peace is no different from such concepts as justice, freedom, equality, power, conflict, class, and, indeed, any other concept.

All concepts are defined within a theory or cognitive framework--what I have called elsewhere a perspective.7 Through a perspective peace is endowed with meaning by being linked to other concepts within a particular perception of reality; and by its relationship to ideas or assumptions about violence, history, divine grace, justice. Peace is thereby locked into a descriptive or explanatory view of our reality and each other.

My perspective, which sees peace as a phase in a conflict helix, an equilibrium within a social field, has been presented in the previous four volumes.7a In this Chapter I will review this perspective, make clear the imbedded meaning of peace, describe its related qualities and dimensions, and prepare for considering alternative conceptualizations in the next Chapter. This and Chapter 3 are thus the prologue to my subsequent theory of a just peace.

2.2 PEACE AS A SOCIAL CONTRACT
My perspective and associated meaning of peace are best summarized through a number of social principles. These have been documented and the evidence given for them elsewhere,8 as will be noted for each.

2.2.1 The Conflict Principle
Conflict is a balancing of powers among interests, capabilities, and wills.9 It is a mutual adjusting of what people want, can get, and are willing to pursue. Conflict behavior, whether hostile actions, violence, or war, is then a means and manifestation of this process.

2.2.2 The Cooperation Principle
Cooperation depends on expectations aligned with power. Through conflict in a specific situation, a balance of powers and associated agreement are achieved. This balance is a definite equilibrium among the parties' interests, capabilities, and wills; the agreement is a simultaneous solution to the different equations of power, and thereby the achievement of a certain harmony--structure--of expectations. At the core of this structure is a status quo, or particular expectations over rights and obligations. Conflict thus interfaces and interlocks a specific balance of powers and an associated structure of expectations.

Cooperation--contractual or familistic interactions10--depends on a harmony of expectations, a mutual ability of the parties to predict the outcome of their behavior. Such is, for example, the major value of a written contract or treaty. And this structure of expectations depends on a particular balance of powers.11 Thus, cooperation depends on expectations aligned with power.

2.2.3 The Gap Principle
A gap between expectations and power causes conflict. A structure of expectations, once established, has considerable social inertia, while the supporting balance of powers can change rapidly. Interests can shift, new capabilities can develop, wills can strengthen or weaken. As the underlying balance of powers changes, a gap between power and the structure of expectations can form, causing the associated agreement to lose support. The larger this gap, the greater the tension toward revising expectations in line with the change in power, and thus the more likely some random event will trigger conflict over the associated interests. Such conflict then serves to create a new congruence between expectations and power.

Conflict and cooperation therefore are interdependent. They are alternative phases in a continuous social process12 underlying human interaction: now conflict, then cooperation, and then again conflict.13 Cooperation involves a harmony of expectations congruent with a balance of powers achieved by conflict.

2.2.4 The Helix Principle
Conflict becomes less intense, cooperation14 more lasting. If interaction occurs in a closed system or is free from sudden, sharp changes in the conditions of a relationship (as, for example, if one party to a business contract goes bankrupt, or a signatory to a regional military alliance with the United States has a military coup), then through conflict and cooperation people gradually learn more about each other, their mutual adjustments come easier, their expectations more harmonious and lasting. Conflict and cooperation thus form a helix, moving upward on a curve of learning and adjustments, with the turn through cooperation being more familistic and durable; that through conflict shorter and less intense.15

2.2.5 The Second and Fourth Master Principles
Through conflict is negotiated a social contract.16 As mentioned, conflict is a balancing of powers--a conscious or subconscious negotiation of opposing interests, capabilities, and wills. This process determines some implicit or explicit, subconscious or conscious social contract. It is social in involving a relationship or interaction between two or more wills. It is a contract in that there is an agreement--a harmonization of expectations.
It is this social contract that is peace within social field theory. Peace, then is determined by a process of adjustment between what people, groups, or states want, can, and will do. Peace is based on a consequent balance of powers and involves a corresponding structure of expectations and patterns of cooperation. Moreover, peace may become unstable when an increasing gap develops between expectations and power, as here defined,17 and may collapse into conflict, violence, or war.

2.3 THE NATURE OF A SOCIAL CONTRACT
Social contracts, the structural basis of peace as here defined, take many forms that interconnect and overlap in diverse, complex ways to order social communities and organizations. I can hardly engage here this variety, which would itself require a volume.18 Rather, I shall simply outline the diversity of social contracts, especially so that the nested, overlapping, and multilayered nature of social contracts, and thus peace, is clear.
Throughout the following discussion three points should be kept in mind. First, as mentioned, a social contract is the outcome of parties balancing their mutual interests, capabilities, and wills, and is based on a particular balance thus achieved--a balance of powers.

Second, the powers constituting the balance are not necessarily coercive or authoritative; threat or legitimacy are not the only bases for social contracts. Altruistic, intellectual, or exchange powers (based on love, persuasion, or promises, respectively) may dominate. Thus, a social contract may be a marriage agreement, an understanding developed among scientists over a disputed theory, or a sale in a market.19

Third, a social contract--this peace--is only a phase in a conflict helix and is thus a temporary equilibrium in the long-term movement of interpersonal, social, or international relations.

2.3.1 Expectations
As used here, an expectation is a prediction about the outcome of one's behavior.20 A social contract harmonizes certain expectations between the parties; that is, it enables each to reliably predict the other's responses. Such expectations are varied; our vocabulary for discriminating among them is well developed. Remembering my fundamental concern with social peace and conflict (and thus I am uninterested in, for example, a legal classification of contracts), these can be divided into status quo and non-status quo expectations. Within these two divisions I can define five types, as shown in Table 2.1.

A. Status quo. The concept of status quo is basic to these volumes. In previous volumes21 I argued that a breakdown of status quo expectations is a necessary cause of violence and war, and I tried to verify this against empirical results.22 The reason for this necessity is that status quo expectations define the basic rights and obligations of the parties involved, and therefore affect vital values. These rights and obligations form the two types of status quo expectations. As Table 2.1 shows, they involve claims, privileges, responsibilities, duties, and so on. Note especially that expectations about property--who owns what--are part of the status quo.

Obviously, the division between status quo and non-status quo expectations is not clear-cut. The criterion of discrimination is salience to fundamental values, and thus intensity of feeling and commitment. For example, agreements over property (such as territory) will usually involve strong emotion and commitment, while agreed upon rules or practices, advantages or benefits are less vital and violations more tolerable. However, we are dealing here with a great complexity of social contracts and the subjectivity of underlying interests, meanings, and values. In some situations a rule, payment, or service may be a life-or-death matter or a question of fundamental principle to the parties involved and thus, for this case, a matter of the status quo. Therefore, the classification of expectations under status quo or non-status quo divisions in Table 2.1 simply attempts to make intelligible the diversity of expectations, rather than to construct conceptually tight demarcations covering all possibilities.

B. Non-Status Quo. One type of non-status quo expectations is distributional, establishing which party can anticipate what from whom, such as benefits, advantages, and services. The two remaining types guide or prescribe behavior between the parties. The social contract often includes rules, customs, or practices that provide standards or define customary or repeated actions. Such may be commands, authoritative standards, or principles of right actions. They may be binding, acting to control or regulate behavior. Such prescriptive expectations in social contracts are mores (long-term, morally binding customs), norms, the law-norms of groups,23 or the customary or positive law of societies or states. Even the "rules of morality constitute a tacit social contract" (Hazlitt, 1964: xii).

C. Overall. Regardless of whether the focus is the rights or obligations, the distributions, or the guides or prescriptions between parties structured by their social contract, these expectations share one characteristic: they circumscribe a region of predictability, or social certainty, between the parties. With a social contract, each party can reliably foresee and plan on the outcome of its behavior regarding the other, as over, for example, claims, privileges, duties, or services. What responses to anticipate, the prospect of reciprocity, the likelihood of particular sanctions, are clear. Social contracts are thus our social organs of peace, extending into the future mutual paths of social certainty and thus confidence.

2.3.2 Theoretical Dimensions

A. Actuality. In Table 2.2 I list 11 theoretical dimensions along which social contracts vary, and have organized them into four general types.24 To begin with, social contracts may be informal, as are unwritten understandings between friends or allies; or they may be formal, as with treaties. They may be implicit, tacit agreements that the parties choose not to mention, as a wife's acceptance of her husband's affairs; or they may be explicit, such as a verbal contract. They may be subconscious, as when co-workers unconsciously avoid sensitive topics over which they might fight. Or, of course, the social contract may be conscious.

These three dimensions--in formal versus formal, implicit versus explicit, and subconscious versus conscious--concern the actuality of social contracts, whether they are a latent agreement underlying social behavior or a manifest compact of some kind.25 A fourth, quite important dimension defines how a social contract is manifested.

A direct social contract is a specific agreement between particular parties. It gives or implies names, dates, places, and definite expectations. Contracts are usually thought of as this kind, such as a construction contract between two firms or a trade treaty among three states. However, direct contracts may overlap or be interconnected through the different parties, and thus form a system of contracts. And these systems themselves may overlap and be interdependent. Out of these diverse, interconnected, and related direct contracts and systems of contracts will develop more general expectations, such as abstract rules, norms, or privileges at the level of the social system itself. No one will have agreed to these expectations per se, nor are they connected to any particular interest, but they nonetheless comprise a social contract (albeit an indirect one) covering the social system. The prices of goods in a free market comprise such an indirect social contract evolving from the diverse direct contracts between buyers and sellers.26 In Section 2.3.3 I will present some of the major forms direct contracts may take; in subsequent sections I will describe several orders of direct and indirect contracts.

B. Generality. A second type of theoretical dimension delineates a social contract's generality. One such dimension concerns whether a contract is unique or common. A unique social contract is a one-time-only agreement within a unique situation and concerning nonrepetitive events or interaction between the parties. Such is the implicit agreement wrought in an alley by a thug, whose knife coerces you to hand over your money; another example is a two-hour ceasefire agreement to enable combatants to clear the battlefield of wounded, or a neutral state granting American relief planes a once-only flyover to rush food and medicine to earthquake victims in a neighboring state. By contrast, a common social contract involves repeated events or patterns of interaction. Treaties, legal contracts, constitutions, and charters are usually of this type. Clearly, the unique-common dimension is a continuum, since between the unique two-minute holdup and the common, overriding political constitution of a state are a variety of social contracts combining in different ways unique and common expectations.

Turning to the second generality dimension shown in Table 2.2, social contracts may be bilateral, involving only two parties, multilateral in covering more than two parties, or collective. The latter covers a society, community, or a group. Constitutions or charters are of this type, as are an organization's bylaws. While this may seem clear enough, there is an intellectual trap to avoid here--that of always viewing collective social contracts as necessarily constructed, designed, or the explicit and conscious outcome of a rational process of negotiation.27 Collective contracts also may emerge from the interwoven, multilayered, bilateral and multilateral social contracts crisscrossing a society. The integrated system of abstract rules, norms, mores, and customs spanning a society form an indirect, collective social contract. It is implicit and informal; its expectations are partly conscious, partly unconscious. The system of informal rules of the road is such a collective agreement governing, along with coextensive formal traffic laws, a community of drivers.

While no group of people may have formally or consciously agreed to a collective social contract--while such may emerge from various, lower-level social contracts, many of which are conscious agreements--it is still based on a particular balance of powers, now involving all members of the collective. Consider, for example, the historically rapid dissolution and restructuring of collective expectations involving rules, customs, and laws that have occurred as a result of conquest (such as Latvia, Lithuania, and Estonia conquered and absorbed by the Soviet Union in 1939), of military defeat and occupation (as of Hitler's national socialist, totalitarian Germany), or revolution (witness the French and Russian Revolutions, or the 1974-1978 Cambodian social revolution of the Khmer Rouge). Of course, not all norms, customs, or customary laws are changed, no more than a new bilateral or multilateral contract will discard all previous expectations. New social contracts build on the old. However, a new social contract, collective or otherwise, will be meaningfully different; associated interaction between the parties will change significantly.

Finally, the third dimension defining a contract's generality may be narrow, middle range, or overarching. A narrow contract concerns only a few interests, events, or behaviors, such as a contract to paint a car, a trade treaty increasing the quota on imported sugar, or the price of a Sony television set.28 An overarching contract develops from, refers to, or spans a whole system of relationships, such as those of a family, the larger society, or an organization. A marriage contract stipulating duties and rights of spouses, an organization's constitution, or the system of norms covering a society are some examples. Between the narrow and overarching are a variety of middlerange social contracts covering or involving a large amount of behavior, but not the whole society. One's work contract, an alliance between states, and a peace treaty are examples in this middle range.

C. Polarity. The third type of dimension shown in Table 2.2 concerns a social contract's polarity. In the dimension of coerciveness, the parties to social contract may voluntarily accept it, or one or more parties may be coerced into it, either by other parties to the contract or by a third party, such as in a shotgun wedding or governmentally imposed, union-management contract. Between freely determined and coerced contracts are those which one or more parties agree to out of necessity. That is, circumstances, the environment, or events leave virtually no realistic or practical choice. In a one-company mining town where a person has his roots, he may have little, socially meaningful choice but to contract for work with the company. To defeat Hitler in the Second World War, Churchill felt he had little choice but to form an alliance with Stalin.

A second polarity-type dimension concerns whether a social contract is solidary, neutral, or antagonistic.29 Solidary expectations derive from helpful, altruistic, or compassionate behavior. Such expectations are common among close friends or relations, lovers, or close-knit communal or religious groups. Antagonistic expectations, however, derive from mutually competitive, divergent, or opposing behavior. They involve a perception of incompatible purposes, temporarily bound in a social contract, and a belief that satisfying one's interests entails frustrating those of the other parties. A labor-management contract achieved after a long, violent strike is such an antagonistic contract; or a truce between traditional enemies, such as Pakistan and India, North and South Korea, or Israel and Syria. Between solidary and antagonistic contracts lie neutral contracts,30 those which are strictly a matter of business, a question of the parties coolly and objectively satisfying rather specific interests. Examples are agreements for a bank loan, renting an apartment, importing cotton, or increasing the postage on international mail.

D. Evaluative. Finally, there is the evaluative dimension. One of these concerns whether a social contract is good or bad. Fundamental philosophical controversy centers on the idea of good. For the moment, I mean "good" simply in the sense that one might say a treaty is a good one because it has characteristics that one desires or believes rationally commendable or divinely inspired.31

A contract may be positive or negative in the same sense as "good" or "bad." There is a potential confusion in the use of these terms, however, since here a social contract equals peace. "Positive peace" has come to mean, especially among Scandinavian irenologists32 an existing or ideal social state, such as the achievement of individual potential, as reflected in social equality, for example. "Negative peace" is then simply the absence of violence. This, however, is a confusion of categories, and leads to such strange but consistent (by definition) expressions as "a positive, negative peace."33 Simply, I will mean positive as good and negative as bad in qualifying social contracts or peace.

A second evaluative dimension defines one kind of good social contract: whether it is just or unjust. It is this dimension of social contracts that is the major focus of this book. Understanding that a social contract defines a particular peace, my question is: What is a just peace? My answer, developed in Part II is that justice is the freedom of people to form their own communities or to leave undesirable ones . For large-scale societies, just peace is promoted through a minimum government.

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2.3.3 Forms

Table 2.3 presents major forms of direct social contracts. There is no need to describe each in detail here. Suffice to say that each is a structure of expectations based on a definite balance of interests, capabilities, and wills. Each is a social island of peace.

2.3.4 Social Orders
A social order is a particular arrangement of direct and indirect social contracts forming a meaningful, causal-functional34 whole. Two types of social orders are of concern here. One is that of groups; the other of societies.
A. Groups. A group is structured by a direct, overarching social contract that defines members' rights, obligations, and authoritative roles. Behavior is guided and prescribed by sanction-based law-norms. All this may be codified in organizing documents, such as a charter, constitution, or bylaws; or these may be informal, implicit, or even subconscious understandings and norms evolving from the spontaneous interaction and conflicts of group members, as in a family or clan.35

In any case, this social contract may be solidary, neutral, or antagonistic (as in family, work group, and prison, respectively); it may tightly organize members or leave them unorganized; and it may recruit members voluntarily, through coercion, or out of necessity. Group goals may be diffused or superordinate; the basis of authoritative roles may be legitimacy or threats. These diverse characteristics shape the five groups shown in Table 2.4.36

For my purposes here, the most important distinction is between spontaneous groups and voluntary associations on the one hand, and voluntary, quasi-coercive, and coercive organizations on the other. An organization is structured by an explicit, formal social contract aimed at achieving some superordinate goal (profit for a business, military victory for an army, segregating criminals for a prison, education for a university). Expectations are wrapped around this goal: it determines roles, rights, and obligations, as well as law-norms prescribing behavior. An organization is then an antifield.37 Spontaneous interaction is circumscribed, consigned to regions of social space (the interstices of the organizational chart) irrelevant to an organization's goals. By contrast, voluntary groups and associations are less organized, not as strongly directed toward some superordinate goal. Goals may even be absent, diffuse, or unarticulated. Coercion or authority play minor roles. Within these groups and associations field forces and processes have considerable freedom and scope, as in a family, friendship group, or neighborhood association.

These different groups define different structures of peace, different patterns of our interests and capabilities, of our powers.

B. Societies. The second kind of social order shown in Table 2.4 is the society. The three pure types listed have been discussed at length in Vol. 2: The Conflict Helix38 and their empirical validity was assessed there.39 Here, I need only note the more important relevancies.

A society is defined by a division of labor40 and, accordingly, certain shared meanings, values, and norms; social interaction; and a communication system. It is shaped by an indirect, overarching, collective structure of expectations--a mainly informal and implicit social contract. The form of social power primarily underlying this contract determines the type of society. An exchange society is dominated by exchange power; an authoritative society by authoritative power; a coercive society by coercion. By virtue of the dominating form of power and associated social dynamics, each society manifests a particular dimension of conflict, with exchange societies least violent; coercive, the most.41 Each type of society is thus a different kind of peaceful order.

International relations among societies are of special importance here. Nation-states form an exchange society42 with a libertarian government, pluralistic conflict,43 and associated pluralistic structure of peace. In later discussing international peace I will make use of this social fact.

C. Summary. I have shown the diversity of social contracts, and thus peace, through detailing their various expectations, dimensions, forms, and orders. I need only underline now the nested, overlapping, and hierarchical complex of such contracts filling out the structure of a group or society. Consider, for example, a voluntary organization such as a university. It has an overarching contract defining its purposes, organizational structure, positions, and attendant rights and obligations, and associated rules and law-norms. Under the cover of these expectations are defined related social contracts and systems of contracts governing separate administrative functions (such as admission and financial aid), colleges, divisions, and departments. Within the constraints of the university's overarching expectations, each contract or system has a certain life, depending on the administrators, deans, and faculty involved. Each teaching department within a college of division achieves its own informal or formal social contracts establishing rights, obligations, and privileges attendant upon faculty and student rank and defining the role of students and rules for judging issues before the department. As should be clear, each department, college, and administrative division will be an arena of conflict establishing or revising such expectations, although the overarching social contract that constitutes the university remains stable--a region of social peace at its level.

The university itself is within an overarching social contract that is the larger society. Families, Businesses, universities, governments, churches, are all are collective social contracts within society, which also includes the numberless bilateral and multilateral social contracts among groups, subgroups, and individuals and the collective contracts ordering subsocieties. Each social contract is a specific peace within a particular conflict helix; each may have within it lower-level conflict (for example, a state within a region of international peace may suffer internal guerrilla war and terrorism); each peace may exist within an ongoing, antagonistic conflict (as internally peaceful states engage in war).

Peace is therefore complex, multilayered. To say the least, discussing peace requires being specific about the social contract involved. To present a theory about a just peace demands clarity about the associated expectations, dimensions, and social orders.

2.4 CONCEPTUAL LEVELS AND DIMENSIONS OF PEACE
The dimensions, forms, and orders of social contracts described above are also, by definition, those of peace. What must be added here and in the next Section are additional distinctions not usually applied to social contracts but which help locate peace as a social contract among our diverse conceptualizations of peace. This and Section 2.5 also represent part of my effort at vocabulary building--developing in a systematic manner, and locating in one place, those terms applicable to peace that will be used in subsequent chapters.

Table 2.5 presents the conceptual level and dimensions of peace to be discussed here.

2.4.1 Conceptual Levels
A. Levels. Undoubtedly, peace is often conceptually opposed to war. Obviously, then, one conceptual level for analyzing a just peace involves those social contracts determined by international, civil, or revolutionary war.
Peace, however, especially among pacifists, is also opposed to violence. This includes war, of course, but additionally covers violent acts not ordinarily thought of or legally defined as war. Indeed, in the contemporary world legal war (that is, war as a legal state of relations invoking special international laws) is rare, while warlike violence is as intense and prevalent as wars were during past centuries. Nonetheless, this is more than a matter of defining war empirically. Many do feel that peace, conceptually, applies only to those human relations which exclude personal, organized, or collective violence.

Those opposing the idea of peace to violence or war usually see peace as an absence of such behavior. But a different view, especially in the East, sees peace as harmony, tranquility, concord. Peace is then conceptually opposed to nonviolent, antagonistic conflict, such as that manifesting threats and accusations, hostile quarrels, angry boycotts, and riotous demonstrations.

Another concept goes even further, seeing peace as absolute harmony, serenity, or quietude; that is, as opposed to any kind of conflict, antagonistic or otherwise. Conflict is a general concept meaning, in essence, a balancing of power,44 which may involve not only hostile or antagonistic balancing but also that of intellectual conflict (as in friendly disagreement over facts), bargaining conflict (as in haggling over a sale price), or a lover's conflict (as when each tries to give the other the choice of a movie to see). Each of these conflicts ends in a social contract, and therefore in a kind of peace. I mention this conceptual level for completeness, however. My conceptual focus here, as for all irenologists, will be on peace at the level of antagonistic conflict, whether violent or not.

B. A Threshold. Especially significant for a theory of just peace is the distinction between nonviolent, antagonistic conflict on one side and violence on the other. There is an empirical threshold here. As I will argue later in Section 7.4.2 and Section 8.2, the conditions for a just peace at the level of violence will increase the amount of nonviolent conflict. A just peace free from long-term violence is, at the level of societies at least, only possible at the price of peace from nonviolent conflict.

2.4.2 Social Levels
A. Levels. Clearly, peace as a social contract occurs at different levels of social relationships. Table 2.5 lists four of concern here. One is international, the level of most historical concern about peace. A second level concerns the central government or ruling power (such as a dominant religious leader or political party) of a state. Peace here is the outcome of, or can disintegrate into, revolution or civil war; guerrilla war and terrorism; political turmoil involving riots, demonstrations, general strikes, and assassinations.
A third level involves group relations within states, such as among religious and ethnic groups, nationalities, classes, castes, unions, and families. A state, at the level of its central government, may be peaceful, manifesting a stable social contract, while some of its regions may experience continuing group violence. The final level involves the interpersonal relationships among individuals.

B. Crosscutting Levels. Social levels of peace are crosscutting: each of the conceptual levels may refer to any one of the social ones. Even war is applicable to individual relations, as when conflict goes beyond a violent incident to involve a campaign of violence to defeat or destroy another person.

It should, be clear, then, that there may be peace from war, but not from antagonistic, nonviolent conflict. Moreover, there may be peace from international war, while internal war rends a state. Conversely, a state may be at peace while engaged in international war. Peace among states may be widespread, central state governments may be stable and secure, while some groups in one province, region, or other political subdivision are locked in total war. From the perspective of a particular citizen, his state and social groups all may be at peace, while personal peace eludes him--he simply may not get along with his neighbors or co-workers.

Peace is thus multilayered and complex. This must be kept in mind in defining a just peace.

2.4.3 Conceptual Dimensions
A. The Metalevel. Section 2.3.2 presented major theoretical dimensions of social contracts, and thus of peace. The dimensions considered here and shown in Table 2.5 refer only to peace as a concept and not the concept of peace. This is like the difference between ethical and metaethical concepts, or political and metapolitical ones. In each case, the former refers to the content; the latter to the concept about the contents.45 For example, a peace can be overarching (Table 2.2); a concept of peace can be abstract.
B. Empirical Concept. The first such dimension defines whether the concept is empirical, abstract, or theoretical--a construct.46 An empirical concept47 of peace refers to readily observable phenomena. It is measurable (operational). Peace as absence-of-killing violence is such a concept; as is peace as an absence of legally declared war or a peace treaty (or any written social contract, for that matter).

C. Abstract Concept. While also referring to empirical phenomena, an abstract concept of peace is not directly observable. Rather, it usually denotes a bundle of empirical attributes or qualities, or is reflected in patterns of behavior. Examples are concepts such as status, power, or ideology, which are detached from particular instances or events or specific empirical characteristics. Abstract concepts provide general, theoretical understanding of social reality, while empirical concepts are usually common-sense descriptions of immediate perception.48 For general use peace as a social contract would be an abstract concept, although some social contracts may be quite concrete and hence empirical. The abstraction involved is clearest when we consider implicit, or even subconscious, agreements involving tacit expectations. The abstract, nonformal rules of the road are part of such an abstract social contract. And consider the overarching social contract whose expectations define rules and norms spanning society but which no one signed or directly agreed upon, which few are aware of, but which most obey. Most families are integrated by such expectations that wife and husband, parents and children have of each other but which an observer would have difficulty defining empirically (although certainly indicators could be developed, as for status or power).

Peace as a social contract is an abstraction within the idea of a conflict helix, which is part of social field theory. This theory provides an explanation of conflict, violence, war, and peace. So much, I trust, was made clear in Vol. 2: The Conflict Helix and Vol. 4: War, Power, Peace.

There are other abstract definitions of peace: For example, peace as law or justice; or peace as concord, harmony, or tranquility. Often the theoretical context for an abstract definition of peace is not explicit, but nonetheless is clear from the context within which the concept is developed or used.

D. Construct. Finally, peace as a construct49 means that "peace" serves a stepping-stone role in theory. It is a theoretical concept; analytic, not synthetic. The content given to a construct is not defined independent of a theory but wholly within the operations and deductions of a theory. By contrast, while measurements or indicators of an abstract concept certainly would be directed by a theory, the actual data (or content) are collected (or observed) independently.

This is a difficult but important idea, and I would like to take a moment to make it clear. Consider a simple explanatory theory that y = h + tx, where y is the level of armaments of state i, x is the level of armaments of an opposing state j, and t and h are theoretical coefficients conceptualized as "x's perception of threat from y," and "the hostility that j feels toward i," respectively.50 This simple explanatory theory says that one state's armaments are a function of those of the opposing state's, depending on its perception of the threat from the other and its hostility toward it. Now y and x are abstract concepts, since "armaments" is a concept covering a tremendous empirical diversity of weapons and indicators. Nonetheless, by adding auxiliary statements to the theory one might measure armaments through such indicators as defense expenditures or number of armed military personnel. Data on these indicators could then be collected from sources readily available and independent of the theory.

However, within this theory, threat and hostility are constructs. No measurement of them or indicators need by given; no data collected specifically on them. Rather, the coefficients are totally defined by fitting y = h + tx to the data on x and y. Such a fit could be made by bivariate regression analysis where h is the intercept and t the regression coefficient; y the dependent and x the independent variables. This gives numerical values to h and t without any specific data collected on them. As constructs, they would have been given empirical content totally dependent on the theory y = h + tx and data on x and y.

Keeping this simple arms theory in mind, I must now discriminate between the loose and tight versions of social field theory. In the loose version (specifically, that presented in most of these volumes, especially concerning the conflict helix), the mathematical structure of field theory is usually background;51 content, conceptual understanding, and explanation are usually foreground. A structure of expectations--social contract--is treated as an abstraction. It is given ostensive content, such as in discussing a union-management contract, an implicit agreement ending a family quarrel, an international settlement of a dispute, or the law-norms integrating a group.

In the tight theory,52 mathematical structure, substantive interpretation of primitive terms or constructs,53 operationalization, and empirical tests are of concern. The tight theory is meant to be as explicit, formal, and general as possible. Expectations are constructs weighting behavioral dispositions in a social field and technically function as canonical coefficients in application.54 And to enhance the theory's generality, I have considered a structure of expectations as implicitly an indirect, overarching social contract of a social field (such as a spontaneous or self-organizing55 society). This structure is a cooperative component--another construct56--underlying the variation in manifest interaction. It is reflected in common patterns of social interaction, and thus is empirically measured indirectly only by a mathematically defined axis lying through an empirical pattern of social interaction spanning society.57

For the tight theory, then, applicable to an indirect, overarching social contract for social fields, peace is a construct. Its whole meaning is given by the theory; it serves to aid empirical explanation and theoretical understanding; its empirical content is traced by the cooperative patterns of social interaction.

In this Vol. 5: The Just Peace I will not deal with the tight theory, whose role is precise and testable scientific explanation, not intuitive understanding. The loose theory will provide sufficient framework for our purposes here. And, as in previous volumes, I will treat peace as an abstraction, even when referring to indirect, overarching social contracts.

Incidentally, peace as a construct is not unique to field theory, although as far as I know no other such tight theory so treats it. Peace as divine grace in Christian theology or as shalom in Judaism, of which one meaning is a covenant with Jehovah, are constructs. Their empirical meaning is not given directly or abstractly; rather, they are primitive terms whose content comes from the empirical nature of other, linked theological concepts. Moreover, the concept of "positive peace" developed by Johan Galtung is a construct within a neo-Marxist theory of exploitation; "positive peace" has no direct empirical or indirect abstract empirical content, but is defined as the ability of individuals to realize their potential, which in turn is equated in theory with equality, itself an abstraction measured by various indicators of equality.58

E. Descriptive-Normative. The empirical-abstract-construct dimension of peace concepts is the first conceptual dimension. The second defines whether the concept of peace is descriptive or normative. A descriptive concept is one simply denoting some aspect of reality, such as trade, state, or president.

A normative concept is evaluative, denoting or implying goodness, desirability, what ought to be, or the negation of these denotations. Compassion, equality, and exploitation are such normative concepts. Clearly, the same concept may be used descriptively or normatively depending on context and intent. However, some concepts have a built-in evaluation that even a careful descriptive analysis may not avoid, such as with the concepts murder, torture, exploitation, charity, and love. As with love, peace undefined is an implicit good, a hope, desire, a human ideal. "Give peace in our time, 0 Lord."59 In its common usage, peace is normative.

However, regardless of the affective connotation of peace, the concept can be used descriptively. For example, if peace is conceived as an absence of war or a peace treaty, it is possible to write about the peace in Europe since 1945, the peace of the Versailles Treaty, or the average periods of peace in history, without necessarily connoting that these are good historical periods (although for pacifists, peace as an absence of war is, ipso facto, good in all contexts).

My use of peace as a social contract is meant descriptively. Not all social contracts are good. Some are quite bad,60 as was the horrible peace (as absence of international war) of the Khmer Rouge over Cambodia in 1974-1978 (before the Vietnamese invasion). Since peace is meant here to be (normatively) as neutral a concept as possible, it is sensible to ask when peace is good, or (as a subcategory of the good) when it is just--or when bad or unjust. For the very reason I have treated peace descriptively in previous volumes, even though it is my fundamental normative goal, I now must conclude by pointing out in this Vol. 5: The Just Peace when peace, so described, is just or unjust and, given my analyses and results, what will foster a just peace.

2.5 QUALITIES OF PEACE

2.5.1 An Existent

Table 2.6 presents four qualities of peace entailed by my conceptualization. Clearly, from Section 2.2, peace is a sociopsychological existent. It has dispositional and manifest61 being. In this it is on a par with conflict.62 Conflict is manifested in particular patterns of behavior; so is peace.63 Conflict and peace may be absent, as when two individuals or groups lack contact or awareness of each other. And conflict and peace are coupled existents, closely related within a social process I call the conflict helix.
Other conceptualizations also treat peace as an existing something, such as peace as harmony, integration, or virtue. However, the currently conventional definition of peace as the absence of violence or war treats peace as a void, a nonexistent. This creates several analytical problems, which will be mentioned below.64

2.5.2 Dichotomous
Peace as an existent is dichotomous: it is or it is not. It would be meaningless to talk about more or less of a peace, as it would be meaningless to talk about more or less of a contract, a nation-state, a president, or an elephant.65 Of course, a state may be large or small, rich or poor. Likewise, peace varies along several dimensions; it may take on different forms or social orders.66
It is necessary here, then, to remember the distinction between a peace existing or not and the attributes, form, or order of the peace that exists. Thus, I might say that peace in the world is increasing and mean that more states are subscribing to a particular overarching, international peace. Or by saying that peace is more intense I might imply that a specific peace is involving more and more cooperative interaction.

2.5.3 Internal and External
In my view, peace is internal and external. It is a social contract among people or groups involving these psychological and social realities. The former comprises the parties' expectations and the congruence of these expectations with their mutual interests, capabilities, and wills. These are all psychological variables. The social reality, manifesting the harmonization of certain expectations among the parties, may be evidenced in specific documents (such as a written contract), physical structures (such as certain government buildings), and patterns of cooperative interaction. To say, then, that peace is an existent means that the particular expectations, meanings, and values within the minds of the parties and their social manifestations are all causally-functionally67 integrated into a social contract. Thus, like an iceberg, peace seen on the surface of social relations is only a small part of the overall structure.68

2.5.4 Active
Finally, peace as a social contract is active, not passive. It is created through negotiation, adjustment, resolution, decisions. It comprises predictions (expectations) about the future. It is manifested through cooperative interaction. Its existence depends on congruence with the balance of powers. It is a phase in the dynamics of the conflict helix.
By contrast, peace as the absence of violence or war is passive. True, it may be generated by negotiation and resolution. But the resulting peace is inactive, inert. It is a social void-something to build a wall around to protect and maintain. Any condition or structure or lack thereof constitutes such a peace as long as there is no social violence-even a desert without human life.69

2.6 ADVANTAGES OF
THIS CONCEPTUALIZATION
Peace conceptualized as a social contract has a number of advantages. First, peace is then defined as part of a dynamic social process with a well-defined nature; it is given meaning and substance in definite relationship to conflict and cooperation.
Second, peace stands in clear theoretical and substantive relationship to such important concepts as perception, situation, expectations, interests, capabilities, will, power, status, class, and behavior.70 This gives the nature of peace considerable substantive and theoretical clarity. That is, peace is locked into an overarching social theory.

Third, as a social contract peace is operational, and empirical patterns of peace, so defined, have been well delineated.71

Fourth, because of the theoretical and substantive meaning of peace, peacemaking and peacekeeping policies are given concrete direction and crucial variables are spotlighted. For example, keeping the peace then depends, most generally, on maintaining congruence between the balance of powers and the structure of expectations (social contract). This might be done by altering expectations unilaterally to adjust to changing capabilities, or strengthening will to lessen a developing gap with expectations.72

Fifth, peace as conceptualized embodies a number of psychological principles, such as subjectivity, intentionality, free will, and individualism.73 This, plus the social principles mentioned in the previous Section, enable a clear and straightforward application of the social contract theory of justice. As will be shown in the next part, a just peace is a hypothetical social contract of a particular kind, one to which individuals would fairly and impartially agree.

* * *
This Chapter has described peace as a social contract. And it has made the necessary definitions and distinctions in order to compare this idea of peace to alternative conceptualizations.

The Adisham bungalow

2009-10-24T08:31:00.000-07:00

The adisham bungalow was built by sir Thomas Adisham bungalow is located with a distance of 4km from Haputale, a misty town in the southern edge of the Central range of mountain in SriLanka. it was built by Sir Thomas Lister Villiers, who was a grandson of Lord John Russell, twice prime minister of Britain.

While Sir Thomas was being the chairman of George Steuart Company, he built the Adisham as his dream house in an idyllic site at Haputale, surrounded by virgin forest and commanding views across hills and valleys.

The house was designed in the Tudor style, on the lines of Leeds Castle in Kent, with stout granite walls of locally quarried stone, long, narrow turret windows and chimneys.The roof was covered with flat Burma teak shingles. The doors, windows, paneling, staircase and floors were all of Burma teak. The lay-out of the garden was also British.

Today's Adisham is primarily a monastery, where a few monks follow a schedule of prayer, meditation, work and service. Adisham has made itself famous for fine products such as strawberry jam, orange marmalade, wild guava jelly and fresh fruit cordials.

The planets

2009-10-24T07:12:00.000-07:00

The Planets (plus the Dwarf Planet Pluto)
Our solar system consists of the sun, eight planets, moons, dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The sun is the center of our solar system; the planets, their moons, the asteroids, comets, and other rocks and gas all orbit the sun.

The nine planets that orbit the sun are (in order from the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet or plutoid). A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane, the ecliptic (Pluto is an exception; it has an elliptical orbit tilted over 17° from the ecliptic).

Easy ways to remember the order of the planets (and Pluto) are the mnemonics: "My Very Excellent Mother Just Sent Us Nine Pizzas" and "My Very Easy Method Just Simplifies Us Naming Planets" The first letter of each of these words represents a planet - in the correct order.

The largest planet is Jupiter. It is followed by Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury, and finally, tiny Pluto (a dwarf planet). Jupiter is so big that all the other planets could fit inside it.

The Inner Planets vs. the Outer Planets
The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun).
The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons.
The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet). They are mostly huge, mostly gaseous, ringed, and have many moons (again, the exception is Pluto, the dwarf planet, which is small, rocky, and has one large moon plus two tiny ones).

Temperatures on the Planets
Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere.

Density of the Planets
The outer, gaseous planets are much less dense than the inner, rocky planets.

The Earth is the densest planet. Saturn is the least dense planet; it would float on water.

The Mass of the Planets
Jupiter is by far the most massive planet; Saturn trails it. Uranus, Neptune, Earth, Venus, Mars, and Pluto are orders of magnitude less massive.

Gravitational Forces on the Planets
The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared.

A Day on Each of the Planets
A day is the length of time that it takes a planet to rotate on its axis (360°). A day on Earth takes almost 24 hours.

The planet with the longest day is Venus; a day on Venus takes 243 Earth days. (A day on Venus is longer than its year; a year on Venus takes only 224.7 Earth days).

The planet with the shortest day is Jupiter; a day on Jupiter only takes 9.8 Earth hours! When you observe Jupiter from Earth, you can see some of its features change.

The Average Orbital Speed of the Planets
As the planets orbit the Sun, they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion).

The Planets in Our Solar System
Planet Distance from the Sun
(Astronomical Units
miles
km) Period of Revolution Around the Sun
(1 planetary year) Period of Rotation
(1 planetary day) Mass
(kg) Diameter
(miles
km) Apparent size
from Earth Temperature
(K
Range or Average) Number of Moons
Mercury 0.39 AU, 36 million miles
57.9 million km 87.96 Earth days 58.7 Earth days 3.3 x 1023 3,031 miles
4,878 km 5-13 arc seconds 100-700 K
mean=452 K 0
Venus 0.723 AU
67.2 million miles
108.2 million km 224.68 Earth days 243 Earth days 4.87 x 1024 7,521 miles
12,104 km 10-64 arc seconds 726 K 0
Earth 1 AU
93 million miles
149.6 million km 365.26 days 24 hours 5.98 x 1024 7,926 miles
12,756 km Not Applicable 260-310 K 1
Mars 1.524 AU
141.6 million miles
227.9 million km 686.98 Earth days 24.6 Earth hours
=1.026 Earth days 6.42 x 1023 4,222 miles
6,787 km 4-25 arc seconds 150-310 K 2
Jupiter 5.203 AU
483.6 million miles
778.3 million km 11.862 Earth years 9.84 Earth hours 1.90 x 1027 88,729 miles
142,796 km 31-48 arc seconds 120 K
(cloud tops) 18 named (plus many smaller ones)
Saturn 9.539 AU
886.7 million miles
1,427.0 million km 29.456 Earth years 10.2 Earth hours 5.69 x 1026 74,600 miles
120,660 km 15-21 arc seconds
excluding rings 88 K 18+
Uranus 19.18 AU
1,784.0 million miles
2,871.0 million km 84.07 Earth years 17.9 Earth hours 8.68 x 1025 32,600 miles
51,118 km 3-4 arc seconds 59 K 15
Neptune 30.06 AU
2,794.4 million miles
4,497.1 million km 164.81 Earth years 19.1 Earth hours 1.02 x 1026 30,200 miles
48,600 km 2.5 arc seconds 48 K 2
Pluto (a dwarf planet) 39.53 AU
3,674.5 million miles
5,913 million km 247.7 years 6.39 Earth days 1.29 x 1022 1,413 miles
2,274 km 0.04 arc seconds 37 K 1 large (plus 2 tiny)
Planet Distance from the Sun
(Astronomical Units
miles
km) Period of Revolution Around the Sun
(1 planetary year) Period of Rotation
(1 planetary day) Mass
(kg) Diameter
(miles
km) Apparent size
from Earth Temperature
(K
Range or Average) Number of Moons

Another Planet?
In 2005, a large object beyond Pluto was observed in the Kuiper belt.

A few astronomers think that there might be another planet or companion star orbiting the Sun far beyond the orbit of Pluto. This distant planet/companion star may or may not exist. The hypothesized origin of this hypothetical object is that a celestial object, perhaps a hard-to-detect cool, brown dwarf star (called Nemesis), was captured by the Sun's gravitational field. This planet is hypothesized to exist because of the unexplained clumping of some long-period comet's orbits. The orbits of these far-reaching comets seem to be affected by the gravitational pull of a distant, Sun-orbiting object.

Planet Activities and Quizzes
Planet Coloring pages

An interactive puzzle on the Solar System.

Find It!, a quiz on the planets.

A fill-in-the-blank (cloze) activity on the Solar System - or go to the answers.

Solar System Model to make.

Solar System calendar to print out and color.

Solar System Crafts

How to write a report on a planet - plus a rubric.

Astronomy: K-3 Theme Page
Activities, quizzes, books to print, and printouts.

Nine Planets
A Book With Tabs
An activity book on the Solar System to print for fluent readers. The book contains information, pictures, and questions to answer.

The Solar System Book
A simple printable coloring book about the Solar System to print (for early readers). Pages on the Solar System, the sun, Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Solar System Coloring Book

Color and learn about our Solar System, the Sun, the planets, asteroids, comets, and our moon.

Solar System Diagram
Label the Sun and planets.
Answers

Earth's Atmosphere
Label the atmospheric layers of the Earth.
Answers

Earth Diagram
Label the inside of the Earth.
Answers

Celsius Bar Graph Questions #2:
Printable Worksheet
A printable activity worksheet in which the student reads a bar graph of the average temperatures of the planets to answer questions, for example, "On average, is it warmer on Jupiter or Mars?" Or go to the answers. Go to a pdf version of the worksheet.

Moon Phases Diagram
Label the phases of the waxing and waning moon.
Answers

Lunar Eclipse Diagram
Label the lunar eclipse.
Answers

Planet-Sun Orbital Diagram
Label the aphelion (farthest point in orbit) and perihelion (closest point in orbit) of a planet in orbit.
Answers

Put 10 Planet Words in Alphabetical Order - Worksheet
Put 10 planet words in alphabetical order. The words are: Earth, Jupiter, Mars, Mercury, moon, Neptune, Pluto, Saturn, Uranus, Venus. Go to the answers.

The Planets in English
A Label Me! Printout
Label the Solar System in English.
Answers

The Planets in French
A Label Me! Printout
Label the Solar System in French.
Answers

The Planets in German
A Label Me! Printout
Label the Solar System in German.
Answers

The Planets in Italian
A Label Me! Printout
Label the Solar System in Italian.
Answers

The Planets in Portuguese
Label the planets in Portuguese.
Answers

Yala national park

2009-10-24T06:59:00.000-07:00

Yala National Park is geographically located in Sri Lanka at latitude 06°16' - 06°42' North and longitude 81°15' - 81°42' East. The Park can be visited via the town of Tissamaharama in the Hambantota District of the Southern Province.

While Block I has good access roads, access to Blocks II and III is limited mainly to dry weather. There are eight Park bungalows all of which are within Yala Block I. Another has been constructed at Katagamuwa Sanctuary, and one more is now ready for occupation in Yala Block IV. Accommodation is available for 8-10 people in each bungalow on the basis of prior reservations with the Department of Wildlife Conservation. Apart from resident visitors occupying the bungalows, a large number of day visitors enter the Park.

The Block I boundaries of the Park, take in 19 kilometers of sea coast in the southeast from Amaduwa to Yala, 19 kilometers from Yala up the Menik Ganga to Pahalahentota, 19 kilometers from Pahalahentota to Bambawa, and 3 kilometers from Bambawa to Palatupana.

Early History
"The earliest epigraphic "Brahmi" inscriptions discovered in Sri Lanka and in this region date back to the 2nd century B.C. Prior to this the Indo-Aryan settlers from Northern India as represented,in the legend of Vijaya, were well established and in full control of the area. Edifices of the earliest Buddhist cave monastery type began to be constructed wherever there was human habitation and in suitable rock outcrops, of which there are many in the area. There are to this day innumerable and very interesting remains of cave dwellings from the pre-Christian era."

This region was part of the Rohana (Ruhuna) Kingdom, having an advanced civilization as evinced by remains of dagabas and ancient artificial reservoirs (tanks), built by clever hydrological engineers, to irrigate large extents of cultivable land.

After the 10th century, historical evidence draws attention to the absence of inscriptions later than the 10th century A.D. "Architectural and sculptural remains of the medieval period are absent. It would appear to be a justifiable inference that some sudden de-population of the region occurred. The ancient chronicles supply no information whatsoever and the jungle tide spread covering the past with a mantle of secondary forest. These have matured to the climax stands seen in Yala today.

The Modern Era
At the turn of the century Yala Block I was declared a Game Sanctuary. A small area west of the Sanctuary was set aside in which resident sportsman might shoot. The main force behind this decision was the Game Protection Society (now the Wildlife and Nature Protection Society) founded in 1894 by the plantation owners, executives of firms, sportsmen and amateur naturalists favouring the conservation of wildlife. Records denote that the first Game Ranger of the Sanctuary was H.H. Engelbrecht, an Afrikaaner and a Boer prisoner of war who was not returned to South Africa on account of his refusal to swear allegiance to the British monarchy. After his release Engelbrecht came to the nearby coastal town of Hambantota. Being on his own on foreign soil, he found life hard. The Government Agent of the district however, took pity on Engelbrecht and made him the custodian of the Game Sanctuary around 1908. With his experience of wildlife on the veldt, the post suited him admirably. He administered the region fearlessly and with courage, using his whip to punish any miscreants. Many are the tales of his daring and prowess with the gun. However, his German ancestry proved to be his undoing. He was falsely accused during the First World War (1914-1918), of supplying meat to a German warship, the "Emden", and was taken into custody. After the war, he was released and once again returned to Hambantota where he died in poverty. Long after his death, it was proved that he was innocent of the accusation.

Climate
Being located in one of the arid regions of Sri Lanka, the climate of Ruhuna National Park is usually hot and dry. The area receives its annual rainfall during the north east monsoon from November to January, and unpredictable inter-monsoonal rains in March/April and September. February is a dry month, with the dry season proper commencing in June and lasting until September and sometimes until mid October.

The mean annual temperature near sea level is 270C, although in the dry season a daily maximum of 370C is not uncommon.

Physical features
"Most of the area is underlain by Vijayan rocks formed over 600 million years ago. Rock outcrops or inselbergs stand out of a relatively flat plain, looming to heights of up to 800ft. They are made up of migmatites, hornblende, and granite gneisses. Pleistocene and Holocene alluvial and aeolian deposits cover the Vijayan series near the Menik ganga and along most of the coast line."

The Menik Ganga is now a seasonal river, since its damming for irrigation purposes higher up, as far back as 1878. There are four other seasonal "aras" or streamlets carrying water during the rainy season.

The breached and denuded earth bunds of several irrigation tanks are still visible, together with natural water holes and tanks (wewa), improved to hold water. These sources of water are a link in the survival of the wildlife found within the area.

Amongst the rock ridges and monoliths are several natural rock pools that have a charm of their own. Some contain water throughout the year, and have their own development of water plants and fauna.

In the southeast, the Park is bounded by the sea. The many bays carve out an intricate mosaic. Unspoilt natural beaches and sand dunes provide a beautiful environment of undulating and shifting sands. This is surely one of the most spectacular seascapes of Sri Lanka. Far out at sea are two lighthouses, Great and Little Basses, which stand on two submerged ridges by those names and beam a red and white light respectively at night.

Lagoons fringe this part of the coastline, each lined with mangroves and filled with brackish water. The extensive parklands that surround these lagoons offer visitors superb locations for viewing animals and bird life.

The Depth sea

2009-10-24T06:53:00.000-07:00

The sea is one of the great unexplored parts of this planet. In its depths lie great mysteries that will shake the face of our science and civilisation. Some of these have been discovered recently, lifeforms that inhabit hot volcanic vents, creatures with their own light sources, strange structures unlike any seen on the surface. This is a real laboratory of life, as different from the surface as anything that we could imagine on a distant planet. If we can find such novelty here, right under our nose, then just think on the possibilities for life in forms quite alien to those based upon our own DNA.
This possibility is investigated in the field of Artificial Life, here we study processes that resemble those common to the life we know, yet implemented in very alien ways. Our creatures live in silicon, their bodies are made up of patterns of light inhabiting a computer core, they evolve in ways similar to natural life, mutating, having sexual relations, competing for space and time. In this world of tomorrow we see, speeded up a thousand fold, natural selection in action coupled with a new phenomenon, that of self-organization. These systems evolve themselves to an edge of chaos state, the operating parameter that allows them to adapt most efficiently to changes in their environment. This is exactly the same state that we see in natural and human systems, leading many to claim that we have now succeeded in playing God, we have created life itself...

Sinharaja rain forest

2009-10-24T06:51:00.000-07:00

Sinharaja Forest Reserve is a national park and a biodiversity hotspot in Sri Lanka. It is of international significance and has been designated a Biosphere Reserve and World Heritage Site by UNESCO.

The hilly virgin rainforest, part of the Sri Lanka lowland rain forests ecoregion, was saved from the worst of commercial logging by its inaccessibility, and was designated a World Biosphere Reserve in 1978 and a World Heritage Site in 1988. The reserve's name translates as Kingdom of the Lion.

The reserve is only 21 km from east to west, and a maximum of 7 km from north to south, but it is a treasure trove of endemic species, including trees, insects, amphibians, reptiles, birds and mammals.

Because of the dense vegetation, wildlife is not as easily seen as at dry-zone national parks such as Yala. There are about 3 elephants and the 15 or so leopards are rarely seen. The commonest larger mammal is the endemic Purple-faced Langur.

An interesting phenomenon is that birds tend to move in mixed feeding flocks, invariably led by the fearless Greater Racket-tailed Drongo and the noisy Orange-billed Babbler. Of Sri Lanka's 26 endemic birds, the 20 rainforest species all occur here, including the elusive Red-faced Malkoha, Green-billed Coucal and Sri Lanka Blue Magpie.

Reptiles include the endemic Green pit viper and Hump-nosed vipers, and there are a large variety of amphibians, especially tree frogs. Invertebrates include the endemic Common Birdwing butterfly and the inevitable leeches.

Kilimanjaro national park

2009-10-24T06:44:00.000-07:00

Kilimanjaro National Park is a national park, located near Moshi, Tanzania. It is centered on Mount Kilimanjaro, and covers an area of 753 km² (291 square miles) from 2°45'–3°25'S, 37°00'–37°43'E.

In the 1910s, Mount Kilimanjaro and its forests were declared a game reserve by the German colonial government. In 1921 it was made a forest reserve.

In 1973, the mountain above the tree line (about 2,700 m / 9,000 ft) was reclassified as a National Park and was opened to public access in 1977. The park was declared a World Heritage Site by UNESCO in 1987.

Hurricane

2009-10-24T06:35:00.000-07:00

Hurricane Katrina of the 2005 Atlantic hurricane season was the costliest hurricane,[3][4] as well as one of the five deadliest, in the history of the United States.[5] Among recorded Atlantic hurricanes, it was the sixth strongest overall.

Hurricane Katrina formed over the Bahamas on August 23, 2005 and crossed southern Florida as a moderate Category 1 hurricane, causing some deaths and flooding there before strengthening rapidly in the Gulf of Mexico. The storm weakened before making its second landfall as a Category 3 storm on the morning of Monday, August 29 in southeast Louisiana. It caused severe destruction along the Gulf coast from central Florida to Texas, much of it due to the storm surge. The most severe loss of life and property damage occurred in New Orleans, Louisiana, which flooded as the levee system catastrophically failed, in many cases hours after the storm had moved inland.[6] Eventually 80% of the city became flooded and also large tracts of neighboring parishes, and the floodwaters lingered for weeks.[6]

At least 1,836 people lost their lives in the actual hurricane and in the subsequent floods, making it the deadliest U.S. hurricane since the 1928 Okeechobee hurricane. Economist and crisis consultant Randall Bell wrote: "Hurricane Katrina in 2005 was the largest natural disaster in the history of the United States. Preliminary damage estimates were well in excess of $100 billion, eclipsing many times the damage wrought by Hurricane Andrew in 1992."[7]

The levee failures prompted investigations of their design and construction which belongs to the USACE as mandated in the Flood Control Act of 1965 and into their maintenance by the local Levee Boards (who prevented the Army Corps from building flood gates at the mouth of the drainage canals at Lake Pontchartrain).[8] There was also an investigation of the responses from federal, state and local governments, resulting in the resignation of FEMA director Michael D. Brown, and of NOPD Superintendent Eddie Compass. Conversely, the USCG, NHC and NWS were widely commended for their actions, accurate forecasts and abundant lead time.[9]

Four years later, thousands of displaced residents in Mississippi and Louisiana were still living in trailers. Reconstruction of each section of the southern portion of Louisiana has been addressed in the Army Corps LACPR Final Technical Report which identifies areas to not be rebuilt and areas buildings need to be elevated.[10]

Contents [hide]
1 Meteorological history
2 Preparations
2.1 Federal government
2.1.1 Investigation of State of Emergency declaration
2.2 Gulf Coast
2.3 Greater New Orleans area
2.4 Florida
3 Impact
3.1 South Florida and Cuba
3.2 Louisiana
3.2.1 New Orleans
3.3 Mississippi
3.4 Southeast United States
3.5 Other U.S. States and Canada
4 Aftermath
4.1 Economic effects
4.2 Environmental effects
4.3 Looting and violence
4.4 Government response
4.5 Criticism of government response
4.6 International response
4.7 Non-governmental organization response
4.8 Analysis of New Orleans levee failures
4.9 Media involvement
4.10 Retirement
5 Reconstruction
6 See also
7 Bibliography
8 References
9 External links

Meteorological history
Main article: Meteorological history of Hurricane Katrina

Storm pathHurricane Katrina formed as Tropical Depression Twelve over the southeastern Bahamas on August 23, 2005 as the result of an interaction of a tropical wave and the remains of Tropical Depression Ten. The system was upgraded to tropical storm status on the morning of August 24 and at this point, the storm was given the name Katrina. The tropical storm continued to move towards Florida, and became a hurricane only two hours before it made landfall between Hallandale Beach and Aventura, Florida on the morning of August 25. The storm weakened over land, but it regained hurricane status about one hour after entering the Gulf of Mexico.[5]

The storm rapidly intensified after entering the Gulf, growing from a Category 3 hurricane to a Category 5 hurricane in just nine hours. This rapid growth was due to the storm's movement over the "unusually warm" waters of the Loop Current, which increased wind speeds.[11] On Saturday, August 27, the storm reached Category 3 intensity on the Saffir-Simpson Hurricane Scale, becoming the third major hurricane of the season. An eyewall replacement cycle disrupted the intensification, but caused the storm to nearly double in size. Katrina again rapidly intensified, attaining Category 5 status on the morning of August 28 and reached its peak strength at 1:00 p.m. CDT that day, with maximum sustained winds of 175 mph (280 km/h) and a minimum central pressure of 902 mbar. The pressure measurement made Katrina the fourth most intense Atlantic hurricane on record at the time, only to be surpassed by Hurricanes Rita and Wilma later in the season; it was also the strongest hurricane ever recorded in the Gulf of Mexico at the time (a record also later broken by Rita).[5]

Katrina made its second landfall at 6:10 a.m. CDT[5] on Monday, August 29 as a Category 3 hurricane with sustained winds of 125 mph (205 km/h) near Buras-Triumph, Louisiana. At landfall, hurricane-force winds extended outward 120 miles (190 km) from the center and the storm's central pressure was 920 mbar. After moving over southeastern Louisiana and Breton Sound, it made its third landfall near the Louisiana/Mississippi border with 120 mph (195 km/h) sustained winds, still at Category 3 intensity.[5]

Katrina maintained strength well into Mississippi, finally losing hurricane strength more than 150 miles (240 km) inland near Meridian, Mississippi. It was downgraded to a tropical depression near Clarksville, Tennessee, but its remnants were last distinguishable in the eastern Great Lakes region on August 31, when it was absorbed by a frontal boundary. The resulting extratropical storm moved rapidly to the northeast and affected eastern Canada.[5]

Preparations
Main article: Preparations for Hurricane Katrina
Federal government

Flanked by Michael Chertoff, Secretary of Homeland Security, left, and Secretary of Defense Donald Rumsfeld, President George W. Bush meets with members of the White House Task Force on Hurricane Katrina Recovery on August 31, 2005, in the Cabinet Room of the White House.On the morning of Friday, August 26, at 10 a.m. CDT (1500 UTC), Katrina had strengthened to a Category 3 storm in the Gulf of Mexico. Later that afternoon, the NHC realized that Katrina had yet to make the turn toward the Florida Panhandle and ended up revising the predicted track of the storm from the panhandle to the Mississippi coast.[12][13] The NHC issued a hurricane watch for southeastern Louisiana, including the New Orleans area at 10 a.m. CDT Saturday, August 27. That afternoon the NHC extended the watch to cover the Mississippi and Alabama coastlines as well as the Louisiana coast to Intracoastal City.

The United States Coast Guard began prepositioning resources beyond the expected impact zone starting on August 26, and activated more than 400 reservists.[14] Aircrews from the Aviation Training Center, in Mobile, staged rescue aircraft from Texas to Florida.[15] All aircraft were returning back towards the Gulf of Mexico by the afternoon of August 29. Air crews, many of whom lost their homes during the hurricane, began a round-the-clock rescue effort in New Orleans, and along the Mississippi and Alabama coastlines.[16]

President of the United States George W. Bush declared a state of emergency in selected regions of Louisiana, Alabama, and Mississippi on Saturday, the 27th, two days before the hurricane made landfall.[17] That same evening, the NHC upgraded the storm alert status from hurricane watch to hurricane warning over the stretch of coastline between Morgan City, Louisiana to the Alabama-Florida border, 12 hours after the watch alert had been issued, and also issued a tropical storm warning for the westernmost Florida Panhandle.[5]

During video conferences involving the president on August 28 and 29, the director of the National Hurricane Center, Max Mayfield, expressed concern that Katrina might push its storm surge over the city's levees and flood walls. In one conference, he stated, "I do not think anyone can tell you with confidence right now whether the levees will be topped or not, but that's obviously a very, very great concern."[18]

On Sunday, August 28, as the sheer size of Katrina became clear, the NHC extended the tropical storm warning zone to cover most of the Louisiana coastline and a larger portion of the Florida Panhandle. The National Weather Service's New Orleans/Baton Rouge office issued a vividly worded bulletin predicting that the area would be "uninhabitable for weeks" after "devastating damage" caused by Katrina, which at that time rivaled the intensity of Hurricane Camille.[19] "On Sunday, August 28, President Bush spoke with Governor Blanco to encourage her to order a mandatory evacuation of New Orleans." (Per page 235 of Special Report of the Committee on Homeland Security and Governmental Affairs)[20]

Voluntary and mandatory evacuations were issued for large areas of southeast Louisiana as well as coastal Mississippi and Alabama. About 1.2 million residents of the Gulf Coast were covered under a voluntary or mandatory evacuation order.[5]

Investigation of State of Emergency declaration
In a September 26, 2005 hearing, former FEMA chief Michael Brown testified before a U.S. House subcommittee about FEMA's response. During that hearing, Representative Stephen Buyer (R-IN) inquired as to why President Bush's declaration of state of emergency of August 27 had not included the coastal parishes of Orleans, Jefferson, and Plaquemines.[21] (In fact, the declaration did not include any of Louisiana's coastal parishes, whereas the coastal counties were included in the declarations for Mississippi[22] and Alabama.[23]) Brown testified that this was because Louisiana Governor Blanco had not included those parishes in her initial request for aid, a decision that he found "shocking." After the hearing, Blanco released a copy of her letter, which showed she had requested assistance for "all the southeastern parishes [but not by name] including the New Orleans Metropolitan area and the mid state Interstate I-49 corridor and northern parishes along the I-20 corridor that are accepting [evacuated citizens]."[24]

Gulf Coast

Radar image of Hurricane Katrina making landfall in LouisianaOn August 26, the state of Mississippi activated its National Guard in preparation for the storm's landfall. Additionally, the state government activated its Emergency Operations Center the next day, and local governments began issuing evacuation orders. By 7:00 p.m. EDT on August 28, 11 counties and eleven cities issued evacuation orders, a number which increased to 41 counties and 61 cities by the following morning. Moreover, 57 emergency shelters were established on coastal communities, with 31 additional shelters available to open if needed.[9] Louisiana's hurricane evacuation plan calls for local governments in areas along and near the coast to evacuate in three phases, starting with the immediate coast 50 hours before the start of tropical storm force winds. Persons in areas designated Phase II begin evacuating 40 hours before the onset of tropical storm winds and those in Phase III areas (including New Orleans) evacuate 30 hours before the start of such winds.[25]

Many private caregiving facilities that relied on bus companies and ambulance services for evacuation were unable to evacuate their charges because they waited too long. Rental cars were in short supply and many forms of public transportation had been shut down well before the storm arrived.[26] Some estimates claimed that 80% of the 1.3 million residents of the greater New Orleans metropolitan area evacuated, leaving behind substantially fewer people than remained in the city during the Hurricane Ivan evacuation.[27]

By Sunday, August 28, most infrastructure along the Gulf Coast had been shut down, including all Canadian National Railway and Amtrak rail traffic into the evacuation areas as well as the Waterford Nuclear Generating Station.[28] The NHC maintained the coastal warnings until late on August 29, by which time Hurricane Katrina was over central Mississippi.[5]

Greater New Orleans area
See also: Hurricane preparedness for New Orleans

Vertical cross-section of New Orleans, showing maximum levee height of 23 feet (7 m). Vertical scale exaggerated.By August 26, the possibility of unprecedented cataclysm was already being considered. Many of the computer models had shifted the potential path of Katrina 150 miles (240 km) westward from the Florida Panhandle, putting the city of New Orleans directly in the center of their track probabilities; the chances of a direct hit were forecast at 17%, with strike probability rising to 29% by August 28.[29] This scenario was considered a potential catastrophe because some parts of New Orleans and the metro area are below sea level. Since the storm surge produced by the hurricane's right-front quadrant (containing the strongest winds) was forecast to be 28 feet (8.5 m), emergency management officials in New Orleans feared that the storm surge could go over the tops of levees protecting the city, causing major flooding.[30]

At a news conference at 10 a.m. on August 28, shortly after Katrina was upgraded to a Category 5 storm, New Orleans mayor Ray Nagin ordered the first-ever mandatory evacuation of the city, calling Katrina "a storm that most of us have long feared."[31] The city government also established several "refuges of last resort" for citizens who could not leave the city, including the massive Louisiana Superdome, which sheltered approximately 26,000 people and provided them with food and water for several days as the storm came ashore.[32]

Florida
Many people living in the South Florida area were unaware when Katrina strengthened from a tropical storm to a hurricane in one day and struck southern Florida near the Miami-Dade – Broward county line. The hurricane struck between the cities of Aventura, in Miami-Dade County, and Hallandale, in Broward County, on Thursday, August 25, 2005. However, National Hurricane Center (NHC) forecasts had correctly predicted that Katrina would intensify to hurricane strength before landfall, and hurricane watches and warnings were issued 31.5 hours and 19.5 hours before landfall, respectively — only slightly less than the target thresholds of 36 and 24 hours.[5]

Florida Governor Jeb Bush declared a state of emergency on August 24 in advance of Hurricane Katrina's landfall in Florida. Shelters were opened and schools closed in several counties in the southern part of the state. A number of evacuation orders were also issued, mostly voluntary, although a mandatory evacuation was ordered for vulnerable housing in Martin County.[33]

Impact
Main article: Hurricane Katrina effects by region
Deaths by state Alabama 2
Florida 14
Georgia 2
Kentucky 1
Louisiana 1,577*
Mississippi 238
Ohio 2
Total 1,836
Missing 705
*Includes out-of-state evacuees
counted by Louisiana
On August 29, Katrina's storm surge caused 53 different levee breaches in greater New Orleans submerging eighty percent of the city. A June 2007 report by the American Society of Civil Engineers indicated that two-thirds of the flooding were caused by the multiple failures of the city's floodwalls.[34] Not mentioned were the flood gates that were not closed. The storm surge also devastated the coasts of Mississippi and Alabama, making Katrina the most destructive and costliest natural disaster in the history of the United States, and the deadliest hurricane since the 1928 Okeechobee Hurricane. The total damage from Katrina is estimated at $81.2 billion (2005 U.S. dollars), nearly double the cost of the previously most expensive storm, Hurricane Andrew, when adjusted for inflation.[5][35]

As of May 19, 2006, the confirmed death toll (total of direct and indirect deaths) stood at 1,836, mainly from Louisiana (1,577) and Mississippi (238).[1][2][36] However, 705 people remain categorized as missing in Louisiana,[37] and many of the deaths are indirect, but it is almost impossible to determine the exact cause of some of the fatalities.

Federal disaster declarations covered 90,000 square miles (233,000 km²) of the United States, an area almost as large as the United Kingdom. The hurricane left an estimated three million people without electricity. On September 3, 2005, Homeland Security Secretary Michael Chertoff described the aftermath of Hurricane Katrina as "probably the worst catastrophe, or set of catastrophes," in the country's history, referring to the hurricane itself plus the flooding of New Orleans.[38]

South Florida and Cuba

Damage to a mobile home in Davie, Florida following Hurricane KatrinaMain article: Effects of Hurricane Katrina in Florida
Hurricane Katrina first made landfall on August 25, 2005 in South Florida where it hit as a Category 1 hurricane, with 80 mph (130 km/h) winds. Rainfall was heavy in places and exceeded 14 inches (350 mm) in Homestead, Florida,[5] and a storm surge of 3 – 5 feet (1.5 m) was measured in parts of Monroe County.[35] More than 1 million customers were left without electricity, and damage in Florida was estimated from $1 – $2 billion, with most of the damage coming from flooding and overturned trees. There were 14 fatalities reported in Florida as a result of Hurricane Katrina.[5]

Most of the Florida Keys experienced tropical-storm force winds from Katrina as the storm's center passed to the north, with hurricane force winds reported in the Dry Tortugas. Rainfall was also high in the islands, with 10 inches (250 mm) falling on Key West. On August 26, a strong F1 tornado formed from an outer rain band of Katrina and struck Marathon. The tornado damaged a hangar at the airport there and caused an estimated $5 million in damage.[39]

Although Hurricane Katrina stayed well to the north of Cuba, on August 29 it brought tropical-storm force winds and rainfall of over 8 inches (200 mm) to western regions of the island. Telephone and power lines were damaged and around 8,000 people were evacuated in the Pinar del Río Province. According to Cuban television reports the coastal city of Surgidero de Batabano was 90% underwater.[40]

Louisiana

Flooding in Venice, LouisianaOn August 29, Hurricane Katrina made landfall near Buras-Triumph, Louisiana with 125 mph (205 km/h) winds, as a strong Category 3 storm. However, as it had only just weakened from Category 4 strength and the radius of maximum winds was large, it is possible that sustained winds of Category 4 strength briefly impacted extreme southeastern Louisiana. Although the storm surge to the east of the path of the eye in Mississippi was higher, a very significant surge affected the Louisiana coast. The height of the surge is uncertain because of a lack of data, although a tide gauge in Plaquemines Parish indicated a storm tide in excess of 14 feet (4.3 m) and a 12-foot (3 m) storm surge was recorded in Grand Isle. Hurricane Katrina made final landfall near the mouth of the Pearl River, with the eye straddling St. Tammany Parish, Louisiana and Hancock County, Mississippi, on the morning of August 29th at about 9:45M CST. [5]

Hurricane Katrina also brought heavy rain to Louisiana, with 8 – 10 inches (200 – 250 mm) falling on a wide swath of the eastern part of the state. In the area around Slidell, the rainfall was even higher, and the highest rainfall recorded in the state was approximately 15 inches (380 mm). As a result of the rainfall and storm surge the level of Lake Pontchartrain rose and caused significant flooding along its northeastern shore, affecting communities from Slidell to Mandeville. Several bridges were destroyed, including the I-10 Twin Span Bridge connecting Slidell to New Orleans.[5] Almost 900,000 people in Louisiana lost power as a result of Hurricane Katrina.[41]

Katrina’s storm surge inundated all parishes surrounding Lake Pontchartrain, including St. Tammany, Tangipahoa, St. John the Baptist and St. Charles Parishes. St. Tammany Parish received a two-part storm surge: First, as Lake Pontchartrain rose and the storm blew water from the Gulf of Mexico into the lake. Second, as the eye of Katrina passed, westerly winds pushed water into a bottleneck at the Rigolets Pass, forcing it farther inland. The range of surge levels in eastern St. Tammany Parish is estimated at 13 to 16 feet, not including wave action. [42]

Hard-hit St. Bernard Parish was flooded due to breaching of the levees that contained a navigation channel called the Mississippi River Gulf Outlet (MR-GO) and the breach of the Levee Board designed and built 40 Arpent canal levee. The search for the missing was undertaken by the St. Bernard Fire Department due to the assets of the United States Coast Guard being diverted to New Orleans. According to an interview in the New Orleans Times-Picayune, the coroner was still trying to get a list of missing from the Red Cross in November 2005. While there were some victims on this list whose bodies were found in their homes, the vast majority were tracked down through word-of-mouth and credit card records. As of December 2005, the official missing list in the Parish stood at 47.[43]

According to the U.S. Dept. of Housing and Urban Development, in St. Bernard Parish, 81% (20,229) of the housing units were damaged. In St. Tammany Parish, 70% (48,792) were damaged and in Placquemines Parish 80% (7,212) were damaged. [44]

New Orleans
Main articles: Effects of Hurricane Katrina in New Orleans and 2005 levee failures in Greater New Orleans

Flooded I-10/I-610/West End Blvd interchange and surrounding area of northwest New Orleans and Metairie, LouisianaAs the eye of Hurricane Katrina swept to the northeast, it subjected the city to hurricane conditions for hours. Although power failures prevented accurate measurement of wind speeds in New Orleans, there were a few measurements of hurricane-force winds. From this the NHC concluded that it is likely that much of the city experienced sustained winds of Category 1 or Category 2 strength.

Katrina's storm surge led to 53 levee breaches in the federally built levee system protecting metro New Orleans and the failure of the 40 Arpent Canal levee. Nearly every levee in metro New Orleans was breached as Hurricane Katrina passed just east of the city limits. Failures occurred in New Orleans and surrounding communities, especially St. Bernard Parish. The Mississippi River Gulf Outlet (MR-GO) breached its levees in approximately 20 places, flooding much of east New Orleans, most of Saint Bernard Parish and the East Bank of Plaquemines Parish. The major levee breaches in the city included breaches at the 17th Street Canal levee, the London Avenue Canal, and the wide, navigable Industrial Canal, which left approximately 80% of the city flooded.[45]

Most of the major roads traveling into and out of the city were damaged. The only routes out of the city were the westbound Crescent City Connection and the Huey P. Long Bridge, as large portions of the I-10 Twin Span Bridge traveling eastbound towards Slidell, Louisiana had collapsed. Both the Lake Pontchartrain Causeway and the Crescent City Connection only carried emergency traffic.[46]

On August 29, at 7:40 a.m. CDT, it was reported that most of the windows on the north side of the Hyatt Regency New Orleans had been blown out, and many other high rise buildings had extensive window damage.[47] The Hyatt was the most severely damaged hotel in the city, with beds reported to be flying out of the windows. Insulation tubes were exposed as the hotel's glass exterior was completely sheared off.[48]

A U.S. Coast Guardsman searches for survivors in New Orleans in the aftermath of KatrinaThe Superdome, which was sheltering many people who had not evacuated, sustained significant damage. Two sections of the Superdome's roof were compromised and the dome's waterproof membrane had essentially been peeled off. Louis Armstrong New Orleans International Airport was closed before the storm but did not flood. On August 30, it was reopened to humanitarian and rescue operations. Limited commercial passenger service resumed at the airport on September 13 and regular carrier operations resumed in early October.[49]

Levee breaches in New Orleans also caused widespread loss of life, with over 700 bodies recovered in New Orleans by October 23, 2005.[50] Some survivors and evacuees reported seeing dead bodies lying in city streets and floating in still-flooded sections, especially in the east of the city. The advanced state of decomposition of many corpses, some of which were left in the water or sun for days before being collected, hindered efforts by coroners to identify many of the dead.[51]

The first deaths reported from the city were reported shortly before midnight on August 28, as three nursing home patients died during an evacuation to Baton Rouge, most likely from dehydration. While there were also early reports of fatalities amid mayhem at the Superdome, only six deaths were confirmed there, with four of these originating from natural causes, one from a drug overdose, and one a suicide. At the Convention Center, four bodies were recovered. One of the four is believed to be the result of a homicide.[52]

Mississippi
Main article: Effects of Hurricane Katrina in Mississippi

U.S. Route 90's Bay St. Louis Bridge on Pass Christian was destroyed as a result of Katrina.The Gulf coast of Mississippi suffered massive damage from the impact of Hurricane Katrina on August 29, leaving 238 people dead, 67 missing, and billions of dollars in damage: bridges, barges, boats, piers, houses and cars were washed inland.[53] Katrina traveled up the entire state, and afterwards, all 82 counties in Mississippi were declared disaster areas for federal assistance, 47 for full assistance.[53]

After making a brief initial landfall in Louisiana, Katrina had made its final landfall near the state line, and the eyewall passed over the cities of Bay St. Louis and Waveland as a Category 3 hurricane with sustained winds of 120 mph (195 km/h).[5] Katrina's powerful right-front quadrant passed over the west and central Mississippi coast, causing a powerful 27-foot (8.2 m) storm surge, which penetrated 6 miles (10 km) inland in many areas and up to 12 miles (20 km) inland along bays and rivers; in some areas, the surge crossed Interstate 10 for several miles.[5] Hurricane Katrina brought strong winds to Mississippi, which caused significant tree damage throughout the state. The highest unofficial reported wind gust recorded from Katrina was one of 135 mph (217 km/h) in Poplarville, in Pearl River County.[5]

Damage to Long Beach, Mississippi following Hurricane KatrinaThe storm also brought heavy rains with 8 – 10 inches (200 – 250 mm) falling in southwestern Mississippi and rain in excess of 4 inches (100 mm) falling throughout the majority of the state. Katrina caused eleven tornadoes in Mississippi on August 29, some of which damaged trees and power lines.[5]

Battered by wind, rain and storm surge, some beachfront neighborhoods were completely leveled. Preliminary estimates by Mississippi officials calculated that 90% of the structures within half a mile of the coastline were completely destroyed,[54] and that storm surges traveled as much as six miles (10 km) inland in portions of the state's coast.[35] One apartment complex with approximately thirty residents seeking shelter inside collapsed. More than half of the 13 casinos in the state, which were floated on barges to comply with Mississippi land-based gambling laws, were washed hundreds of yards inland by waves.[54]

A number of streets and bridges were washed away. On U.S. Highway 90 along the Mississippi Gulf Coast, two major bridges were completely destroyed: the Bay St. Louis — Pass Christian[5] bridge, and the Biloxi - Ocean Springs bridge. In addition, the eastbound span of the I-10 bridge over the Pascagoula River estuary was damaged. In the weeks after the storm, with the connectivity of the coastal U.S. Highway 90 shattered, traffic traveling parallel to the coast was reduced first to State Road 11 (parallel to I-10) then to two lanes on the remaining I-10 span when it was opened.

Surge damage in Pascagoula, MississippiAll three coastal counties of the state were severely affected by the storm. Katrina's surge was the most extensive, as well as the highest, in the documented history of the United States; large portions of both Hancock, Harrison, and Jackson Counties were inundated by the storm surge, in all three cases affecting most of the populated areas.[55] Surge covered almost the entire lower half of Hancock County, destroying the coastal communities of Clermont Harbor and Waveland, much of Bay St. Louis, and flowed up the Jourdan River, flooding Diamondhead and Kiln. In Harrison County, Pass Christian was completely inundated, along with a narrow strip of land to the east along the coast, which includes the cities of Long Beach and Gulfport; the flooding was more extensive in communities such as D'Iberville, which borders Back Bay. Biloxi, on a peninsula between the Back Bay and the coast, was particularly hard hit, especially the low-lying Point Cadet area. In Jackson County, storm surge flowed up the wide river estuary, with the combined surge and freshwater flooding cutting the county in half. Remarkably, over 90% of Pascagoula, the easternmost coastal city in Mississippi, and about 75 miles (121 km) east of Katrina's landfall near the Louisiana-Mississippi border, was flooded from surge at the height of the storm. Other large Jackson County neighborhoods such as Porteaux Bay and Gulf Hills were severely damaged with large portions being completely destroyed, and St. Martin was hard hit; Ocean Springs, Moss Point, Gautier, and Escatawpa also suffered major surge damage.

Mississippi Emergency Management Agency officials also recorded deaths in Forrest, Hinds, Warren, and Leake counties. Over 900,000 people throughout the state experienced power outages.[41]

Southeast United States

Flood waters come up the steps of Mobile's federal courthouse.Although Hurricane Katrina made landfall well to the west, Alabama and the Florida Panhandle were both affected by tropical-storm force winds and a storm surge varying from 12 to 16 feet (3–5 m) around Mobile Bay,[5] with higher waves on top. Sustained winds of 67 mph (107 km/h) were recorded in Mobile, Alabama, and the storm surge there was approximately 12 feet (3.7 m).[5] The surge caused significant flooding several miles inland along Mobile Bay. Four tornadoes were also reported in Alabama.[5] Ships, oil rigs, boats and fishing piers were washed ashore along Mobile Bay: the cargo ship M/V Caribbean Clipper and many fishing boats were grounded at Bayou La Batre.

An oil rig under construction along the Mobile River broke its moorings and floated 1.5 miles (2 km) northwards before striking the Cochrane Bridge just outside Mobile. No significant damage resulted to the bridge and it was soon reopened. The damage on Dauphin Island was severe, with the surge destroying many houses and cutting a new canal through the western portion of the island. An offshore oil rig also became grounded on the island. As in Mississippi, the storm surge caused significant beach erosion along the Alabama coastline.[5] More than 600,000 people lost power in Alabama as a result of Hurricane Katrina and two people died in a traffic accident in the state. Residents in some areas, such as Selma, were without power for several days.[41]

Along the Florida Panhandle the storm surge was typically about five feet (1.5 m) and along the west-central Florida coast there was a minor surge of 1 – 2 feet (0.3 – 0.6 m). In Pensacola, Florida 56 mph (90 km/h) winds were recorded on August 29. The winds caused damage to some trees and structures and there was some minor flooding in the Panhandle. There were two indirect fatalities from Katrina in Walton County as a result of a traffic accident.[5] In the Florida Panhandle, 77,000 customers lost power.[56]

Bayou La Batre: cargo ship and fishing boats were groundedNorthern and central Georgia were affected by heavy rains and strong winds from Hurricane Katrina as the storm moved inland, with more than 3 inches (75 mm) of rain falling in several areas. At least 18 tornadoes formed in Georgia on August 29, the most on record in that state for one day in August. The most serious of these tornadoes was an F2 tornado which affected Heard County and Carroll County. This tornado caused 3 injuries and one fatality and damaged several houses. In addition this tornado destroyed several poultry barns, killing over 140,000 chicks. The other tornadoes caused significant damages to buildings and agricultural facilities. In addition to the fatality caused by the F2 tornado, there was another fatality in a traffic accident.[57]

Other U.S. States and Canada

Total rainfall from Katrina in the United States. Data for the New Orleans area are not available.Hurricane Katrina weakened as it moved inland, but tropical-storm force gusts were recorded as far north as Fort Campbell, Kentucky on August 30, and the winds damaged trees in New York. The remnants of the storm brought high levels of rainfall to a wide swath of the eastern United States, and rain in excess of 2 inches (50 mm) fell in parts of 20 states.[58] A number of tornadoes associated with Katrina formed on August 30 and August 31, which caused minor damages in several regions. In total, 62 tornadoes formed in eight states as a result of Katrina.[35]

Eastern Arkansas received light rain from the passage of Katrina.[59] Gusty winds downed some trees and power lines, though damage was minimal.[60] In Kentucky, a storm that had moved through the weekend before had already produced flooding and the rainfall from Katrina added to this. As a result of the flooding, Kentucky Governor Ernie Fletcher declared three counties disaster areas and a statewide state of emergency.[61][62] One person was killed in Hopkinsville, Kentucky and part of a high school collapsed.[63] Flooding also prompted a number of evacuations in West Virginia and Ohio, the rainfall in Ohio leading to two indirect deaths. Katrina also caused a number of power outages in many areas, with over 100,000 customers affected in Tennessee, primarily in the Memphis and Nashville areas.[64]

The remnants of Katrina were absorbed by a new cyclone to its east across Pennsylvania. This second cyclone continued north and affected Canada on August 31. In Ontario there were a few isolated reports of rain in excess of 100 mm (4 inches) and there were a few reports of damage from fallen trees.[65] Flooding also occurred in both Ontario and Quebec, cutting off a number of isolated villages in Quebec, particularly in the Côte-Nord region.[66]

Aftermath
See also: Social effects of Hurricane Katrina, Political effects of Hurricane Katrina, Hurricane Katrina disaster relief, and IDPs in the United States
Economic effects
Costliest U.S. Atlantic hurricanes
Cost refers to total estimated property damage. Rank Hurricane Season Cost (2008 USD)
1 Katrina 2005 $89.6 billion
2 Andrew 1992 $40.7 billion
3 Ike 2008 $24.0 billion
4 Wilma 2005 $22.7 billion
5 Charley 2004 $18.6 billion
Main article: List of costliest Atlantic hurricanes
Main article: Economic effects of Hurricane Katrina
The economic effects of the storm were far-reaching. As of April 2006, the Bush Administration has sought $105 billion for repairs and reconstruction in the region,[67] and this does not account for damage to the economy caused by potential interruption of the oil supply, destruction of the Gulf Coast's highway infrastructure, and exports of commodities such as grain. Katrina damaged or destroyed 30 oil platforms and caused the closure of nine refineries;[35] the total shut-in oil production from the Gulf of Mexico in the six-month period following Katrina was approximately 24% of the annual production and the shut-in gas production for the same period was about 18%.[68] The forestry industry in Mississippi was also affected, as 1.3 million acres (5,300 km²) of forest lands were destroyed.[69] The total loss to the forestry industry from Katrina is calculated to rise to about $5 billion.[69] Furthermore, hundreds of thousands of local residents were left unemployed, which will have a trickle-down effect as fewer taxes are paid to local governments. Before the hurricane, the region supported approximately one million non-farm jobs, with 600,000 of them in New Orleans. It is estimated that the total economic impact in Louisiana and Mississippi may exceed $150 billion.[70]

Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, which became the largest diaspora in the history of the United States.[71] Houston, Texas, had an increase of 35,000 people; Mobile, Alabama, gained over 24,000; Baton Rouge, Louisiana, over 15,000; and Hammond, Louisiana received over 10,000, nearly doubling its size. Chicago received over 6,000 people, the most of any non-southern city.[72] By late January, 2006, about 200,000 people were once again living in New Orleans, less than half of the pre-storm population.[73] By July 1, 2006, when new population estimates were calculated by the U.S. Census Bureau, the state of Louisiana showed a population decline of 219,563, or 4.87%.[74] Additionally, some insurance companies have stopped insuring homeowners in the area because of the high costs from Hurricanes Katrina and Rita, or have raised homeowners' insurance premiums to cover their risk.[75]

Environmental effects
See also: Murphy Oil Spill (Chalmette, Louisiana)

The Chandeleur Islands, before Katrina (left) and after (right), showing the impact of the storm along coastal areas.Katrina also had a profound impact on the environment. The storm surge caused substantial beach erosion, in some cases completely devastating coastal areas. In Dauphin Island, approximately 90 miles (150 km) to the east of the point where the hurricane made landfall, the sand that comprised the barrier island was transported across the island into the Mississippi Sound, pushing the island towards land.[76] The storm surge and waves from Katrina also obliterated the Chandeleur Islands, which had been affected by Hurricane Ivan the previous year.[77] The US Geological Survey has estimated 217 square miles (560 km2) of land was transformed to water by the hurricanes Katrina and Rita.[78]

The lands that were lost were breeding grounds for marine mammals, brown pelicans, turtles, and fish, as well as migratory species such as redhead ducks.[69] Overall, about 20% of the local marshes were permanently overrun by water as a result of the storm.[69]

The damage from Katrina forced the closure of 16 National Wildlife Refuges. Breton National Wildlife Refuge lost half its area in the storm.[79] As a result, the hurricane affected the habitats of sea turtles, Mississippi sandhill cranes, Red-cockaded woodpeckers and Alabama Beach mice.[79]

Finally, as part of the cleanup effort, the flood waters that covered New Orleans were pumped into Lake Pontchartrain, a process that took 43 days to complete.[35] These residual waters contained a mix of raw sewage, bacteria, heavy metals, pesticides, toxic chemicals, and about 6.5 million U.S. gallons (24.6 million L) of oil, which has sparked fears in the scientific community of massive numbers of fish dying.[69]

Prior to the storm, subsidence and erosion caused erosion in the Louisiana wetlands and bayous. This, along with the canals built in the area, allowed for Katrina to maintain more of its intensity when it struck.[80]

Looting and violence
Further information: Effects of Hurricane Katrina on New Orleans

A Border Patrol Special Response Team searches a hotel room-by-room in New Orleans in response to Hurricane Katrina.Shortly after the hurricane moved away on August 30, 2005, some residents of New Orleans who remained in the city began looting stores. Many were in search of food and water that were not available to them through any other means, as well as non-essential items.[81]

Reports of carjacking, murders, thefts, and rapes in New Orleans flooded the news. Some sources later determined that many of the reports were innaccurate, because of the confusion.[82] Thousands of National Guard and federal troops were mobilized (the total went from 7,841 in the area the day Katrina hit to a maximum of 46,838 on September 10) and sent to Louisiana along with numbers of local law enforcement agents from across the country who were temporarily deputized by the state. "They have M16s and are locked and loaded. These troops know how to shoot and kill and I expect they will," Louisiana Governor Kathleen Blanco said. Congressman Bill Jefferson (D-LA) told ABC News: "There was shooting going on. There was sniping going on. Over the first week of September, law and order were gradually restored to the city."[83] Several shootings were between police and New Orleans residents, including a fatal incident at Danziger Bridge.[84]

A number of arrests were made throughout the affected area, including some near the New Orleans Convention Center. A temporary jail was constructed of chain link cages in the city train station.[85]

In Texas, where more than 300,000 refugees were located, local officials ran 20,000 criminal background checks on the refugees, as well as on the relief workers helping them and people who opened up their homes. The background checks found that 45% of the refugees had a criminal record of some nature, and that 22% had a violent criminal record.[86] The number of homicides in Houston from September 2005 through February 22, 2006 went up by 23% relative to the same period a year before; 29 of the 170 murders involved displaced Louisianans as a victim or as a suspect.[87]

Government response

President Bush stands with Secretary of Defense Donald Rumsfeld, Secretary of Labor Elaine Chao and Secretary of Health and Human Services Mike Leavitt during a press conference from the Rose Garden, regarding the devastation along the Gulf Coast caused by Katrina.
-President Bush watching the flooded areas from Air Force One.Within the United States and as delineated in the National Response Plan, disaster response and planning is first and foremost a local government responsibility. When local government exhausts its resources, it then requests specific additional resources from the county level. The request process proceeds similarly from the county to the state to the federal government as additional resource needs are identified. Many of the problems that arose developed from inadequate planning and back-up communications systems at various levels.[88]

Some disaster recovery response to Katrina began before the storm, with Federal Emergency Management Agency (FEMA) preparations that ranged from logistical supply deployments to a mortuary team with refrigerated trucks. A network of volunteers began rendering assistance to local residents and residents emerging from New Orleans and surrounding parishes as soon as the storm made landfall (even though many were directed to not enter the area), and continued for more than six months after the storm.[88]

Of the 60,000 people stranded in New Orleans, the Coast Guard rescued more than 33,500.[89] Congress recognized the Coast Guard's response with an official entry in the Congressional Record,[90] and the Armed Service was awarded the Presidential Unit Citation.[91]

The United States Northern Command established Joint Task Force (JTF) Katrina based out of Camp Shelby, Mississippi, to act as the military's on-scene command on Sunday, August 28.[92] Approximately 58,000 National Guard personnel were activated to deal with the storm's aftermath, with troops coming from all 50 states.[93] The Department of Defense also activated volunteer members of the Civil Air Patrol.

Michael Chertoff, Secretary of the Department of Homeland Security, decided to take over the federal, state, and local operations officially on August 30, 2005, citing the National Response Plan.[94] This was refused by Governor Blanco who indicated that her National Guard could manage. Early in September, Congress authorized a total of $62.3 billion in aid for victims.[95] Additionally, President Bush enlisted the help of former presidents Bill Clinton and George H.W. Bush to raise additional voluntary contributions, much as they did after the 2004 Indian Ocean earthquake and tsunami.[96] American flags were also ordered to be half-staff from September 2, 2005 to September 20, 2005 in honor of the victims.[97]

FEMA provided housing assistance (rental assistance, trailers, etc.) to more than 700,000 applicants—families and individuals. However, only one-fifth of the trailers requested in Orleans Parish have been supplied, resulting in an enormous housing shortage in the city of New Orleans.[98] Many local areas voted to not allow the trailers, and many areas had no utilities, a requirement prior to placing the trailers. To provide for additional housing, FEMA has also paid for the hotel costs of 12,000 individuals and families displaced by Katrina through February 7, 2006, when a final deadline was set for the end of hotel cost coverage. After this deadline, evacuees were still eligible to receive federal assistance, which could be used towards either apartment rent, additional hotel stays, or fixing their ruined homes, although FEMA no longer paid for hotels directly.[99] As of early July 2006, there are still about 100,000 people living in 37,745 FEMA-provided trailers.[100]

Law enforcement and public safety agencies, from across the United States, provided a "mutual aid" response to Louisiana and New Orleans in the weeks following the disaster. Many agencies responded with manpower and equipment from as far away as California, Michigan, Nevada, New York, and Texas. This response was welcomed by local Louisiana authorities as their staff were either becoming fatigued, stretched too thin, or even quitting from the job.[101]

Two weeks after the storm, more than half of the states were involved in providing shelter for evacuees. By four weeks after the storm, evacuees had been registered in all 50 states and in 18,700 zip codes—half of the nation's residential postal zones. Most evacuees had stayed within 250 miles (400 km), but 240,000 households went to Houston and other cities over 250 miles (400 km) away and another 60,000 households went over 750 miles (1,200 km) away.[102]

Criticism of government response

USNS Comfort takes on supplies at Mayport, Florida en route to the Gulf Coast.Main article: Criticism of government response to Hurricane Katrina
The criticisms of the government's response to Hurricane Katrina primarily consisted of condemnations of mismanagement and lack of leadership in the relief efforts in response to the storm and its aftermath. More specifically, the criticism focused on the delayed response to the flooding of New Orleans, and the subsequent state of chaos in the Crescent City.[52] The neologism Katrinagate was coined to refer to this controversy, and was a runner-up for "2005 word of the year."[103]

Within days of Katrina's August 29, 2005 landfall, public debate arose about the local, state and federal governments' role in the preparations for and response to the hurricane. Criticism was initially prompted by televised images of visibly shaken and frustrated political leaders, and of residents who remained stranded by flood waters without water, food or shelter. Deaths from thirst, exhaustion, and violence, days after the storm had passed, fueled the criticism, as did the dilemma of the evacuees at facilities such as the Louisiana Superdome (designed to handle 800, yet 30,000 arrived)and the New Orleans Civic Center (not designed as an evacuation center, yet 25,000 arrived). Some alleged that race, class, and other factors could have contributed to delays in government response. The percentage of black victims among storm-related deaths (49%)[104] was below their proportion in the area's population (approx. 60%[105] ).

In accordance with federal law, President George W. Bush directed the Secretary of the Department of Homeland Security, Michael Chertoff, to coordinate the Federal response. Chertoff designated Michael D. Brown, head of the Federal Emergency Management Agency, as the Principal Federal Official to lead the deployment and coordination of all federal response resources and forces in the Gulf Coast region. However, the President and Secretary Chertoff initially came under harsh criticism for what some perceived as a lack of planning and coordination, even though Governor Blanco resisted their efforts. Eight days later, Brown was recalled to Washington and Coast Guard Vice Admiral Thad W. Allen replaced him as chief of hurricane relief operations.[106] Three days after the recall, Michael D. Brown resigned as director of FEMA in spite of having received recent praise from President Bush.[107]

On September 2, 2005, during a benefit concert for Hurricane Katrina relief on NBC, A Concert for Hurricane Relief, Kanye West was a featured speaker. Controversy arose when West was presenting, as he deviated from the prepared script:

I hate the way they portray us in the media. You see a black family, it says, 'They're looting.' You see a white family, it says, 'They're looking for food.' And, you know, it's been five days [waiting for federal help] because most of the people are black. And even for me to complain about it, I would be a hypocrite because I've tried to turn away from the teacher-the TV because it's too hard to watch. I've even been shopping before even giving a donation, so now I'm calling my business manager right now to see what is the biggest amount I can give, and just to imagine if I was down there, and those are my people down there. So anybody out there that wants to do anything that we can help — with the way America is set up to help the poor, the black people, the less well-off, as slow as possible. I mean, the Red Cross is doing everything they can. We already realize a lot of people that could help are at war right now, fighting another way — and they've given them permission to go down and shoot us!

Mike Myers, with whom West was paired to present, spoke next and continued as normal by reading the script. Once it was his turn to speak again, West added, "George Bush doesn't care about black people." Although the camera quickly cut away to Chris Tucker, West's comments still reached the East Coast broadcasts, and were replayed and discussed afterwards.[108]

Criticism from politicians, activists, pundits and journalists of all stripes was directed at the local and state and governments headed by Mayor Ray Nagin of New Orleans and Louisiana Governor Kathleen Blanco. Nagin and Blanco were criticized for failing to implement New Orleans' evacuation plan and for ordering residents to a shelter of last resort without any provisions for food, water, security, or sanitary conditions. Perhaps the most important criticism of Nagin was that he delayed his emergency evacuation order until 19 hours before landfall, which led to hundreds of deaths of people who (by that time) could not find any way out of the city.[9]

The destruction wrought by Hurricane Katrina raised other, more general public policy issues about emergency management, environmental policy, poverty, and unemployment. The discussion of both the immediate response and of the broader public policy issues may have affected elections and legislation enacted at various levels of government. The storm's devastation also prompted a Congressional investigation, which found that FEMA and the Red Cross "did not have a logistics capacity sophisticated enough to fully support the massive number of Gulf coast victims." Additionally, it placed responsibility for the disaster on all three levels of government.[9]

An ABC News Poll conducted on September 2, 2005, showed slightly more blame was being directed at state and local governments (75%) than at the Federal government (67%), with 44% blaming Bush's leadership directly.[109] A later CNN/USAToday/Gallup poll showed that respondents disagreed widely on who was to blame for the problems in the city following the hurricane — 13% said Bush, 18% said federal agencies, 25% blamed state or local officials and 38% said no one was to blame.[110]

International response
Main article: International response to Hurricane Katrina

United States Navy personnel unload Canadian relief supplies from a Canadian Air Force transport aircraft in Pensacola, Florida.Over seventy countries pledged monetary donations or other assistance. Notably, Cuba and Venezuela (both hostile to US government themselves) were the first countries to offer assistance, pledging over $1 million, several mobile hospitals, water treatment plants, canned food, bottled water, heating oil, 1,100 doctors and 26.4 metric tons of medicine, though this aid was rejected by the U.S. government.[111][112][113][114] Kuwait made the largest single pledge, $500 million; other large donations were made by Qatar and United Arab Emirates (each $100 million), South Korea ($30 million), Australia ($10 million), India, China (both $5 million), New Zealand ($2 million),[115] Pakistan ($1.5 million),[116] and Bangladesh ($1 million).[117]

India sent tarps, blankets and hygiene kits. An Indian Air Force IL-76 aircraft delivered 25 tonnes of relief supplies for the Hurricane Katrina victims at the Little Rock Air Force Base, Arkansas on September 13, 2005.

Israel sent an IDF delegation to New Orleans to transport aid equipment including 80 tons of food, disposable diapers, beds, blankets, generators and additional equipment which were donated from different governmental institutions, civilian institutions and the IDF.[118] The Bush Administration announced in mid-September that it did not need Israeli divers and physicians to come to the United States for search and rescue missions, but a small team landed in New Orleans on September 10 to give assistance to operations already under way. The team administered first aid to survivors, rescued abandoned pets and discovered hurricane victims.[119]

Countries like Sri Lanka, which was still recovering from the Indian Ocean Tsunami, also offered to help. Countries including Canada, Mexico, Singapore, and Germany sent supplies, relief personnel, troops, ships and water pumps to aid in the disaster recovery. Belgium sent in a team of relief personnel. Britain's donation of 350,000 emergency meals did not reach victims because of laws regarding mad cow disease.[120] Russia's initial offer of two jets was declined by the U.S. State Department but accepted later. The French offer was also declined and requested later.[121]

Despite receiving aid from around the world, there was also a heavy dose of criticism from around the world, including accusations of racism that were revealed at the international level across global press. Quotations from the UK Mirror such as "Many things about the United States are wonderful, but it has a vile underbelly which is usually kept well out of sight. Now in New Orleans it has been exposed to the world." were common.[122]

Non-governmental organization response
Most intense landfalling Atlantic hurricanes in the United States
based on size and intensity for total points on the Hurricane Severity Index Rank Hurricane Year Intensity Size Total
1 Carla 1961 17 25 42
2 Hugo 1989 16 24 40
Betsy 1965 15 25 40
4 Camille 1969 22 14 36
Katrina 2005 13 23 36
Opal 1995 11 25 36
7 Miami 1926 15 19 34
8 Audrey 1957 17 16 33
Fran 1996 11 22 33
Wilma 2005 12 21 33
Source: Hurricane Severity Index
The American Red Cross, Southern Baptist Convention, Salvation Army, Oxfam, Common Ground Collective, Emergency Communities, Habitat for Humanity, Catholic Charities, Service International, "A River of Hope" and many other charitable organizations provided help to the victims of the storm. They were not allowed into New Orleans proper by the National Guard for several days after the storm because of safety concerns. These organizations raised US$4.25 billion in donations by the public, with the Red Cross receiving over half of the donations.[123]

Volunteers from amateur radio's emergency service wing, the Amateur Radio Emergency Service, provided communications in areas where the communications infrastructure had been damaged or totally destroyed, relaying everything from 911 traffic to messages home.[124] In Hancock County, Mississippi, ham radio operators provided the only communications into or out of the area, and even served as 911 dispatchers.[125]

Many corporations also contributed to relief efforts. On September 13, 2005, it was reported that corporate donations to the relief effort were $409 million, and were expected to exceed $1 billion.[126]

During and after the Hurricanes Katrina, Wilma and Rita, the American Red Cross had opened 1,470 different shelters across and registered 3.8 million overnight stays. None were allowed in New Orleans however. A total of 244,000 Red Cross workers (95% of which were non-paid volunteers) were utilized throughout these three hurricanes. In addition, 346,980 comfort kits (such as toothpaste, soap, washcloths and toys for children) and 205,360 cleanup kits (containing brooms, mops and bleach) were distributed. For mass care, the organization served 68 million snacks and meals to victims of the disasters and to rescue workers. The Red Cross also had its Disaster Health services meet 596,810 contacts, and Disaster Mental Health services met 826,590 contacts. Red Cross emergency financial assistance was provided to 1.4 million families. Hurricane Katrina was the first natural disaster in the United States in which the American Red Cross utilized its "Safe and Well" family location website.[127][128]

In the year following Katrina's strike on the Gulf Coast, The Salvation Army allocated donations of more than $365 million to serve more than 1.7 million people in nearly every state. The organization's immediate response to Hurricane Katrina included more than 5.7 million hot meals served in and around New Orleans, 8.3 million sandwiches, snacks & drinks. Its SATERN network of amateur radio operators picked up where modern communications left off to help locate more than 25,000 survivors. Salvation Army pastoral care counselors were on hand to comfort the emotional and spiritual needs of 277,000 individuals. As part of the overall effort, Salvation Army officers, employees and volunteers contributed more than 900,000 hours of service.[129]

Domino's Pizza gave away free pizza to anyone with a badge in downtown New Orleans for months after Katrina[citation needed].

Analysis of New Orleans levee failures
Main article: 2005 levee failures in Greater New Orleans

View of the eyewall of Hurricane Katrina taken on August 28, 2005, as seen from a NOAA WP-3D hurricane hunter aircraft before the storm made landfall on the United States Gulf Coast.A June 2007 report released by the American Society of Civil Engineers states that the failures of the locally built and federally funded levees in New Orleans were found to be primarily the result of system design flaws.[34] The US Army Corps of Engineers who by federal mandate is responsible for the conception, design and construction of the region's flood-control system failed to pay sufficient attention to public safety. The Levee Boards had hamstrung the Army Corps.

According to new modeling and field observations by a team from Louisiana State University, the Mississippi River Gulf Outlet (MRGO), a 200-meter-wide (660-foot-wide) canal designed to provide a shortcut from New Orleans to the Gulf of Mexico, helped provide a funnel for the storm surge, making it 20% higher and 100%-200% faster as it crashed into the city. St. Bernard Parish, one of the more devastated areas, lies just south of the MRGO. The Army Corps of Engineers disputes this causality and maintains Katrina would have overwhelmed the levees with or without the contributing effect of the MRGO.[130] The water flowing west from the storm surge was perpendicular to MRGO, and thus the canal had a negligible effect.

On April 5, 2006, months after independent investigators had demonstrated that levee failures were not caused by natural forces beyond intended design strength, Lieutenant General Carl Strock testified before the United States Senate Subcommittee on Energy and Water that "We have now concluded we had problems with the design of the structure."[131] He also testified that the U.S. Army Corps of Engineers did not know of this mechanism of failure prior to August 29, 2005. The claim of ignorance is refuted, however, by the National Science Foundation investigators hired by the Army Corps of Engineers, who point to a 1986 study by the Corps itself that such separations were possible in the I-wall design.[132] As the levee walls were mandated by the Levee Boards and were designed by local firms under the control of the Levee Boards, the Army Corps had little choice. The Army Corps had recommended 72 foot pilings be used, yet the Leveee Boards argued and prevailed that 24 foot pilings would be sufficient.

Various conspiracy theories began floating around that the levees were in fact deliberately demolished. A number of New Orleans residents described hearing "explosions" coming from the Industrial Canal levee in the Lower 9th Ward before the floodwaters rushed in. A National Guard worker claims he was sworn to secrecy upon finding explosives residue at the site of the break.[133] The fracture of the wall due to a barge hitting it would also be an explanation of the loud noise heard.

Many of the levees have been reconstructed since the time of Katrina. In reconstructing them, precautions were taken to bring the levees up to modern building code standards and to ensure their safety. For example, in every situation possible, the Corps of Engineers replaced I-walls with T-walls. T-walls have a horizontal concrete base that protects against soil erosion underneath the floodwalls.[134]

However, there are funding battles over the remaining levee improvements. In February 2008, the Bush administration requested that the state of Louisiana pay about $1.5 billion of an estimated $7.2 billion for Army Corps of Engineers levee work, a proposal which angered many Louisiana leaders.[135]

On May 2, 2008, Louisiana Gov. Bobby Jindal used a speech to The National Press Club to request that President Bush free up money to complete work on Louisiana's levees. Bush promised to include the levee funding in his 2009 budget, but rejected the idea of including the funding in a war bill, which would pass sooner.[136]

Media involvement
Main article: Media coverage of Hurricane Katrina

Geraldo Rivera reporting from the New Orleans Convention Center on September 2, 2005.Many representatives of the news media reporting on the aftermath of Hurricane Katrina became directly involved in the unfolding events, instead of simply reporting. Because of the loss of most means of communication, such as land-based and cellular telephone systems, field reporters in many cases became conduits for information between victims and authorities.

The authorities, who monitored local and network news broadcasts, as well as internet sites, would then attempt to coordinate rescue efforts based on the reports. One illustration was when Geraldo Rivera of Fox News tearfully pleaded for authorities to either send help or evacuate the thousands of evacuees stranded at the Ernest N. Morial Convention Center.[137]

The storm also brought a dramatic rise in the role of Internet sites - especially blogging and community journalism. One example was the effort of NOLA.com, the web affiliate of New Orleans' Times-Picayune, which was awarded the Breaking News Pulitzer Prize,[138] and shared the Public Service Pulitzer with the Biloxi-based Sun Herald.[139] The newspaper's coverage was carried for days only on NOLA's blogs, as the newspaper lost its presses and evacuated its building as water rose around it on August 30. The site became an international focal point for news by local media, and also became a vital link for rescue operations and later for reuniting scattered residents, as it accepted and posted thousands of individual pleas for rescue on its blogs and forums. NOLA was monitored constantly by an array of rescue teams — from individuals to the Coast Guard — which used information in rescue efforts. Much of this information was relayed from trapped victims via the SMS functions of their cell phones, to friends and relatives outside the area, who then relayed the information back to NOLA.com. The aggregation of community journalism, user photos and the use of the internet site as a collaborative response to the storm attracted international attention, and was called a watershed moment in journalism.[140] In the wake of these online-only efforts, the Pulitzer Committee for the first time opened all its categories to online entries.[141]

The role of AM radio was of importance to the hundreds of thousands of persons with no other ties to news. AM radio provided emergency information regarding access to assistance for hurricane victims. Immediately after Hurricane Katrina, radio station WWL-AM (New Orleans) was one of the few area radio stations in the area remaining on the air. The 870 kHz frequency has a clear channel high power designation and the on-going nighttime broadcasts continued to be available up to 500 miles (800 km) away. Announcers continued to broadcast from improvised studio facilities after the storm damaged their transmitter tower.[citation needed]

During the period of several weeks when most area radio stations were off the air, WWL-AM's emergency coverage was simulcast on the frequencies of other area radio stations. This emergency service was named "The United Radio Broadcasters of New Orleans." To reach emergency radio operators in storm-ravaged areas, many of whom made their volunteer services available to the Red Cross and government entities, WWL-AM was simulcast on shortwave outlet WHRI, owned by World Harvest Radio International. The cellular phone antenna network was severely damaged and completely inoperable for several months.

As the U.S. military and rescue services regained control over the city, there were restrictions on the activity of the media. On September 9, the military leader of the relief effort announced that reporters would have "zero access" to efforts to recover bodies in New Orleans. Immediately following this announcement, CNN filed a lawsuit and obtained a temporary restraining order against the ban. The next day the government backed down and reversed the ban.[142]

Hurricane Katrina has also been the centerpiece of several documentary films, including Spike Lee's film, When the Levees Broke, and Darren Martinez's film, Hellp.[143] An episode of the Fox TV series House first broadcast on May 16, 2006, featured a teenage victim of Hurricane Katrina at the center of the main medical storyline.

cyclone

2009-10-24T06:29:00.000-07:00

In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth[1][2]. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth.

Large-scale cyclonic circulations are almost always centred on areas of low atmospheric pressure[3][4]. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Subtropical cyclones are of intermediate size.[5][6] Cyclones have also been seen on other planets outside of the Earth, such as Mars and Neptune.[7][8]

Cyclogenesis describes the process of cyclone formation and intensification [9]. Extratropical cyclones form as waves in large regions of enhanced midlatitude temperature contrasts called baroclinic zones. These zones contract to form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, cyclones occlude as cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the polar or subtropical jetstream.

Weather fronts separate two masses of air of different densities and are associated with the most prominent meteorological phenomena. Air masses separated by a front may differ in temperature or humidity. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines. They form west of the circulation center and generally move from west to east. Warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. They move poleward ahead of the cyclone path. Occluded fronts form late in the cyclone life cycle near the enter of the cyclone and often wrap around the storm center.

Tropical cyclogenesis describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.[10] Cyclones can transition between extratropical, subtropical, and tropical phases under the right conditions. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[11] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[12]

Contents [hide]
1 Structure
2 Formation
3 Types
3.1 Polar cyclone
3.2 Polar low
3.3 Extratropical
3.4 Subtropical
3.5 Tropical
3.6 Mesoscale
4 References
5 External links

[edit] Structure
There are a number of structural characteristics common to all cyclones. As they are low pressure areas, their center is the area of lowest atmospheric pressure in the region, often known in mature tropical cyclones as the eye.[13] Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure.[14] The wind flow around a large cyclone is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis effect.[15] (An anticyclone, on the other hand, rotates clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere.)

[edit] Formation

The initial extratropical low pressure area forms at the location of the red dot on the image. It is usually perpendicular (at a right angle to) the leaf-like cloud formation seen on satellite during the early stage of cyclogenesis. The location of the axis of the upper level jet stream is in light blue.Main articles: Cyclogenesis and Tropical cyclogenesis
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area).[9] Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale. Extratropical cyclones form as waves along weather fronts before occluding later in their life cycle as cold core cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.[10] Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[11] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[12] Cyclogenesis is the opposite of cyclolysis, and has an anticyclonic (high pressure system) equivalent which deals with the formation of high pressure areas—Anticyclogenesis.[16]

The surface low has a variety of ways of forming. Topography can force a surface low when dense low-level high pressure system ridges in east of a north-south mountain barrier.[17] Mesoscale convective systems can spawn surface lows which are initially warm core.[18] The disturbance can grow into a wave-like formation along the front and the low will be positioned at the crest. Around the low, flow will become cyclonic, by definition. This rotational flow will push polar air equatorward west of the low via its trailing cold front, and warmer air with push poleward low via the warm front. Usually the cold front will move at a quicker pace than the warm front and “catch up” with it due to the slow erosion of higher density airmass located out ahead of the cyclone and the higher density airmass sweeping in behind the cyclone, usually resulting in a narrowing warm sector.[19] At this point an occluded front forms where the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal.[20]

Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a positive feedback loop over warm ocean waters.[21]Tropical cyclogenesis is the technical term describing the development and strengthening of a tropical cyclone in the atmosphere.[22] The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear.[23] An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the Saffir-Simpson Hurricane Scale).[24]

Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("wind shear") sets parts of the lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm is then thought to draw up this spinning air, tilting the rolls' orientation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column. Mesocyclones are normally relatively localized: they lie between the synoptic scale (hundreds of kilometers) and microscale (hundreds of meters). Radar imagery is used to identify these features.[25] The eye of the storm is usually calm and collected.

[edit] Types
There are six main types of cyclones: Polar cyclones, Polar lows, Extratropical cyclones, Subtropical cyclones, Tropical cyclones, and Mesocyclones

[edit] Polar cyclone
Main article: Polar cyclone
A polar, sub-polar, or Arctic cyclone (also known as a polar vortex)[26] is a vast area of low pressure which strengthens in the winter and weakens in the summer.[27] A polar cyclone is a low pressure weather system, usually spanning 1,000 kilometres (620 mi) to 2,000 kilometres (1,200 mi), in which the air circulates in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. In the Northern Hemisphere, the polar cyclone has two centers on average. One center lies near Baffin Island and the other over northeast Siberia.[26] In the southern hemisphere, it tends to be located near the edge of the Ross ice shelf near 160 west longitude.[28] When the polar vortex is strong, westerly flow descends to the Earth's surface. When the polar cyclone is weak, significant cold outbreaks occur.[29]

[edit] Polar low
Main article: Polar low
A polar low is a small-scale, short-lived atmospheric low pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than 1,000 kilometres (620 mi) and exist for no more than a couple of days. They are part of the larger class of mesoscale weather systems. Polar lows can be difficult to detect using conventional weather reports and are a hazard to high-latitude operations, such as shipping and gas and oil platforms. Polar lows have been referred to by many other terms, such as polar mesoscale vortex, Arctic hurricane, Arctic low, and cold air depression. Today the term is usually reserved for the more vigorous systems that have near-surface winds of at least 17 m/s.[30]

[edit] Extratropical

A fictitious synoptic chart of an extratropical cyclone affecting the UK and Ireland. The blue arrows between isobars indicate the direction of the wind, while the "L" symbol denotes the centre of the "low". Note the occluded, cold and warm frontal boundaries.Main article: Extratropical cyclone
An extratropical cyclone is a synoptic scale low pressure weather system that has neither tropical nor polar characteristics, being connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones".[31]

The descriptor "extratropical" refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" where extratropical transition has occurred,[31][32] and are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena which along with anti-cyclones, drive the weather over much of the Earth.

Although extratropical cyclones are almost always classified as baroclinic since they form along zones of temperature and dewpoint gradient within the westerlies, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform with radius.[33] An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection, which warms its core.[10]

[edit] Subtropical

Subtropical Storm Andrea in 2007Main article: Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form between the equator and the 50th parallel.[34] As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical cyclones or extratropical cyclones, and used terms such as quasi-tropical and semi-tropical to describe the cyclone hybrids.[35] By 1972, the National Hurricane Center officially recognized this cyclone category.[36] Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002.[34] They have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones, and exist in areas of weak to moderate temperature gradient.[34]

Since they form from initially extratropical cyclones which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required for their formation are lower than the tropical cyclone threshold by three degrees Celsius, or five degrees Fahrenheit, lying around 23 degrees Celsius.[37] This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.[38]

[edit] Tropical

Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004Main article: Tropical cyclone
A tropical cyclone is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.[10]

The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in Maritime Tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on their location and strength, tropical cyclones are referred to by other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply as a cyclone. Generally speaking, a tropical cyclone is referred to as a hurricane (from the name of the ancient Central American deity of wind, Huracan) in the Atlantic basin, and a Cyclone in the Pacific.[39]

While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge.[40] They develop over large bodies of warm water,[41] and lose their strength if they move over land.[42] This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions.[43] They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere.

Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses;[10] From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.[44]

[edit] Mesoscale

A mesocyclone from the Greensburg, Kansas tornado indicated on Doppler weather radar.Main article: Mesocyclone
A mesocyclone is a vortex of air, approximately 2 kilometres (1.2 mi) to 10 kilometres (6.2 mi) in diameter (the mesoscale of meteorology), within a convective storm.[45] Air rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a severe thunderstorm.[46] Such storms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, where tornadoes may form. About 1700 mesocyclones form annually across the United States, but only half produce tornadoes.[11]

Cyclone on Mars, imaged by the Hubble Space TelescopeCyclones are not unique to Earth. Cyclonic storms are common on Jovian planets, like the Small Dark Spot on Neptune. Also known as the Wizard's Eye, it is about one third the diameter of the Great Dark Spot. It received the name "Wizard's Eye" because it looks like an eye. This appearance is caused by a white cloud in the middle of the Wizard's Eye.[8] Mars has also exhibited cyclonic storms.[7] Jovian storms like the Great Red Spot are usually mistakenly named as giant hurricanes or cyclonic storms. However, this is inaccurate, as the Great Red Spot is, in fact, the inverse phenomenon, an anticyclone.

Tornado

2009-10-24T02:26:00.000-07:00

A tornado near Anadarko, Oklahoma. The tornado itself is the thin tube reaching from the cloud to the ground. The lower part of this tornado is surrounded by a translucent dust cloud, kicked up by the tornado's strong winds at the surface.A tornado is a violent, dangerous, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust.

Most tornadoes have wind speeds between 40 mph (64 km/h) and 110 mph (177 km/h), are approximately 250 feet (75 m) across, and travel a few miles (several kilometers) before dissipating. Some attain wind speeds of more than 300 mph (480 km/h), stretch more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 km).[1][2][3]

Although tornadoes have been observed on every continent except Antarctica, the vast majority of tornadoes in the world occur in the United States, and specifically, in the Tornado Alley region of the country.[4] They also commonly occur in southern Canada, south-central and eastern Asia, the Philippines, east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand.[5]

Contents [hide]
1 Etymology
2 Definitions
2.1 Tornado
2.2 Funnel cloud
2.3 Tornado family
2.4 Tornado outbreak
3 Types
3.1 True tornadoes
3.2 Tornado-like circulations
4 Characteristics
4.1 Shape
4.2 Size
4.3 Appearance
4.4 Rotation
4.5 Sound and seismology
4.6 Electromagnetic, lightning, and other effects
5 Life cycle
5.1 Supercell relationship
5.2 Formation
5.3 Maturity
5.4 Demise
6 Intensity and damage
7 Climatology
7.1 Associations with climate and climate change
8 Detection
8.1 Storm spotting
8.1.1 Visual evidence
8.2 Radar
9 Extremes
10 Safety
11 Myths and misconceptions
12 Ongoing research
13 See also
14 References
15 Further reading
16 External links

Part of the Nature series on
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Etymology
The word tornado is an altered form of the Spanish word tronada, which means "thunderstorm." This in turn was taken from the Latin tonare, meaning "to thunder". It most likely reached its present form through a combination of the Spanish tronada and tornar ("to turn"); however, this may be a folk etymology.[6][7] A tornado is also commonly referred to as a twister, and is also sometimes referred to by the old-fashioned colloquial term cyclone.[8] The term "cyclone" is used as a synonym for "tornado" in the often-aired 1939 film, The Wizard of Oz. The term "twister" is also used in that film, along with being the title of the 1996 film Twister.

Definitions

A tornado near Seymour, Texas
This tornado has no funnel cloud; however, the rotating dust cloud indicates that strong winds are occurring at the surface, and thus it is a true tornado. This picture was taken in Louisville, Kentucky.Tornado
The Glossary of Meteorology defines a tornado as "a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud..."[9] In practice, for a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a complete definition of the word; for example, there is disagreement as to whether separate touchdowns of the same funnel constitute separate tornadoes.[3] "Tornado" refers to the vortex of wind, not the condensation cloud.[10][11]

Funnel cloud
Main article: funnel cloud
A tornado is not necessarily visible; however, the intense low pressure caused by the high wind speeds (see Bernoulli's principle) and rapid rotation (due to cyclostrophic balance) usually causes water vapor in the air to become visible as a funnel cloud or condensation funnel.[12]

There is some disagreement over the definition of "funnel cloud" and "condensation funnel". According to the Glossary of Meteorology, a funnel cloud is any rotating cloud pendant from a cumulus or cumulonimbus, and thus including most tornadoes under this definition.[13] Among many meteorologists, a funnel cloud is strictly defined as a rotating cloud which is not associated with strong winds at the surface, and a "condensation funnel" is a broad term for any rotating cloud below a cumuliform cloud.[3]

Tornadoes often begin as funnel clouds with no associated strong winds at the surface, however, not all of these evolve into a tornado. However, many tornadoes are preceded by a funnel cloud. Most tornadoes produce strong winds at the surface while the visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud and a tornado from a distance.[3]

Tornado family
Main article: tornado family
Occasionally, a single storm will produce more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm are referred to as a tornado family.[14]

Tornado outbreak
Main articles: tornado outbreak and tornado outbreak sequence
Occasionally, several tornadoes are spawned from the same large-scale storm system. If there is no break in activity, this is considered a tornado outbreak, although there are various definitions. A period of several successive days with tornado outbreaks in the same general area (spawned by multiple weather systems) is a tornado outbreak sequence, occasionally called an extended tornado outbreak.[9][15][16]

Types

A multiple-vortex tornado outside of Dallas, Texas on April 2, 1957True tornadoes
Multiple vortex tornado
Main article: multiple vortex tornado
A multiple vortex tornado is a type of tornado in which two or more columns of spinning air rotate around a common center. Multivortex structure can occur in almost any circulation, but is very often observed in intense tornadoes. These vortices often create small areas of heavier damage along the main tornado path.[3][10]

Satellite tornado
A satellite tornado is a term for a weaker tornado which forms very near a large, strong tornado contained within the same mesocyclone. The satellite tornado may appear to "orbit" the larger tornado (hence the name), giving the appearance of one, large multi-vortex tornado. However, a satellite tornado is a distinct funnel, and is much smaller than the main funnel.[3]

Waterspout

A waterspout near the Florida KeysMain article: waterspout
A waterspout is defined by the National Weather Service simply as a tornado over water. However, researchers typically distinguish "fair weather" waterspouts from tornadic waterspouts. Fair weather waterspouts are less severe but far more common, and are similar in dynamics to dust devils and landspouts. They form at the bases of cumulus congestus cloud towers in tropical and semitropical waters. They have relatively weak winds, smooth laminar walls, and typically travel very slowly, if at all. They occur most commonly in the Florida Keys and in the northern Adriatic Sea.[17][18][19] Tornadic waterspouts are more literally "tornadoes over water". They can form over water like mesocyclonic tornadoes, or be a land tornado which crosses onto water. Since they form from severe thunderstorms and can be far more intense, faster, and longer-lived than fair weather waterspouts, they are considered far more dangerous.[20]

Landspout

A landspout near North Platte, Nebraska on May 22, 2004Main article: landspout
A landspout (officially known as a dust-tube tornado) is a tornado not associated with a mesocyclone. The name stems from their characterization as essentially a "fair weather waterspout on land". Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel which often does not reach the ground. Landspouts also create a distinctively laminar cloud of dust when they make contact with the ground, due to their differing mechanics from true mesoform tornadoes. Though usually weaker than classic tornadoes, they still produce strong winds and may cause serious damage.[3][10]

Tornado-like circulations
Gustnado
Main article: gustnado
A gustnado (gust front tornado) is a small, vertical swirl associated with a gust front or downburst. Because they are technically not associated with the cloud base, there is some debate as to whether or not gustnadoes are actually tornadoes. They are formed when fast moving cold, dry outflow air from a thunderstorm is blown through a mass of stationary, warm, moist air near the outflow boundary, resulting in a "rolling" effect (often exemplified through a roll cloud). If low level wind shear is strong enough, the rotation can be turned horizontally (or diagonally) and make contact with the ground. The result is a gustnado.[3][21] They usually cause small areas of heavier rotational wind damage among areas of straight-line wind damage. It is also worth noting that since they are absent of any Coriolis influence from a mesocyclone, they seem to be alternately cyclonic and anticyclonic without preference.

Dust devil

A dust devil in NevadaMain article: dust devil
A dust devil resembles a tornado in that it is a vertical swirling column of air. However, they form under clear skies and are rarely as strong as even the weakest tornadoes. They form when a strong convective updraft is formed near the ground on a hot day. If there is enough low level wind shear, the column of hot, rising air can develop a small cyclonic motion that can be seen near the ground. They are not considered tornadoes because they form during fair weather and are not associated with any actual cloud. However, they can, on occasion, result in major damage, especially in arid areas.[22][23]

Fire whirl
Main article: fire whirl
Tornado-like circulations occasionally occur near large, intense wildfires and are called fire whirls. They are not considered tornadoes except in the rare case where they connect to a pyrocumulus or other cumuliform cloud above. Fire whirls usually are not as strong as tornadoes associated with thunderstorms. However, they can produce significant damage.[15]

Steam devil
Main article: steam devil
A steam devil is a term describing a rotating updraft that involves steam or smoke. A steam devil is very rare, but they mainly form from smoke emitting from a power plant smokestack. Hot springs and deserts may also be suitable locations for a steam devil to form. There have also been reports of cold air steam devils as well.

Snow Devil
A snow devil is a swirling vortex with a updraft that forms on snow or ice. This usually forms in places such as Jackson Hole or other mountain areas. Sometimes strong snow devils may form a white rope tornado in association with a cloudmass.

Whirlpools
Main article: Whirlpool
A whirlpool is a swirling vortex that may or may not have a downdraft that forms in liquid, mainly water. A whirlpool usually forms in drains when some kind of swirl starts in the water and some kind of opening forms and gives it a downdraft. Whirlpool may also form in tides, when two powerful waves in opposite directions run parallel to each other or directly below a waterspout but it strength depends on the waterspouts strength however it is rare for this to happen.

Characteristics

A wedge tornado, nearly a mile wide. This tornado hit Binger, Oklahoma.
A rope tornado in its dissipating stage. Tecumseh, OKShape
Most tornadoes take on the appearance of a narrow funnel, a few hundred yards (a few hundred meters) across, with a small cloud of debris near the ground. However, tornadoes can appear in many shapes and sizes.

Small, relatively weak landspouts may only be visible as a small swirl of dust on the ground. Although the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 40 mph (64 km/h), the circulation is considered a tornado.[10] A tornado with a nearly cylindrical profile and relative low height is sometimes referred to as a stovepipe tornado. Large single-vortex tornadoes can look like large wedges stuck into the ground, and so are known as wedge tornadoes or wedges. The stovepipe classification is also used for this type of tornado, if it otherwise fits that profile. A wedge can be so wide that it appears to be a block of dark clouds, wider than the distance from the cloud base to the ground. Even experienced storm observers may not be able to tell the difference between a low-hanging cloud and a wedge tornado from a distance. Many, but not all major tornadoes are wedges.[24]

Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often curl or twist into complex shapes. These tornadoes are said to be roping out, or becoming a rope tornado. Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or may be completely obscured by condensation, dust, and debris, appearing to be a single funnel.[25]

In addition to these appearances, tornadoes may be obscured completely by rain or dust. These tornadoes are especially dangerous, as even experienced meteorologists might not spot them.[22]

Size
In the United States, on average tornadoes are around 500 feet (150 m) across, and stay on the ground for 5 miles (8 km).[22] Yet, there is an extremely wide range of tornado sizes, even for typical tornadoes. Weak tornadoes, or strong but dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet across. A tornado was once reported to have a damage path only 7 feet (2 m) long.[22] On the other end of the spectrum, wedge tornadoes can have a damage path a mile (1.6 km) wide or more. A tornado that affected Hallam, Nebraska on May 22, 2004 was at one point 2.5 miles (4 km) wide at the ground.[2]

In terms of path length, the Tri-State Tornado, which affected parts of Missouri, Illinois, and Indiana on March 18, 1925, was officially on the ground continuously for 219 miles (352 km). Many tornadoes which appear to have path lengths of 100 miles (160 km) or longer are actually a family of tornadoes which have formed in quick succession; however, there is no substantial evidence that this occurred in the case of the Tri-State Tornado.[15] In fact, modern reanalysis of the path suggests that the tornado began 15 miles (24 km) further west than previously thought.[26]

Appearance
Tornadoes can have a wide range of colors, depending on the environment in which they form. Those which form in a dry environment can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels which pick up little or no debris can be gray to white. While traveling over a body of water as a waterspout, they can turn very white or even blue. Funnels which move slowly, ingesting a lot of debris and dirt, are usually darker, taking on the color of debris. Tornadoes in the Great Plains can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning brilliantly white.[22]

Photographs of the Waurika, Oklahoma tornado of May 30, 1976, taken at nearly the same time by two photographers. In the top picture, the tornado is front-lit, with the sun behind the east-facing camera, so the funnel appears nearly white. In the lower image, where the camera is facing the opposite direction, the tornado is back-lit, with the sun behind the clouds.[27]Lighting conditions are a major factor in the appearance of a tornado. A tornado which is "back-lit" (viewed with the sun behind it) appears very dark. The same tornado, viewed with the sun at the observer's back, may appear gray or brilliant white. Tornadoes which occur near the time of sunset can be many different colors, appearing in hues of yellow, orange, and pink.[8][28]

Dust kicked up by the winds of the parent thunderstorm, heavy rain and hail, and the darkness of night are all factors which can reduce the visibility of tornadoes. Tornadoes occurring in these conditions are especially dangerous, since only weather radar observations, or possibly the sound of an approaching tornado, serve as any warning to those in the storm's path. Fortunately most significant tornadoes form under the storm's rain-free base, or the area under the thunderstorm's updraft, where there is little or no rain. In addition, most tornadoes occur in the late afternoon, when the bright sun can penetrate even the thickest clouds.[15] Also, night-time tornadoes are often illuminated by frequent lightning.

There is mounting evidence, including Doppler On Wheels mobile radar images and eyewitness accounts, that most tornadoes have a clear, calm center with extremely low pressure, akin to the eye of tropical cyclones. This area would be clear (possibly full of dust), have relatively light winds, and be very dark, since the light would be blocked by swirling debris on the outside of the tornado. Lightning is said to be the source of illumination for those who claim to have seen the interior of a tornado.[29][30][31]

Rotation
Tornadoes normally rotate cyclonically in direction (counterclockwise in the northern hemisphere, clockwise in the southern). While large-scale storms always rotate cyclonically due to the Coriolis effect, thunderstorms and tornadoes are so small that the direct influence of the Coriolis effect is inconsequential, as indicated by their large Rossby numbers. Supercells and tornadoes rotate cyclonically in numerical simulations even when the Coriolis effect is neglected.[32][33] Low-level mesocyclones and tornadoes owe their rotation to complex processes within the supercell and ambient environment.[34]

Approximately 1% of tornadoes rotate in an anticyclonic direction. Typically, only landspouts and gustnadoes rotate anticyclonically, and usually only those which form on the anticyclonic shear side of the descending rear flank downdraft in a cyclonic supercell.[35] However, on rare occasions, anticyclonic tornadoes form in association with the mesoanticyclone of an anticyclonic supercell, in the same manner as the typical cyclonic tornado, or as a companion tornado—either as a satellite tornado or associated with anticyclonic eddies within a supercell.[36]

Sound and seismology
Tornadoes emit widely on the acoustics spectrum and the sounds are caused by multiple mechanisms. Various sounds of tornadoes have been reported throughout time, mostly related to familiar sounds for the witness and generally some variation of a whooshing roar. Popularly reported sounds include a freight train, rushing rapids or waterfall, a jet engine from close proximity, or combinations of these. Many tornadoes are not audible from much distance; the nature and propagation distance of the audible sound depends on atmospheric conditions and topography.

The winds of the tornado vortex and of constituent turbulent eddies, as well as airflow interaction with the surface and debris, contribute to the sounds. Funnel clouds also produce sounds. Funnel clouds and small tornadoes are reported as whistling, whining, humming, or the buzzing of innumerable bees or electricity, or more or less harmonic, whereas many tornadoes are reported as a continuous, deep rumbling, or an irregular sound of “noise”.[37]

Since many tornadoes are audible only in very close proximity, sound is not reliable warning of a tornado. And, any strong, damaging wind, even a severe hail volley or continuous thunder in a thunderstorm may produce a roaring sound.[38]

An illustration of generation of infrasound in tornadoes by the Earth System Research Laboratory's Infrasound ProgramTornadoes also produce identifiable inaudible infrasonic signatures.[39]

Unlike audible signatures, tornadic signatures have been isolated; due to the long distance propagation of low-frequency sound, efforts are ongoing to develop tornado prediction and detection devices with additional value in understanding tornado morphology, dynamics, and creation.[40] Tornadoes also produce a detectable seismic signature, and research continues on isolating it and understanding the process.[41]

Electromagnetic, lightning, and other effects

A tornado and lightning in the Florida Keys.Tornadoes emit on the electromagnetic spectrum[42], for example, with sferics and E-field effects detected.[40][43] Little is yet understood, however.

Observed, also, are correlations with patterns of lightning activity, but these are not yet well understood. Tornadic storms do not contain more lightning than other storms and some tornadic cells never produce lightning. More often than not, overall cloud-to-ground (CG) lightning activity decreases as a tornado reaches the surface and returns to the baseline level when the tornado lifts. In many cases, very intense tornadoes and thunderstorms exhibit an increased and anomalous dominance of positive polarity CG discharges.[44] Electromagnetics and lightning have little or nothing to do directly with what drives tornadoes (tornadoes are basically a thermodynamic phenomenon), although there are likely connections with the storm and environment affecting both phenomena.

Luminosity has been reported in the past and is probably due to misidentification of external light sources such as lightning, city lights, and power flashes from broken lines, as internal sources are now uncommonly reported and are not known to ever have been recorded.

In addition to winds, tornadoes also exhibit changes in atmospheric variables such as temperature, moisture, and pressure. For example, on June 24, 2003 near Manchester, South Dakota, a probe measured a 100 mbar (hPa) (2.95 inHg) pressure deficit. The pressure dropped gradually as the vortex approached then dropped extremely rapidly to 850 mbar (hPa) (25.10 inHg) in the core of the violent tornado before rising rapidly as the vortex moved away, resulting in a V-shape pressure trace. Temperature tends to decrease and moisture content to increase in the immediate vicinity of a tornado.[45]

Life cycle

A sequence of images showing the birth of a tornado. First, the rotating cloud base lowers. This lowering becomes a funnel, which continues descending while winds build near the surface, kicking up dust and other debris. Finally, the visible funnel extends to the ground, and the tornado begins causing major damage. This tornado, near Dimmitt, Texas, was one of the best-observed violent tornadoes in history.Further information: Tornadogenesis
Supercell relationship
See also: Supercell
Tornadoes often develop from a class of thunderstorms known as supercells. Supercells contain mesocyclones, an area of organized rotation a few miles up in the atmosphere, usually 1–6 miles (2–10 km) across. Most intense tornadoes (EF3 to EF5 on the Enhanced Fujita Scale) develop from supercells. In addition to tornadoes, very heavy rain, frequent lightning, strong wind gusts, and hail are common in such storms.

Most tornadoes from supercells follow a recognizable life cycle.[10] That begins when increasing rainfall drags with it an area of quickly descending air known as the rear flank downdraft (RFD). This downdraft accelerates as it approaches the ground, and drags the supercell's rotating mesocyclone towards the ground with it.

Formation
As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating wall cloud. As the funnel descends, the RFD also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud becomes a tornado within minutes of the RFD reaching the ground.

Maturity
Initially, the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the mature stage. This can last anywhere from a few minutes to more than an hour, and during that time a tornado often causes the most damage, and in rare cases can be more than one mile (1.6 km) across. Meanwhile, the RFD, now an area of cool surface winds, begins to wrap around the tornado, cutting off the inflow of warm air which feeds the tornado.

Demise
As the RFD completely wraps around and chokes off the tornado's air supply, the vortex begins to weaken, and become thin and rope-like. This is the dissipating stage; often lasting no more than a few minutes, after which the tornado fizzles. During this stage the shape of the tornado becomes highly influenced by the winds of the parent storm, and can be blown into fantastic patterns.[15][27][28] Even though the tornado is dissipating, the tornado is still capable of causing damage. The storm is contracting into a rope-like tube and, like the ice skater who pulls her arms in to spin faster, winds can increase at this point.

As the tornado enters the dissipating stage, its associated mesocyclone often weakens as well, as the rear flank downdraft cuts off the inflow powering it. In particularly intense supercells tornadoes can develop cyclically. As the first mesocyclone and associated tornado dissipate, the storm's inflow may be concentrated into a new area closer to the center of the storm. If a new mesocyclone develops, the cycle may start again, producing one or more new tornadoes. Occasionally, the old (occluded) mesocyclone and the new mesocyclone produce a tornado at the same time.

Though this is a widely accepted theory for how most tornadoes form, live, and die, it does not explain the formation of smaller tornadoes, such as landspouts, long-lived tornadoes, or tornadoes with multiple vortices. These each have different mechanisms which influence their development—however, most tornadoes follow a pattern similar to this one.[46]

Intensity and damage

An example of EF1 damage. Here, the roof has been substantially damaged, and the garage door blown outwards, but the walls and supporting structures are still intact.Main article: Tornado intensity and damage
The Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. The Enhanced Fujita Scale was an upgrade to the older Fujita scale, with engineered (by expert elicitation) wind estimates and better damage descriptions, but was designed so that a tornado rated on the Fujita scale would receive the same numerical rating. An EF0 tornado will probably damage trees but not substantial structures, whereas an EF5 tornado can rip buildings off their foundations leaving them bare and even deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes. Doppler radar data, photogrammetry, and ground swirl patterns (cycloidal marks) may also be analyzed to determine intensity and award a rating.

Tornadoes vary in intensity regardless of shape, size, and location, though strong tornadoes are typically larger than weak tornadoes. The association with track length and duration also varies, although longer track tornadoes tend to be stronger.[47] In the case of violent tornadoes, only a small portion of the path is of violent intensity, most of the higher intensity from subvortices.[15]

In the United States, 80% of tornadoes are EF0 and EF1 (T0 through T3) tornadoes. The rate of occurrence drops off quickly with increasing strength—less than 1% are violent tornadoes(EF4, T8 or stronger).[48]

Outside the United States, areas in south-central Asia, and perhaps portions of southeastern South America and southern Africa, violent tornadoes are extremely rare. This is apparently mostly due to the lesser number of tornadoes overall, as research shows that tornado intensity distributions are fairly similar worldwide. A few significant tornadoes occur annually in Europe, Asia, southern Africa, and southeastern South America, respectively.[49]

Climatology
Main article: Tornado climatology

Areas worldwide where tornadoes are most likely, indicated by orange shading
Intense tornado activity in the United States. The darker-colored areas denote the area commonly referred to as Tornado Alley.The United States has the most tornadoes of any country, about four times more than estimated in all of Europe, not including waterspouts.[50] This is mostly due to the unique geography of the continent. North America is a relatively large continent that extends from the tropical south into arctic areas, and has no major east-west mountain range to block air flow between these two areas. In the middle latitudes, where most tornadoes of the world occur, the Rocky Mountains block moisture and atmospheric flow, allowing drier air at mid-levels of the troposphere, and causing cyclogenesis downstream to the east of the mountains. The desert Southwest also feeds drier air and the dry line, while the Gulf of Mexico fuels abundant low-level moisture. This unique topography allows for many collisions of warm and cold air, the conditions that breed strong, long-lived storms many times a year. A large portion of these tornadoes form in an area of the central United States known as Tornado Alley.[4] This area extends into Canada, particularly Ontario and the Prairie Provinces. Strong tornadoes also occasionally occur in northern Mexico.

The United States averages about 1,200 tornadoes per year. The Netherlands has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.0013 per sq mi (0.00048 per km²), annually), followed by the UK (around 33, or 0.00035 per sq mi (0.00013 per km²), per year),[51][52] but most are small and cause minor damage. In absolute number of events, ignoring area, the UK experiences more tornadoes than any other European country, excluding waterspouts.[50]

Tornadoes kill about 179 people per year in Bangladesh, by far the most in the world. This is due to high population density, poor quality of construction, lack of tornado safety knowledge, and other factors.[53][54] Other areas of the world that have frequent tornadoes include South Africa, parts of Argentina, Paraguay, and southern Brazil, as well as portions of Europe, Australia and New Zealand, and far eastern Asia.[5][55]

Tornadoes are most common in spring and least common in winter.[15] Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes can also be caused by landfalling tropical cyclones, which tend to occur in the late summer and autumn. But favorable conditions can occur at any time of the year.

Tornado occurrence is highly dependent on the time of day, because of solar heating.[56] Worldwide, most tornadoes occur in the late afternoon, between 3 pm and 7 pm local time, with a peak near 5 pm.[57][58][59][60][61] However, destructive tornadoes can occur at any time of day. The Gainesville Tornado of 1936, one of the deadliest tornadoes in history, occurred at 8:30 am local time.[15]

Associations with climate and climate change
Associations to various climate and environmental trends exist. For example, an increase in the sea surface temperature of a source region (e.g. Gulf of Mexico and Mediterranean Sea) increases atmospheric moisture content. Increased moisture can fuel an increase in severe weather and tornado activity, particularly in the cool season.[62]

Although insufficient support exists to make conclusions, some evidence does suggest that the Southern Oscillation is weakly correlated with changes in tornado activity; which vary by season and region as well as whether the ENSO phase is that of El Niño or La Niña.[63]

Climatic shifts may affect tornadoes via teleconnections in shifting the jet stream and the larger weather patterns. The climate-tornado link is confounded by the forces affecting larger patterns and by the local, nuanced nature of tornadoes. Although it is reasonable that global warming may affect trends in tornado activity[64], any such effect is not yet identifiable due to the complexity, local nature of the storms, and database quality issues. Any effect would vary by region.[65]

Detection
Main article: Convective storm detection

A Doppler radar image indicating the likely presence of a tornado over DeLand, Florida. Green colors indicate areas where the precipitation is moving towards the radar dish, while red areas are moving away. In this case the radar is in the bottom right corner of the image. Strong mesocyclones show up as adjacent areas of bright green and bright red, and usually indicate an imminent or occurring tornado. When these bright colors are one against the other on a radar display when in association with rotation, it is called a Tornado vortex signature.Rigorous attempts to warn of tornadoes began in the United States in the mid-20th century. Before the 1950s, the only method of detecting a tornado was by someone seeing it on the ground. Often, news of a tornado would reach a local weather office after the storm.

However, with the advent of weather radar, areas near a local office could get advance warning of severe weather. The first public tornado warnings were issued in 1950 and the first tornado watches and convective outlooks in 1952. In 1953 it was confirmed that hook echoes are associated with tornadoes[66]. By recognizing these radar signatures, meteorologists could detect thunderstorms probably producing tornadoes from dozens of miles away.[67]

Storm spotting
In the mid 1970s, the U.S. National Weather Service (NWS) increased its efforts to train storm spotters to spot key features of storms which indicate severe hail, damaging winds, and tornadoes, as well as damage itself and flash flooding. The program was called Skywarn, and the spotters were local sheriff's deputies, state troopers, firefighters, ambulance drivers, amateur radio operators, civil defense (now emergency management) spotters, storm chasers, and ordinary citizens. When severe weather is anticipated, local weather service offices request that these spotters look out for severe weather, and report any tornadoes immediately, so that the office can issue a timely warning.

Usually spotters are trained by the NWS on behalf of their respective organizations, and report to them. The organizations activate public warning systems such as sirens and the Emergency Alert System, and forward the report to the NWS.[68] There are more than 230,000 trained Skywarn weather spotters across the United States.[69]

In Canada, a similar network of volunteer weather watchers, called Canwarn, helps spot severe weather, with more than 1,000 volunteers.[70] In Europe, several nations are organizing spotter networks under the auspices of Skywarn Europe[71] and the Tornado and Storm Research Organisation (TORRO) has maintained a network of spotters in the United Kingdom since the 1970s.

Storm spotters are needed because radar systems such as NEXRAD do not detect a tornado; only indications of one. Radar may give a warning before there is any visual evidence of a tornado or imminent tornado, but ground truth from an observer can either verify the threat or determine that a tornado is not imminent. The spotter's ability to see what radar cannot is especially important as distance from the radar site increases, because the radar beam becomes progressively higher in altitude further away from the radar, chiefly due to curvature of Earth, and the beam also spreads out. Therefore, when far from a radar, only high in the storm is observed and the important areas are not sampled, and data resolution also suffers. Also, some meteorological situations leading to tornadogenesis are not readily detectable by radar and on occasion tornado development may occur more quickly than radar can complete a scan and send the batch of data.

Visual evidence

A rotating wall cloud with rear flank downdraft clear slot evident to its left rear. Taken on June 2, 1984 in OklahomaStorm spotters are trained to discern whether a storm seen from a distance is a supercell. They typically look to its rear, the main region of updraft and inflow. Under the updraft is a rain-free base, and the next step of tornadogenesis is the formation of a rotating wall cloud. The vast majority of intense tornadoes occur with a wall cloud on the backside of a supercell.[48]

Evidence of a supercell comes from the storm's shape and structure, and cloud tower features such as a hard and vigorous updraft tower, a persistent, large overshooting top, a hard anvil (especially when backsheared against strong upper level winds), and a corkscrew look or striations. Under the storm and closer to where most tornadoes are found, evidence of a supercell and likelihood of a tornado includes inflow bands (particularly when curved) such as a "beaver tail", and other clues such as strength of inflow, warmth and moistness of inflow air, how outflow- or inflow-dominant a storm appears, and how far is the front flank precipitation core from the wall cloud. Tornadogenesis is most likely at the interface of the updraft and rear flank downdraft, and requires a balance between the outflow and inflow.[10]

Only wall clouds that rotate spawn tornadoes, and usually precede the tornado by five to thirty minutes. Rotating wall clouds are the visual manifestation of a mesocyclone. Barring a low-level boundary, tornadogenesis is highly unlikely unless a rear flank downdraft occurs, which is usually visibly evidenced by evaporation of cloud adjacent to a corner of a wall cloud. A tornado often occurs as this happens or shortly after; first, a funnel cloud dips and in nearly all cases by the time it reaches halfway down, a surface swirl has already developed, signifying a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes may also occur without wall clouds, under flanking lines, and on the leading edge. Spotters watch all areas of a storm, and the cloud base and surface.[72]

Radar
Today, most developed countries have a network of weather radars, which remains the main method of detecting signatures probably associated with tornadoes. In the United States and a few other countries, Doppler radar stations are used. These devices measure the velocity and radial direction (towards or away from the radar) of the winds in a storm, and so can spot evidence of rotation in storms from more than a hundred miles (160 km) away.

Also, most populated areas on Earth are now visible from the Geostationary Operational Environmental Satellites (GOES), which aid in the nowcasting of tornadic storms.[70]

Extremes
Main article: Tornado records
The most extreme tornado in recorded history was the Tri-State Tornado, which roared through parts of Missouri, Illinois, and Indiana on March 18, 1925. It was likely an F5, though tornadoes were not ranked on any scale in that era. It holds records for longest path length (219 miles, 352 km), longest duration (about 3.5 hours), and fastest forward speed for a significant tornado (73 mph, 117 km/h) anywhere on earth. In addition, it is the deadliest single tornado in United States history (695 dead).[15] It was also the second costliest tornado in history at the time, but has been surpassed by several others non-normalized. When costs are normalized for wealth and inflation, it still ranks third today.[73]

The deadliest tornado in world history was the Daultipur-Salturia Tornado in Bangladesh on April 26, 1989, which killed approximately 1300 people.[53] Bangladesh has had at least 19 tornadoes in its history kill more than 100 people, almost half of the total in the rest of the world.

A map of the tornado paths in the Super OutbreakThe most extensive tornado outbreak on record, in almost every category, was the Super Outbreak, which affected a large area of the central United States and extreme southern Ontario in Canada on April 3 and April 4, 1974. Not only did this outbreak feature an incredible 148 tornadoes in only 18 hours, but an unprecedented number of them were violent; six were of F5 intensity, and twenty-four F4. This outbreak had a staggering sixteen tornadoes on the ground at the same time at the peak of the outbreak. More than 300 people, possibly as many as 330, were killed by tornadoes during this outbreak.[74]

While it is nearly impossible to directly measure the most violent tornado wind speeds (conventional anemometers would be destroyed by the intense winds), some tornadoes have been scanned by mobile Doppler radar units, which can provide a good estimate of the tornado's winds. The highest wind speed ever measured in a tornado, which is also the highest wind speed ever recorded on the planet, is 301 ± 20 mph (484 ± 32 km/h) in the F5 Moore, Oklahoma tornado. Though the reading was taken about 100 feet (30 m) above the ground, this is a testament to the power of the strongest tornadoes.[1]

Storms which produce tornadoes can feature intense updrafts, sometimes exceeding 150 mph (240 km/h). Debris from a tornado can be lofted into the parent storm and carried a very long distance. A tornado which affected Great Bend, Kansas in November, 1915 was an extreme case, where a "rain of debris" occurred 80 miles (130 km) from the town, a sack of flour was found 110 miles (177 km) away, and a cancelled check from the Great Bend bank was found in a field outside of Palmyra, Nebraska, 305 miles (491 km) to the northeast.[75] Waterspouts and tornadoes have been advanced as an explanation for instances of raining fish and other animals.[76]

Safety
Though tornadoes can strike in an instant, there are precautions and preventative measures that people can take to increase the chances of surviving a tornado. Authorities such as the Storm Prediction Center advise having a tornado plan. When a tornado warning is issued, going to a basement or an interior first-floor room of a sturdy building greatly increases chances of survival.[77] In tornado-prone areas, many buildings have storm cellars on the property. These underground refuges have saved thousands of lives.[78]

Some countries have meteorological agencies which distribute tornado forecasts and increase levels of alert of a possible tornado (such as tornado watches and warnings in the United States and Canada). Weather radios provide an alarm when a severe weather advisory is issued for the local area, though these are mainly available only in the United States.

Unless the tornado is far away and highly visible, meteorologists advise that drivers park their vehicles far to the side of the road (so as not to block emergency traffic), and find a sturdy shelter. If no sturdy shelter is nearby, getting low in a ditch is the next best option. Highway overpasses are extremely bad shelter during tornadoes (see next section).[79]

Myths and misconceptions

Salt Lake City Tornado, August 11, 1999. This tornado disproved several myths, including the idea that tornadoes cannot occur in areas like Utah.Main article: Tornado myths
It is often thought that opening windows will lessen the damage caused by the tornado. While there is a large drop in atmospheric pressure inside a strong tornado, it is unlikely that the pressure drop would be enough to cause the house to explode. Some research indicates that opening windows may actually increase the severity of the tornado's damage. A violent tornado can destroy a house whether its windows are open or closed.[80][81]

Another commonly held belief is that highway overpasses provide adequate shelter from tornadoes. On the contrary, a highway overpass is a dangerous place during a tornado. In the 1999 Oklahoma tornado outbreak of May 3, 1999, three highway overpasses were directly struck by tornadoes, and at all three locations there was a fatality, along with many life-threatening injuries. The small area under the overpasses is believed to cause a wind tunnel effect.[82] By comparison, during the same tornado outbreak, more than 2000 homes were completely destroyed, with another 7000 damaged, and yet only a few dozen people died in their homes.[79]

An old belief is that the southwest corner of a basement provides the most protection during a tornado. The safest place is the side or corner of an underground room opposite the tornado's direction of approach (usually the northeast corner), or the central-most room on the lowest floor. Taking shelter under a sturdy table, in a basement, or under a staircase increases chances of survival even more.[80][81]

Finally, there are areas which people believe to be protected from tornadoes, whether by a major river, a hill or mountain, or even protected by supernatural forces. Tornadoes have been known to cross major rivers, climb mountains,[83] and affect valleys. As a general rule, no area is "safe" from tornadoes, though some areas are more susceptible than others.[22][80][81] (See Tornado climatology).

Ongoing research

A Doppler On Wheels unit observing a tornado near Attica, KansasMeteorology is a relatively young science and the study of tornadoes even more so. Although researched for about 140 years and intensively for around 60 years, there are still aspects of tornadoes which remain a mystery.[84] Scientists have a fairly good understanding of the development of thunderstorms and mesocyclones, and the meteorological conditions conducive to their formation; however, the step from supercell (or other respective formative processes) to tornadogenesis and predicting tornadic vs. non-tornadic mesocyclones is not yet well known and is the focus of much research.

Also under study are the low-level mesocyclone and the stretching of low-level vorticity which tightens into a tornado, namely, what are the processes and what is the relationship of the environment and the convective storm. Intense tornadoes have been observed forming simultaneously with a mesocyclone aloft (rather than succeeding mesocyclogenesis) and some intense tornadoes have occurred without a mid-level mesocyclone. In particular, the role of downdrafts, particularly the rear-flank downdraft, and the role of baroclinic boundaries, are intense areas of study.

Reliably predicting tornado intensity and longevity remains a problem, as do details affecting characteristics of a tornado during its life cycle and tornadolysis. Other rich areas of research are tornadoes associated with mesovortices within linear thunderstorm structures and within tropical cyclones.[85]

Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued, especially in under-developed countries. Analysis of observations including both stationary and mobile (surface and aerial) in-situ and remote sensing (passive and active) instruments generates new ideas and refines existing notions. Numerical modeling also provides new insights as observations and new discoveries are integrated into our physical understanding and then tested in computer simulations which validate new notions as well as produce entirely new theoretical findings, many of which are otherwise unattainable. Importantly, development of new observation technologies and installation of finer spatial and temporal resolution observation networks have aided increased understanding and better predictions.

Research programs, including field projects such as VORTEX (Verification of the Origins of Rotation in Tornadoes Experiment), deployment of TOTO (the TOtable Tornado Observatory), Doppler On Wheels (DOW), and dozens of other programs, hope to solve many questions that still plague meteorologists.[40] Universities, government agencies such as the National Severe Storms Laboratory, private-sector meteorologists, and the National Center for Atmospheric Research are some of the organizations very active in research; with various sources of funding, both private and public, a chief entity being the National Science Foundation.

gobi Desert

2009-10-22T08:27:00.000-07:00

The Gobi (Mongolian: Говь, Govi, "semidesert"; Chinese: 戈壁(沙漠) Gēbì (Shāmò)) is the largest desert region in Asia. It covers parts of northern and northwestern China, and of southern Mongolia. The desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Hexi Corridor and Tibetan Plateau to the southwest, and by the North China Plain to the southeast. The Gobi is made up of several distinct ecological and geographic regions based on variations in climate and topography. This desert is the fifth largest in the world.

The Gobi is most notable in history as part of the great Mongol Empire, and as the location of several important cities along the Silk Road.

The Gobi is a rain shadow desert formed by the Himalaya range blocking rain-carrying clouds from reaching the Gobi.

Contents [hide]
1 Geography
2 Climate
2.1 Climate (as of 2009)
3 Conservation, ecology, economy
4 Desertification
5 Ecoregions of the Gobi
5.1 Eastern Gobi desert steppe
5.2 Alashan Plateau semi-desert
5.3 Dzungarian Basin semi-desert
6 European exploration up to 1911
7 See also
8 References
9 Further reading
10 External links

[edit] Geography
The Gobi measures over 1,610 km (1,000 mi) from southwest to northeast and 800 km (497 mi) from north to south. The desert is widest in the west, along the line joining the Lake Bosten and the Lop Nor (87°-89° east). It occupies an arc of land 1,295,000 km2 (500,002 sq mi)[1] in area, making it fifth largest in the world and Asia's largest. Much of the Gobi is not sandy but is covered with bare rock.

The Gobi has several different Chinese names, including 沙漠 (shāmò, actually a generic term for deserts in general) and 瀚海 (hànhǎi, endless sea). In its broadest definition, the Gobi includes the long stretch of desert and semi-desert area extending from the foot of the Pamirs, 77° east, to the Greater Khingan Mountains, 116°-118° east, on the border of Manchuria; and from the foothills of the Altay, Sayan, and Yablonoi mountain ranges on the north to the Kunlun Shan, Altun Shan, and Qilian shan ranges, which form the northern edges of the Tibetan Plateau, on the south.[citation needed]

A relatively large area on the east side of the Greater Khingan range, between the upper waters of the Songhua (Sungari) and the upper waters of the Liao-ho, is also reckoned to belong to the Gobi by conventional usage. On the other hand, geographers and ecologists prefer to regard the western area of the Gobi region (as defined above), the basin of the Tarim in Xinjiang and the desert basin of Lop Nor and Hami (Kumul) as forming a separate and independent desert, called the Taklamakan Desert.

The Nemegt Basin in the northwestern part of the Gobi Desert (in Mongolia) is famous for its fossil treasures, including early mammals, dinosaur eggs, and even prehistoric stone implements, some 100,000 years old.

[edit] Climate

Gobi by NASA World Wind
Sand dunes in Inner Mongolia, China
Bactrian camels by the sand dunes of Khongoryn Els, Gurvansaikhan NP, Mongolia
The sand dunes of Khongoryn Els, Gurvansaikhan NP, Mongolia
Legendary "olgoi khorkhoi" worm said to inhabit the Gobi in MongoliaThe Gobi is a cold desert, and it is not uncommon to see frost and occasionally snow on its dunes. Besides being quite far north, it is also located on a plateau roughly 910–1,520 meters (3,000–5,000 ft) above sea level, which further contributes to its low temperatures. An average of approximately 194 millimeters (7.6 in) of rain falls per year in the Gobi. Additional moisture reaches parts of the Gobi in winter as snow is blown by the wind from the Siberian Steppes. These winds cause the Gobi to reach extremes of temperature ranging from –40°C (-40°F) in winter to +50°C (122°F) in summer.[2]

[edit] Climate (as of 2009)
The climate of the Gobi is one of great extremes, combined with rapid changes of temperature, not only through the year but even within 24 hours (by as much as 35 °C or 61 °F).

Temperature Sivantse (1190 m) Ulaanbaatar (1150 m)
Annual mean -2.5 °C (27 °F) 2.8 °C (37 °F)
January mean -26.5 °C (-15.7 °F) -16.5 °C (2 °F)
July mean 17.5 °C (63.5 °F) 19.0 °C (66 °F)
Extremes 38.0 °C and -43 °C (100 °F and -45 °F) 33.9 °C and -47 °C (93 °F and -52 °F)

Even in southern Mongolia the thermometer goes down as low as -32.8 °C (-27 °F), and in Alxa it rises as high as 37 °C (98.6 °F) in July.

Average winter minimals are a frigid -40 °C (-40 °F) while summertime temperatures are warm to hot, highs range up to 50 °C (122 °F). Most of the precipitation falls during the summer.

Although the southeast monsoons reach the southeast parts of the Gobi, the area throughout this region is generally characterized by extreme dryness, especially during the winter. Hence, the icy sandstorms and snowstorms of spring and early summer plus early January (winter)

[edit] Conservation, ecology, economy
The Gobi Desert is the source of many important fossil finds, including the first dinosaur eggs.

These deserts and the surrounding regions sustain many animals, including black-tailed gazelles, marbled polecats, bactrian camels, Mongolian wild ass and sandplovers, and are occasionally visited by snow leopards, brown bears, and wolves. The desert features a number of drought-adapted shrubs such as gray sparrow's saltwort, gray sagebrush, and low grasses such as needle grass and bridlegrass.

The area is vulnerable to trampling by livestock and off-road vehicles (human impacts are greater in the eastern Gobi Desert, where rainfall is heavier and may sustain livestock). In Mongolia, grasslands have been degraded by goats, raised by nomadic herders as source of cashmere wool. Economic trends of livestock privatization and the collapse of the urban economy have caused people to return to rural lifestyles, a movement contrary to urbanization.

Large copper and gold deposits located at Oyuu Tolgoi, about 80 kilometers from the Chinese border into Mongolia, are being investigated for mining operations.[3]

[edit] Desertification
Currently, the Gobi desert is expanding at an alarming rate, in a process known as desertification. The expansion is particularly rapid on the southern edge into China, which has seen 3,600 km2 (1,390 sq mi) of grassland overtaken every year by the Gobi Desert. Dust storms, which used to occur regularly in China, have seen a dramatic increase in occurrence in the past 20 years, mainly due to desertification, and causing further damage to China's agriculture economy.

The expansion of the Gobi is attributed mostly to human activities, notably deforestation, overgrazing, and depletion of water resources. China has made various plans to try to slow the expansion of the desert, which have met with some small degree of success, but usually have no major impact. The most recent plan involves the planting of the Green Wall of China, a huge ring of newly-planted forests that the Chinese government hopes will act as a buffer against further expansion.

[edit] Ecoregions of the Gobi
The Gobi, broadly defined, can be divided into five distinct dry ecoregions.

The 'Eastern Gobi desert steppe' is the easternmost of the Gobi ecoregions, covering an area of 281,800 km2 (108,804 sq mi). It extends from the Inner Mongolian Plateau in China northward into Mongolia. It includes the Yin Mountains and many low-lying areas with salt pans and small ponds. It is bounded by the Mongolian-Manchurian grassland to the north, the Yellow River Plain to the southeast, and the Alashan Plateau semi-desert to the southeast and east.

The Alashan Plateau semi-desert lies west and southwest of the Eastern Gobi desert steppe. It consists of the desert basins and low mountains lying between the Gobi Altai range on the north, the Helan Mountains to the southeast, and the Qilian Mountains and northeastern portion of the Tibetan Plateau on the southwest.

The Gobi Lakes Valley desert steppe ecoregion lies north of Alashan Plateau semi-desert, between the Gobi Altai range to the south and the Khangai Mountains to the north.

The Dzungarian Basin semi-desert includes the desert basin lying between the Altai mountains on the north and the Tian Shan range on the south. It includes the northern portion of China's Xinjiang province and extends into the southeastern corner of Mongolia. The Alashan Plateau semi-desert lies to the east, and the Emin Valley steppe to the west, on the China-Kazakhstan border.

The Tian Shan range separates the Dzungarian Basin semi-desert from the Taklamakan Desert, which is a low, sandy desert basin surrounded by the high mountain ranges of the Tibetan Plateau to the south and the Pamirs to the west. The Taklamakan Desert ecoregion includes the Desert of Lop.

[edit] Eastern Gobi desert steppe
Here the surface is extremely diversified, although there are no great differences in vertical elevation. Between Ulaanbaatar (48°00′N 107°00′E / 48°N 107°E / 48; 107) and the little lake of Iren-dubasu-nor (43°45′N 111°50′E / 43.75°N 111.833°E / 43.75; 111.833 ) the surface is greatly eroded, and consists of broad flat depressions and basins separated by groups of flat-topped mountains of relatively low elevation 150 to 180 m (490 to 590 ft)), through which archaic rocks crop out as crags and isolated rugged masses. The floors of the depressions lie mostly between 900 to 1,000 m (3,000 to 3,300 ft) above sea-level. Farther south, between Iren-dutiasu-nor and the Hwang-ho comes a region of broad tablelands alternating with flat plains, the latter ranging at altitudes of 1000–1100 m and the former at 1,070 to 1,200 m (3,500 to 3,900 ft). The slopes of the plateaus are more or less steep, and are sometimes penetrated by "bays" of the lowlands. As the border-range of the Hyangan is approached, the country steadily rises up to 1,370 m (4,500 ft) and then to 1,630 m (5,300 ft). Here small lakes frequently fill the depressions, though the water in them is generally salt or brackish. Both here and for 320 km (199 mi) south of Ulaanbaatar, streams are frequent and grass grows more or less abundantly. There is, however, through all the central parts, until the bordering mountains are reached, an utter absence of trees and shrubs. Clay and sand are the predominant formations, the watercourses, especially in the north, being frequently excavated 2 to 3 m (6 ft 7 in to 9 ft 10 in) deep, and in many places in the flat, dry valleys or depressions farther south beds of loess, 5 to 6 m (16 to 20 ft) thick, are exposed. West of the route from Ulaanbaatar to Kalgan the country presents approximately the same general features, except that the mountains are not so irregularly scattered in groups but have more strongly defined strikes, mostly east to west, west-north-west to east-south-east, and west-south-west to east-north-east.

The altitudes too are higher, those of the lowlands ranging from 1,000 to 1,700 m (3,300 to 5,600 ft), and those of the ranges from 200 to 500 m (660 to 1,600 ft) higher, though in a few cases they reach altitudes of 2,400 m (7,900 ft). The elevations do not, however, form continuous chains, but make up a congeries of short ridges and groups rising from a common base and intersected by a labyrinth of ravines, gullies, glens and basins. But the tablelands, built up of the horizontal red deposits of the Han-gai (Obruchev's Gobi formation) which are characteristic of the southern parts of eastern Mongolia, are absent here or occur only in one locality, near the Shara-muren river, and are then greatly intersected by gullies or dry watercourses. Here there is, however, a great dearth of water, no streams, no lakes, no wells, arid precipitation falls but seldom. The prevailing winds blow from the west and northwest and the pall of dust overhangs the country as in the Takla Makan and the desert of Lop. Characteristic of the flora are wild garlic, Kalidium gracile, wormwood, saxaul, Nitraria schoberi, Caragana, Ephedra, saltwort and the grass Lasiagrostis splendens. The taana wild onion Allium polyrrhizum is the main browse eaten by many herd animals, and Mongolians claim that this is essential to produce the correct, slightly hazelnut-like flavour of camel airag (fermented milk).

This great desert country of Gobi is crossed by several trade routes, some of which have been in use for thousands of years. Among the most important are those from Kalgan (at the Great Wall) to Ulaanbaatar (960 km (597 mi)), from Jiuquan (in Gansu) to Hami 670 km (416 mi) from Hami to Beijing (2,000 km (1,243 mi)), from Hohhot to Hami and Barkul, and from Lanzhou (in Gansu) to Hami.

[edit] Alashan Plateau semi-desert
The southwestern portion of the Gobi, known also as the Hsi-tau and the Little Gobi, fills the space between the great north loop of the Yellow River on the east, the Ejin River on the west, and the Qilian Mountains and narrow rocky chain of Longshou , 3,200 to 3,500 m (10,000 to 11,000 ft) in altitude, on the southwest. The Ordos Desert, which covers the northeastern portion of the Ordos Plateau, in the great north loop of the Huang He, is part of this ecoregion. It belongs to the middle basin of the three great depressions into which Potanin divides the Gobi as a whole. "Topographically," says Przhevalsky, "it is a perfectly level plain, which in all probability once formed the bed of a huge lake or inland sea." The data upon which he bases this conclusion are the level area of the region as a whole, the hard saldgine clay and the sand-strewn surface, and lastly the salt lakes which occupy its lowest parts. For hundreds of kilometers there is nothing to be seen but bare sands; in some places they continue so far without a break that the Mongols call them Tengger (i.e. sky). These vast expanses are absolutely waterless, nor do any oases relieve the unbroken stretches of yellow sand which alternate with equally vast areas of saline clay or, nearer the foot of the mountains, with barren shingle. Although on the whole a level country with a general altitude of 1,000 to 1,500 m (3,300 to 4,900 ft), this section, like most other parts of the Gobi, is crowned by a chequered network of hills and broken ranges going up 300 m higher. The vegetation is confined to a few varieties of bushes and a dozen kinds of grasses and herbs, the most conspicuous being saxaul (Haloxylon ammondendron) and Agriophyllum gobicum. The others include prickly convolvulus, field wormwood (Artemisia campestris), acacia, Inula ammophila, Sophora flavescens, Convolvulus ammanii, Peganum and Astragalus, but all dwarfed, deformed and starved. The fauna consists of little else except antelopes, the wolf, fox, hare, hedgehog, marten, numerous lizards and a few birds, e.g. the sandgrouse, lark, stonechat, sparrow, crane, Henderson's Ground Jay (Podoces hendersoni), Horned Lark (Eremophila alpestris), and Crested Lark (Galerida cristata).

[edit] Dzungarian Basin semi-desert
The Yulduz valley or valley of the Haidag-gol (43°N 83°E / 43°N 83°E / 43; 83–43°N 86°E / 43°N 86°E / 43; 86) is a mini desert enclosed by two prominent members of the Shanashen Trahen Osh mountain range, namely the chucis and the kracenard pine rallies, running perpendicular and far from one another. As they proceed south they transcend and transpose, sweeping back on east and west, respectively so as to leave room for the Lake Bosten. These two ranges mark the northern and the southern edges respectively of a great swelling, which extends eastward for nearly twenty degrees of longitude. On its northern side the Chol-tagh descends steeply, and its foot is fringed by a string of deep depressions, ranging from Lukchun (130 m (427 ft) below sea level) to Hami (850 m (2,789 ft) above sea-level). To the south of the Kuruk-tagh lie the desert of Lop Nur, the Kum-tagh desert, and the valley of the Bulunzir-gol. To this great swelling, which arches up between the two border-ranges of the Chol-tagh and Kuruk-tagh, the Mongols give the name of Ghashuun-Gobi or Salt Desert. It is some 130 to 160 km (81 to 99 mi) across from north to south, and is traversed by a number of minor parallel ranges, ridges and chains of hills, and down its middle runs a broad stony valley, 40 to 80 km (25 to 50 mi) wide, at an elevation of 900 to 1,370 m (3,000 to 4,500 ft). The Chol-tagh, which reaches an average altitude of 1,800 m (5,900 ft), is absolutely sterile, and its northern foot rests upon a narrow belt of barren sand, which leads down to the depressions mentioned above.

The Kuruk-tagh is the greatly disintegrated, denuded and wasted relic of a mountain range which formerly was of incomparably greater magnitude. In the west, between Lake Bosten and the Tarim, it consists of two, possibly of three, principal ranges, which, although broken in continuity, run generally parallel to one another, and embrace between them numerous minor chains of heights. These minor ranges, together with the principal ranges, divide the region into a series of long; narrow valleys, mostly parallel to one another and to the enclosing mountain chains, which descend like terraced steps, on the one side towards the depression of Lukchun and on the other towards the desert of Lop. In many cases these latitudinal valleys are barred transversely by ridges or spurs, generally elevations en masse of the bottom of the valley. Where such elevations exist, there is generally found, on the east side of the transverse ridge, a cauldron-shaped depression, which some time or other has been the bottom of a former lake, but is now nearly a dry salt-basin. The surface configuration is in fact markedly similar to that which occurs in the inter-mount latitudinal valleys of the Kunlun Mountains. The hydrography of the Ghashiun-Gobi and the Kuruk-tagh is determined by these chequered arrangements of the latitudinal valleys. Most of the principal streams, instead of flowing straight down these valleys, cross them diagonally and only turn west after they have cut their way through one or more of the transverse barrier ranges. To the highest range on the great swelling Gruni-Grzhimailo gives the name of Tuge-tau, its altitude being 2,700 m (8,858 ft) above the level of the sea and some 1,200 m (3,937 ft) above the crown of the swelling itself. This range he considers to belong to the Choltagh system, whereas Sven Hedin would assign it to the Kuruk-tagh. This last, which is pretty certainly identical with the range of Kharateken-ula (also known as the Kyzyl-sanghir, Sinir, and Singher Mountains), that overlooks the southern shore of the Lake Bosten, though parted from it by the drift-sand desert of Ak-bel-kum (White Pass Sands), has at first a westnorthwest to eastsoutheast strike, but it gradually curves round like a scimitar towards the eastnortheast and at the same time gradually decreases in elevation. In 91° east, while the principal range of the Kuruk-tagh system wheels to the eastnortheast, four of its subsidiary ranges terminate, or rather die away somewhat suddenly, on the brink of a long narrow depression (in which Sven Hedin sees a northeast bay of the former great Central Asian lake of Lop-nor), having over against them the écheloned terminals of similar subordinate ranges of the Pe-shan (Boy-san) system (see below). The Kuruk-tagh is throughout a relatively low, but almost completely barren range, being entirely destitute of animal life, save for hares, antelopes and wild camels, which frequent its few small, widely scattered oases. The vegetation, which is confined to these same relatively favoured spots, is of the scantiest and is mainly confined to bushes of saxaul (Haloxylon), Anabasis, reeds (kamish), tamarisks, poplars, and Ephedra

[edit] European exploration up to 1911
The Gobi had a long history of human habitation, mostly by nomadic peoples. By the early 20th century the region was under the nominal control of Manchu-China, and inhabited mostly by Mongols, Uyghurs, and Kazakhs. The Gobi desert as a whole was only very imperfectly known to outsiders, information being confined to the observations which individual travellers had made from their respective itineraries across the desert. Amongst the European explorers who contributed to early 20th century understanding of the Gobi, the most important were:

Jean-François Gerbillon (1688–1698)
Eberhard Isbrand Ides (1692–1694)
Lorenz Lange (1727–1728 and 1736)
Fuss and Alexander G. von Bunge (1830–1831)
Hermann Fritsche (1868–1873)
Pavlinov and Z.L. Matusovski (1870)
Ney Elias (1872–1873)
Nikolai Przhevalsky (1870–1872 and 1876–1877)
Zosnovsky (1875)
Mikhail V. Pevtsov (1878)
Grigory Potanin (1877 and 1884–1886)
Count Béla Széchenyi and Lajos Lóczy (1879–1880)
The brothers G. E. Grumm-Grshimailo (1889–1890) and ? Grumm-Grshimailo.
Pyotr Kuzmich Kozlov (1893–1894 and 1899–1900)
Vsevolod I. Roborovsky (1894)
Vladimir Obruchev (1894–1896)
Karl Josef Futterer and Dr. Holderer (1896)
Charles-Etienne Bonin (1896 and 1899)
Sven Hedin (1897 and 1900–1901)
K. Bogdanovich (1898)
Ladyghin (1899–1900) and Katsnakov (1899–1900)

Equator

2009-10-22T08:24:00.000-07:00

The equator

The equator is the intersection of the Earth's surface with the plane perpendicular to the Earth's axis of rotation and containing the Earth's center of mass. In simpler language, it is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth into a Northern Hemisphere and a Southern Hemisphere. The equators of other planets and astronomical bodies are defined analogously.

Contents [hide]
1 Geodesy of the equator
2 Equatorial seasons and climate
3 Equatorial countries and territories
4 "Crossing the Line"
5 Exact length of the equator
6 See also
7 Notes
8 References
9 External links

[edit] Geodesy of the equator

Road sign marking the Equator near Nanyuki, KenyaThe latitude of the equator is 0°. The length of Earth's equator is about 40,075 kilometres (24,901.5 mi).

The equator is one of the five main circles of latitude that are based on the relationship between the Earth's axis of rotation and the plane of the Earth's orbit around the sun. It is the only line of latitude which is also a great circle. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the celestial equator.

The Sun in its seasonal movement through the sky, passes directly over the equator twice each year, on the March and September equinoxes. At the equator, the rays of the sun are perpendicular to the surface of the earth on these dates.

The equator marked as it crosses Ilhéu das Rolas, in São Tomé and PríncipePlaces on the equator experience the quickest rates of sunrise and sunset in the world. They are also the only places in the world where the sun can go directly from the zenith to the nadir and from the nadir to the zenith. Such places also have a theoretical constant 12 hours of day and night throughout the year (in practice there are variations of a few minutes due to the effects of atmospheric refraction and because sunrise and sunset are measured from the time the edge of the Sun's disc is on the horizon, rather than its centre). North or south of the equator day length increasingly varies with latitude and the seasons.

The Earth bulges slightly at the equator. It has an average diameter of 12,750 kilometres (7,922 mi), but at the equator the diameter is approximately 43 kilometres (27 mi) greater than the polar diameter.

A monument marking the equator at the city of Pontianak, IndonesiaLocations near the equator are good sites for spaceports, such as the Guiana Space Centre in Kourou, French Guiana, as they are already moving faster than any other point on the Earth due to the Earth's rotation, and the added velocity reduces the amount of fuel needed to launch spacecraft. Spacecraft launched in this manner must launch to the east to use this effect.

For high precision work, the equator is not quite as fixed as the above discussion implies. The true equatorial plane must always be perpendicular to the Earth's spin axis. Although this axis is relatively stable, its position wanders in approximately a 9 metres (30 ft) radius circular motion each year. Thus, the true equator moves slightly. This, however, is only important for detailed scientific studies. The effect is quite small, and the width of a line marking the equator on almost any map will be much wider than the error.

[edit] Equatorial seasons and climate

The "Marco Zero" in Macapá, Brasil.Near the equator there is little distinction between summer, winter, autumn or spring. Temperatures are high year round (permanent "summer"), with the exception of periods during the wet season and at higher altitudes. In many tropical regions people identify two seasons: wet and dry. However, most places close to the equator are wet throughout the year, and seasons can vary depending on a variety of factors including elevation and proximity to an ocean. The rainy and humid conditions mean that the equatorial climate is not the hottest in the world.

The surface of the Earth at the equator is mostly ocean. The highest point on the equator is 4,690 metres (15,387 ft), at 00°00′00″S, 77°59′31″W, on the south slopes of Volcán Cayambe (summit 5,790 metres (18,996 ft)) in Ecuador. This is a short distance above the snow line, and this point and its immediate vicinity form the only section of the equator where snow lies on the ground.

[edit] Equatorial countries and territories
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The equator traverses the land and/or territorial waters of 14 countries. Starting at the Prime Meridian and heading eastwards, the equator passes through:

Co-ordinates Country, territory or sea Notes
0°0′N 0°0′E / 0°N 0°E / 0; 0 (Prime Meridian) Atlantic Ocean Gulf of Guinea
0°0′N 6°31′E / 0°N 6.517°E / 0; 6.517 (São Tomé and Príncipe) São Tomé and Príncipe Ilhéu das Rolas
0°0′N 6°31′E / 0°N 6.517°E / 0; 6.517 (Atlantic Ocean) Atlantic Ocean Gulf of Guinea
0°0′N 9°21′E / 0°N 9.35°E / 0; 9.35 (Gabon) Gabon
0°0′N 13°56′E / 0°N 13.933°E / 0; 13.933 (Republic of the Congo) Republic of the Congo
0°0′N 17°46′E / 0°N 17.767°E / 0; 17.767 (Democratic Republic of the Congo) Democratic Republic of the Congo
0°0′N 29°43′E / 0°N 29.717°E / 0; 29.717 (Uganda) Uganda
0°0′N 13°22′E / 0°N 13.367°E / 0; 13.367 (Lake Victoria) Lake Victoria Passing through some islands of Uganda
0°0′N 34°0′E / 0°N 34°E / 0; 34 (Kenya) Kenya
0°0′N 41°0′E / 0°N 41°E / 0; 41 (Somalia) Somalia
0°0′N 42°53′E / 0°N 42.883°E / 0; 42.883 (Indian Ocean) Indian Ocean Passing between Gaafu Dhaalu and Gnaviyani atolls, Maldives
0°0′N 98°12′E / 0°N 98.2°E / 0; 98.2 (Indonesia) Indonesia The Batu Islands, Sumatra and the Lingga Islands
0°0′N 104°34′E / 0°N 104.567°E / 0; 104.567 (Karimata Strait) Karimata Strait
0°0′N 109°9′E / 0°N 109.15°E / 0; 109.15 (Indonesia) Indonesia Borneo
0°0′N 117°30′E / 0°N 117.5°E / 0; 117.5 (Makassar Strait) Makassar Strait
0°0′N 119°40′E / 0°N 119.667°E / 0; 119.667 (Indonesia) Indonesia Sulawesi
0°0′N 120°5′E / 0°N 120.083°E / 0; 120.083 (Gulf of Tomini) Gulf of Tomini
0°0′N 124°0′E / 0°N 124°E / 0; 124 (Molucca Sea) Molucca Sea
0°0′N 127°24′E / 0°N 127.4°E / 0; 127.4 (Indonesia) Indonesia Kayoa and Halmahera islands
0°0′N 127°53′E / 0°N 127.883°E / 0; 127.883 (Halmahera Sea) Halmahera Sea
0°0′N 129°20′E / 0°N 129.333°E / 0; 129.333 (Indonesia) Indonesia Gebe Island
0°0′N 129°21′E / 0°N 129.35°E / 0; 129.35 (Pacific Ocean) Pacific Ocean Passing just north of Waigeo island, Indonesia
Passing just south of Aranuka atoll, Kiribati
Passing just south of Baker Island, United States Minor Outlying Islands
0°0′N 91°35′W / 0°N 91.583°W / 0; -91.583 (Ecuador) Ecuador Isabela Island in the Galápagos Islands
0°0′N 91°13′W / 0°N 91.217°W / 0; -91.217 (Pacific Ocean) Pacific Ocean
0°0′N 80°6′W / 0°N 80.1°W / 0; -80.1 (Ecuador) Ecuador
0°0′N 75°32′W / 0°N 75.533°W / 0; -75.533 (Colombia) Colombia
0°0′N 70°3′W / 0°N 70.05°W / 0; -70.05 (Brazil) Brazil Including some islands in the mouth of the Amazon River
0°0′N 49°20′W / 0°N 49.333°W / 0; -49.333 (Atlantic Ocean) Atlantic Ocean

Despite its name, no part of Equatorial Guinea's territory lies on the equator. However, its island of Annobón is about 155 kilometres (100 mi) south of the equator, and the rest of the country lies to the north. The country that comes closest to the equator without actually touching it is Peru.

[edit] "Crossing the Line"
Main article: Line-crossing ceremony
The English-speaking seafaring tradition maintains that all sailors who cross the equator during a nautical voyage must undergo rites of passage and elaborate rituals initiating them into The Solemn Mysteries of the Ancient Order of the Deep. Those who have never "crossed the line" are derisively referred to as "pollywogs" or simply "slimy wogs". Upon entering the domain of His Royal Majesty, Neptunus Rex, all wogs are subject to various initiation rituals performed by those members of the crew who have made the journey before. Upon completion of the initiation ceremony, the wogs are then known as "trusty Shellbacks". If the crossing of the equator is done at the 180th meridian, the title of "Golden Shellback" is conferred, recognizing the simultaneous entry into the realm of the Golden Dragon. If the crossing occurs at the Greenwich or Prime Meridian, the sailor is considered to be an "Emerald Shellback".[1]

[edit] Exact length of the equator
The equator is modeled exactly in two widely used standards as a circle of radius an integer number of meters. In 1976 the IAU standardized this radius as 6,378,140 metres (20,925,656 ft), subsequently refined by the IUGG to 6,378,137 metres (20,925,646 ft) and adopted in WGS-84, though the yet more recent IAU-2000 has retained the old IAU-1976 value. In either case, the length of the equator is by definition exactly 2π times the given standard, which to the nearest millimeter is 40,075,016.686 metres (131,479,713.54 ft) in WGS-84 and 40,075,035.535 metres (131,479,775.38 ft) in IAU-1976 and IAU-2000.[2]

The geographical mile is defined as one arc minute of the equator, and therefore has different values depending on which standard equator is used, namely 1,855.3248 metres (6,087.024 ft) or 1,855.3257 metres (6,087.027 ft) for respectively WGS-84 and IAU-2000, a difference of nearly a millimeter.

The earth is standardly modeled as a sphere flattened about 0.336% along its axis. This results in the equator being about 0.16% longer than a meridian (as a great circle passing through the two poles). The IUGG standard meridian is to the nearest millimeter 40,007,862.917 metres (131,259,392.77 ft), one arc minute of which is 1,852.216 metres (6,076.82 ft), explaining the SI standardization of the nautical mile as 1,852 metres (6,076 ft), more than 3 metres (10 ft) short of the geographical mile

Amazon rain forest

2009-10-22T08:21:00.000-07:00

The Amazon rainforest

(Brazilian Portuguese: Floresta Amazônica or Amazônia; Spanish: Selva Amazónica or Amazonia), also known as Amazonia, or the Amazon jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America. This basin encompasses seven million square kilometers (1.7 billion acres), of which five and a half million square kilometers (1.4 billion acres) are covered by the rainforest. This region includes territory belonging to nine nations. The majority of the forest is contained within Brazil, with 60% of the rainforest, followed by Peru with 13%, and with minor amounts in Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname, and French Guiana. States or departments in four nations bear the name Amazonas after it. The Amazon represents over half of the planet's remaining rainforests, and it comprises the largest and most species-rich tract of tropical rainforest in the world.

The Amazon rainforest was short-listed in 2008 as a candidate to one of the New7Wonders of Nature by the New Seven Wonders of the World Foundation. As of February 2009 the Amazon was ranking first in Group E, the category for forests, national parks and nature reserves.[1]

Contents [hide]
1 Etymology
2 History
3 Biodiversity
4 Deforestation
5 Conservation and climate change
5.1 Remote sensing
5.2 Impact of Amazon drought
6 See also
7 Notes
8 References
9 External links

Etymology
The name Amazon is said to arise from a war which Francisco de Orellana had with a tribe of Tapuyas and other tribes from South America. The women of the tribe fought alongside the men, as was the custom among the entire tribe.[2] Orellana's descriptions may have been accurate, but a few historians speculate that Orellana could have been mistaking indigenous men wearing "grass skirts" for women.[citation needed] Orellana derived the name Amazonas from the ancient Amazons of Asia and Africa described by Herodotus and Diodorus in Greek legends.[2]

Another etymology for the word suggests that it came originally from a native word amazona (Spanish spelling) or amassona (Portuguese spelling), meaning "destroyer (of) boats", in reference to the destructive nature of the root system possessed by some riparian plants.

History

Earth during the EoceneThe rainforest likely formed during the Eocene era, following the evolutionary appearance of angiosperm plants. It appeared following a global reduction of tropical temperatures when the Atlantic Ocean had widened sufficiently to provide a warm, moist climate to the Amazon basin. The rain forest has been in existence for at least 55 million years, and most of the region remained free of savanna-type biomes during that time period.[3][4]

Following the Cretaceous–Tertiary extinction event, the extinction of the dinosaurs and the wetter climate may have allowed the tropical rainforest to spread out across the continent. From 65–34 Mya, the rainforest extended as far south as 45°. Climate fluctuations during the last 34 million years have allowed savanna regions to expand into the tropics. During the Oligocene, for example, the rainforest spanned a relatively narrow band that lay mostly above latitude 15°N. It expanded again during the Middle Miocene, then retracted to a mostly inland formation at the last glacial maximum.[5] However, the rainforest still managed to thrive during these glacial periods, allowing for the survival and evolution of a broad diversity of species.[6]

During the mid-Eocene, it is believed that the drainage basin of the Amazon was split along the middle of the continent by the Purus Arch. Water on the eastern side flowed toward the Atlantic, while to the west water flowed toward the Pacific across the Amazonas Basin. As the Andes Mountains rose, however, a large basin was created that enclosed a lake; now known as the Solimões Basin. Within the last 5–10 million years, this accumulating water broke through the Purus Arch, joining the easterly flow toward the Atlantic.[7][8]

There is evidence that there have been significant changes in Amazon rainforest vegetation over the last 21,000 years through the Last Glacial Maximum (LGM) and subsequent deglaciation. Analyses of sediment deposits from Amazon basin paleolakes and from the Amazon Fan indicate that rainfall in the basin during the LGM was lower than for the present, and this was almost certainly associated with reduced moist tropical vegetation cover in the basin.[9] There is debate, however, over how extensive this reduction was. Some scientists argue that the rainforest was reduced to small, isolated refugia separated by open forest and grassland;[10] other scientists argue that the rainforest remained largely intact but extended less far to the north, south, and east than is seen today.[11] This debate has proved difficult to resolve because the practical limitations of working in the rainforest mean that data sampling is biased away from the center of the Amazon basin, and both explanations are reasonably well supported by the available data.

Based on archaeological evidence from an excavation at Caverna da Pedra Pintada, human inhabitants first settled in the Amazon region at least 11,200 years ago.[12] Subsequent development led to late-prehistoric settlements along the periphery of the forest by 1250 CE, which induced alterations in the forest cover.[13] Biologists believe that a population density of 0.2 persons/km2 is the maximum that can be sustained in the rain forest through hunting. Hence, agriculture is needed to host a larger population.[14] The first European to travel the length of the Amazon River was Francisco de Orellana in 1542.[15]

Biodiversity

Deforestation in the Amazon Rainforest threatens many species of tree frogs, which are very sensitive to environmental changes (pictured: Giant leaf frog)
Scarlet Macaw, which is indigenous to the American tropics.Wet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than the wet forests in Africa and Asia.[16] As the largest tract of tropical rainforest in the Americas, the Amazonian rainforests have unparalleled biodiversity. One in ten known species in the world live in the Amazon Rainforest.[17] This constitutes the largest collection of living plants and animal species in the world.

The region is home to about 2.5 million insect species,[18] tens of thousands of plants, and some 2,000 birds and mammals. To date, at least 40,000 plant species, 3,000 fish, 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically classified in the region.[19] One in five of all the birds in the world live in the rainforests of the Amazon. Scientists have described between 96,660 and 128,843 invertebrate species in Brazil alone.[20]

The diversity of plant species is the highest on Earth with some experts estimating that one square kilometer may contain over 75,000 types of trees and 150,000 species of higher plants. One square kilometer of Amazon rainforest can contain about 90,790 tonnes of living plants. The average plant biomass is estimated at 356 ± 47 tonnes ha−1.[21] To date, an estimated 438,000 species of plants of economic and social interest have been registered in the region with many more remaining to be discovered or catalogued.[22]

The green leaf area of plants and trees in the rainforest varies by about 25% as a result of seasonal changes. Leaves expand during the dry season when sunlight is at a maximum, then undergo abscission in the cloudy wet season. These changes provide a balance of carbon between photosynthesis and respiration.[23]

The rainforest contains several species that can pose a hazard. Among the largest predatory creatures are the Black Caiman, Jaguar and Anaconda. In the river, electric eels can produce an electric shock that can stun or kill, while Piranha are known to bite and injure humans.[24] Various species of poison dart frogs secrete lipophilic alkaloid toxins through their flesh. There are also numerous parasites and disease vectors. Vampire bats dwell in the rainforest and can spread the rabies virus.[25] Malaria, yellow fever and Dengue fever can also be contracted in the Amazon region.

Deforestation
Main article: Deforestation of the Amazon Rainforest
Deforestation is the conversion of forested areas to non-forested areas. The main sources of deforestation in the Amazon are human settlement and development of the land.[26] Prior to the early 1960s, access to the forest's interior was highly restricted, and the forest remained basically intact.[27] Farms established during the 1960s was based on crop cultivation and the slash and burn method. However, the colonists were unable to manage their fields and the crops because of the loss of soil fertility and weed invasion.[28] The soils in the Amazon are productive for just a short period of time, so farmers are constantly moving to new areas and clearing more land.[28] These farming practices led to deforestation and caused extensive environmental damage.[29]

Between 1991 and 2000, the total area of forest lost in the Amazon rose from 415,000 to 587,000 km2, with most of the lost forest becoming pasture for cattle.[30] Seventy percent of formerly forested land in the Amazon, and 91% of land deforested since 1970, is used for livestock pasture.[31][32] In addition, Brazil is currently the second-largest global producer of soybeans after the United States. The needs of soy farmers have been used to validate many of the controversial transportation projects that are currently developing in the Amazon. The first two highways successfully opened up the rain forest and led to increased settlement and deforestation. The mean annual deforestation rate from 2000 to 2005 (22,392 km2 per year) was 18% higher than in the previous five years (19,018 km2 per year).[33] At the current rate, in two decades the Amazon Rainforest will be reduced by 40%.[34]

NASA satellite observation of deforestation in the Mato Grosso state of Brazil. The transformation from forest to farm is evident by the paler square shaped areas under development.

Fires and Deforestation in the state of Rondônia.

One consequence of forest clearing in the Amazon: thick smoke that hangs over the forest.

Conservation and climate change
See also: Gaviotas
Environmentalists are concerned about the loss of biodiversity which will result from destruction of the forest, and also about the release of the carbon contained within the vegetation, which could accelerate global warming. Amazonian evergreen forests account for about 10% of the world's terrestrial primary productivity and 10% of the carbon stores in ecosystems[35]—of the order of 1.1 × 1011 metric tonnes of carbon.[36] Amazonian forests are estimated to have accumulated 0.62 ± 0.37 tons of carbon per hectare per year between 1975 and 1996.[36]

One computer model of future climate change caused by greenhouse gas emissions shows that the Amazon rainforest could become unsustainable under conditions of severely reduced rainfall and increased temperatures, leading to an almost complete loss of rainforest cover in the basin by 2100.[37][38] However, simulations of Amazon basin climate change across many different models are not consistent in their estimation of any rainfall response, ranging from weak increases to strong decreases.[39] The result indicates that the rainforest could be threatened though the 21st century by climate change in addition to deforestation.

In 1989, environmentalist C.M. Peters and two colleagues stated there is economic as well as biological incentive to protecting the rainforest. One hectare in the Peruvian Amazon has been calculated to have a value of $6820 if intact forest is sustainably harvested for fruits, latex, and timber; $1000 if clear-cut for commercial timber (not sustainably harvested); or $148 if used as cattle pasture.[40]

As indigenous territories continue to be destroyed by deforestation and ecocide, such as in the Peruvian Amazon[41] indigenous peoples' rainforest communities continue to disappear, while others, like the Urarina continue to struggle to fight for their cultural survival and the fate of their forested territories. Meanwhile, the relationship between nonhuman primates in the subsistence and symbolism of indigenous lowland South American peoples has gained increased attention, as has ethno-biology and community-based conservation efforts.

From 2002 to 2006, the conserved land in the Amazon Rainforest has almost tripled and deforestation rates have dropped up to 60%. About 1,000,000 square kilometres (250,000,000 acres) have been put onto some sort of conservation, which adds up to a current amount of 1,730,000 square kilometres (430,000,000 acres).[42]

Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.

Aerosols over the Amazon each September for four burning seasons (2005 through 2008). The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.

Aerial roots of red mangrove on an Amazonian river.

Remote sensing

This image reveals how the forest and the atmosphere interact to create a uniform layer of “popcorn” clouds.The use of remotely sensed data is dramatically improving conservationists' knowledge of the Amazon Basin. Given the objectivity and lowered costs of satellite-based land cover analysis, it appears likely that remote sensing technology will be an integral part of assessing the extent and damage of deforestation in the basin.[43] Furthermore, remote sensing is the best and perhaps only possible way to study the Amazon on a large-scale.[44]

The use of remote sensing for the conservation of the Amazon is also being used by the indigenous tribes of the basin to protect their tribal lands from commercial interests. Using handheld GPS devices and programs like Google Earth, members of the Trio Tribe, who live in the rainforests of southern Suriname, map out their ancestral lands to help strengthen their territorial claims.[45] Currently, most tribes in the Amazon do not have clearly defined boundaries, which make their territories easy targets for commercial poaching of natural resources. Through the use of cheap mapping technology, the Trio Tribe hopes to protect its ancestral land.

In order to accurately map the biomass of the Amazon and subsequent carbon related emissions, the classification of tree growth stages within different parts of the forest is crucial. In 2006 Tatiana Kuplich organized the trees of the Amazon into four categories: (1) mature forest, (2) regenerating forest [less than three years], (3) regenerating forest [between three and five years of regrowth], and (4) regenerating forest [eleven to eighteen years of continued development].[46] The researcher used a combination of Synthetic aperture radar (SAR) and Thematic Mapper (TM) to accurately place the different portions of the Amazon into one of the four classifications.

Impact of Amazon drought
In 2005, parts of the Amazon basin experienced the worst drought in 100 years,[47] and there were indications that 2006 could have been a second successive year of drought.[48] A 23 July 2006 article in the UK newspaper The Independent reported Woods Hole Research Center results showing that the forest in its present form could survive only three years of drought.[49][50] Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a "tipping point" where it would irreversibly start to die. It concludes that the forest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate.

According to the World Wide Fund for Nature, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires

sahara desert

2009-10-22T08:18:00.000-07:00

Sahara desert

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For other uses, see Sahara (disambiguation).

A satellite image of the Sahara by NASA World Wind
Tadrart Acacus desert in western Libya, part of the Sahara.The Sahara (Arabic: الصحراء الكبرى‎, aṣ-ṣaḥrā´ al-kubra, "The Greatest Desert") is the world's largest hot desert. At over 9,000,000 square kilometres (3,500,000 sq mi), it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe. The desert stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel: a belt of semi-arid tropical savanna that comprises the northern region of central and western Sub-Saharan Africa.

The Sahara has an intermittent history that may go back as much as 3 million years.[1] Some of the sand dunes can reach 180 metres (600 ft) in height.[2] The name comes from the Arabic word for desert: (صَحراء), "ṣaḥrā´" ( صحراء (help·info); /sˤɑħrɑːʔ/).[3][4]

Contents [hide]
1 Overview
2 Geography
3 Climate history
4 Ecoregions
5 Fauna
6 History
6.1 Berbers
6.2 Egyptians
6.3 Nubians
6.4 Phoenicians
6.5 Greeks
6.6 Urban civilization
6.7 Trans-Saharan trade
6.8 European imperialism
6.9 Modern times
7 Peoples and languages
8 Countries in the Sahara
9 See also
10 References
11 Notes
12 External links

Overview

The top image shows the Safsaf Oasis on the surface of the Sahara. The bottom (using radar) is the rock layer underneath, revealing black channels cut by the meandering of an ancient river that once fed the oasis.The Sahara's boundaries are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean Sea on the north, the Red Sea and Egypt on the east, and the Sudan and the valley of the Niger River on the south. The Sahara is divided into western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains (a region of desert mountains and high plateaus), Ténéré desert and the Libyan desert (the most arid region). The highest peak in the Sahara is Emi Koussi (3,415 m/11,200 ft) in the Tibesti Mountains in northern Chad.

The Sahara divides the continent of Africa into North and Sub-Saharan Africa. The southern border of the Sahara is marked by a band of semiarid savanna called the Sahel; south of the Sahel lies the lusher Sudan and the Congo River Basin. Most of the Sahara consists of rocky hamada; ergs (large sand dunes) form only a minor part.

People lived on the edge of the desert thousands of years ago[5] since the last ice age. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles [6] survive, with half found in the Tassili n'Ajjer in southeast Algeria. Fossils of dinosaurs, including Afrovenator, Jobaria and Ouranosaurus, have also been found here. The modern Sahara, though, is not lush in vegetation, except in the Nile Valley, at a few oases, and in the northern highlands, where Mediterranean plants such as the olive tree are found to grow. The region has been this way since about 5000 years ago. Some 2.5 million people currently live in the Sahara, most of these in Egypt, Mauritania, Morocco and Algeria. Dominant ethnicities in the Sahara are various Berber groups including Tuareg tribes, various Arabised Berber groups such as the Hassaniya-speaking Maure (Moors, also known as Sahrawis), and various black African ethnicities including Tubu, Nubians, Zaghawa, Kanuri, Peul (Fulani), Hausa and Songhai. Important cities located in the Sahara include Nouakchott, the capital of Mauritania; Tamanrasset, Ouargla, Bechar, Hassi Messaoud, Ghardaia, El Oued, Algeria; Timbuktu, Mali; Agadez, Niger; Ghat, Libya; and Faya-Largeau, Chad.

Geography

A geographical map of Africa, showing the ecological break that defines the Saharan areaThe Sahara covers huge parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia. It is one of three distinct physiographic provinces of the African massive physiographic division.

The desert landforms of the Sahara are shaped by wind (eolian) or by occasional rains, and include sand dunes and dune fields or sand seas (erg), stone plateaus (hamada), gravel plains (reg), dry valleys (wadi), and salt flats (shatt or chott).[7] Unusual landforms include the Richat Structure in Mauritania.

Several deeply dissected mountains and mountain ranges, many volcanic, rise from the desert, including the Aïr Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and the Red Sea hills. The highest peak in the Sahara is Emi Koussi, a shield volcano in the Tibesti range of northern Chad.

Most of the rivers and streams in the Sahara are seasonal or intermittent, the chief exception being the Nile River, which crosses the desert from its origins in central Africa to empty into the Mediterranean. Underground aquifers sometimes reach the surface, forming oases, including the Bahariya, Ghardaïa, Timimoun, Kufrah, and Siwah.

The central part of the Sahara is hyper-arid, with little vegetation. The northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis where moisture collects.

To the north, the Sahara reaches to the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Magreb, the Sahara borders Mediterranean forest, woodland, and scrub ecoregions of northern Africa, which have a Mediterranean climate characterized by a winter rainy season. According to the botanical criteria of Frank White[8] and geographer Robert Capot-Rey,[9][10] the northern limit of the Sahara corresponds to the northern limit of Date Palm cultivation (Phoenix dactylifera), and the southern limit of Esparto (Stipa tenacissima), a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the 100 mm (3.9 in) isohyet of annual precipitation.[11]

To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel.[9][10] According to climatic criteria, the southern limit of the Sahara corresponds to the 150 mm (5.9 in) isohyet of annual precipitation (note that this is a long-term average, since precipitation varies strongly from one year to another).[11]

Climate history

An oasis in the Ahaggar Mountains
An intense Saharan dust storm sent a massive dust plume northwestward over the Atlantic Ocean on March 2, 2003The climate of the Sahara has undergone enormous variation between wet and dry over the last few hundred thousand years.[12] During the last glacial period, the Sahara was even bigger than it is today, extending south beyond its current boundaries.[13] The end of the glacial period brought more rain to the Sahara, from about 8000 BC to 6000 BC, perhaps due to low pressure areas over the collapsing ice sheets to the north.[14]

Once the ice sheets were gone, northern Sahara dried out. But in southern Sahara, the drying trend was soon counteracted by the monsoon, which brought rain further north than it does today. The monsoon is due to heating of air over the land during summer. The hot air rises and pulls in cool, wet air from the ocean, which causes rain. Thus, though it seems counterintuitive, the Sahara was wetter when it received more solar insolation in the summer. This was caused by a stronger tilt in Earth's axis of orbit than today, and perihelion occurred at the end of July.[15]

By around 3400 BC, the monsoon retreated south to approximately where it is today,[16] leading to the gradual desertification of the Sahara.[17] The Sahara is now as dry as it was about 13,000 years ago.[12] These conditions are responsible for what has been called the Sahara pump theory.

The Sahara has one of the harshest climates in the world. The prevailing north-easterly wind often causes the sand to form sand storms and dust devils.[18] Half of the Sahara receives less than 2 centimetres (0.79 in) of rain per year, and the rest receives up to 10 cm (3.9 in) per year.[19] The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods, which can last for years.

The southern boundary of the Sahara, as measured by rainfall, was observed to both advance and retreat between 1980 and 1990. As a result of drought in the Sahel, the southern boundary moved south 130 kilometres (81 mi) overall during that period.[20]. Deforestation has also caused the Sahara to advance south in recent years[citation needed], as trees and bushes continue to be used as fuel source.

Recent signals indicate that the Sahara and surrounding regions are greening due to increased rainfall. Satellites show extensive regreening of the Sahel between 1982 and 2002, and in both Eastern and Western Sahara a more than 20 year long trend of increased grazing areas and flourishing trees and shrubs has been observed by climate scientist Stefan Kröpelin.[21]

Ecoregions

The major topographic features of the Saharan region.The Sahara comprises several distinct ecoregions, whose variations in temperature, rainfall, elevation, and soils harbor distinct communities of plants and animals. According to the World Wide Fund for Nature (WWF), the ecoregions of the Sahara include:

Atlantic coastal desert: The coastal desert occupies a narrow strip along the Atlantic coast, where fog generated offshore by the cool Canary Current provides sufficient moisture to sustain a variety of lichens, succulents, and shrubs. It covers 39,900 square kilometers (15,400 square miles) in Western Sahara and Mauritania.[22]
North Saharan steppe and woodlands: This ecoregion lies along the northern edge of the desert, next to the Mediterranean forests, woodlands, and scrub ecoregions of the northern Maghreb and Cyrenaica. Winter rains sustain shrublands and dry woodlands that form a transition between the Mediterranean climate regions to the north and the hyper-arid Sahara proper to the south. It covers 1,675,300 square km (646,800 square miles) in Algeria, Egypt, Libya, Mauritania, Morocco, Tunisia, and Western Sahara.[23]
Sahara desert: This ecoregion covers the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Vegetation is rare, and this ecoregion consists mostly of sand dunes (erg, chech, raoui), stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. It covers 4,639,900 square km (1,791,500 square miles) of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, and Sudan.[24]
South Saharan steppe and woodlands: The South Saharan steppe and woodlands occupy a narrow band running east and west between the hyper-arid Sahara and the Sahel savannas to the south. Movements of the equatorial Intertropical Convergence Zone (ITCZ) bring summer rains during July and August which average 100 to 200 mm (3.9 to 7.9 in), but vary greatly from year to year. These rains sustain summer pastures of grasses and herbs, with dry woodlands and shrublands along seasonal watercourses. The ecoregion covers 1,101,700 square km (425,400 square miles) in Algeria, Chad, Mali, Mauritania, and Sudan.[25]
West Saharan montane xeric woodlands: Several volcanic highlands in the western portion of the Sahara provide a cooler, moister environment that supports Saharo-Mediterranean woodlands and shrublands. The ecoregion covers 258,100 square kilometers (99,700 square miles), mostly in the Tassili n'Ajjer of Algeria, with smaller enclaves in the Aïr of Niger, the Dhar Adrar of Mauritania, and the Adrar des Iforas of Mali and Algeria.[26]
Tibesti-Jebel Uweinat montane xeric woodlands: The Tibesti and Jebel Uweinat highlands foster higher, more regular rainfall and cooler temperatures, which support woodlands and shrublands of palms, acacias, myrtle, oleander, Tamarix, and several rare and endemic plants. The ecoregion covers 82,200 square km (31,700 square miles) in the Tibesti of Chad and Libya, and Jebel Uweinat on the border of Egypt, Libya, and Sudan.[27]
Saharan halophytics: Seasonally-flooded saline depressions in the Sahara are home to halophytic, or salt-adapted, plant communities. The Saharan halophytics cover 54,000 square km (20,800 square miles), including the Qattara and Siwa depressions in northern Egypt, the Tunisian salt lakes of central Tunisia, Chott Melghir in Algeria, and smaller areas of Algeria, Mauritania, and Western Sahara.[28].
Tanezrouft: One of the harshest regions on Earth and the driest in the Sahara, contains no vegetation and very little life.
Fauna

Shadows of camels with travelers on dunes in TunisiaDromedary camels and goats are the most domesticated animals found in the Sahara. Because of its qualities of sobriety, endurance and speed, the dromedary is the favorite animal used by nomads.
The Leiurus quinquestriatus (aka deathstalker) scorpion which can be 10 cm (3.9 in) long. Its venom contains large amounts of agitoxin and scyllatoxin and is very dangerous; however, a sting from this scorpion rarely kills a healthy adult.
The monitor lizard. It has been suggested that the occasional habit of varanids to stand on their two hind legs and to appear to "monitor" their surroundings led to the original Arabic name waral ورل, which is translated to English as "monitor".[29]
Sand vipers, which average less than 50 cm (20 in) in length. Many have a pair of horns, one over each eye. Active at night, they usually lie buried in the sand with only their eyes visible. Bites are painful, but rarely fatal.
The African Wild Dog has some populations confirmed in the southern Sahara and is frequently misidentified as the cryptid Adjule.
The fennec fox, pale fox and rüppell's fox, are omnivorous canids living in many parts of Sahara.
The hyrax. It first appears in the fossil record over 40 million years ago, and for many millions of years hyraxes were the primary terrestrial herbivore in Africa.
The ostrich which is a flightless bird native to Africa. They have become rare.
The addax, a large white antelope, is a threatened species. Adapted to the desert, they can remain months without drinking, even a whole year.
The Saharan cheetah lives in Algeria, Togo, Niger, Mali, Benin, and Burkina Faso. There remain less than 250 mature cheetahs which are very cautious, fleeing any human presence. The cheetah avoids the sun from April to October. It then seeks the shelter of shrubs such as balanites and acacias. They are unusually pale.[30][31]
The dorcas gazelle is a north african gazelle that can also go for a long time without water.
There exist other animals in the Sahara (birds in particular) such as African Silverbill and Black-throated Firefinch among others.

History

Photo of the Sahara from 1908Berbers
Berbers are one of the oldest known inhabitants of the Sahara Desert.[citation needed] They are the people that occupied (and still occupy) more than two thirds of the Sahara's total surface.[citation needed]The Garamantes Berbers built a prosperous empire in the heart of the desert.[citation needed] The Tuareg nomads continue, to present day, to inhabit and move across wide Sahara surfaces in Algeria, Mali, Niger, Mauritania, and Libya. Some of the oldest Berber Tifinagh inscriptions are found in Southern Algeria, Northern Mali and Niger.[citation needed]

Egyptians
By 6000 BC predynastic Egyptians in the southwestern corner of Egypt were herding cattle and constructing large buildings. Subsistence in organized and permanent settlements in predynastic Egypt by the middle of the 6th millennium BC centered predominantly on cereal and animal agriculture: cattle, goats, pigs and sheep. Metal objects replaced prior ones of stone. Tanning of animal skins, pottery and weaving are commonplace in this era also.[32] There are indications of seasonal or only temporary occupation of the Al Fayyum in the 6th millennium BC, with food activities centering on fishing, hunting and food-gathering. Stone arrowheads, knives and scrapers are common.[33] Burial items include pottery, jewelry, farming and hunting equipment, and assorted foods including dried meat and fruit. Burial in desert environments appears to enhance Egyptian preservation rites, and dead are buried facing due west.[32] By 3400 BC, the Sahara was as dry as it is today, and it became a largely impenetrable barrier to humans, with only scattered settlements around the oases, but little trade or commerce through the desert. The one major exception was the Nile Valley. The Nile, however, was impassable at several cataracts, making trade and contact by boat difficult.

Nubians
During the Neolithic, before the onset of desertification, the central Sudan had been a rich environment supporting a large population ranging across what is now barren desert, like the Wadi el-Qa'ab. By the 5th millennium BC, the peoples who inhabited what is now called Nubia, were full participants in the "agricultural revolution," living a settled lifestyle with domesticated plants and animals. Saharan rock art of cattle and herdsmen found suggests the presence of a cattle cult like those found in Sudan and other pastoral societies in Africa today.[34] Megaliths found at Nabta Playa are overt examples of probably the world's first known Archaeoastronomy devices, predating Stonehenge by some 1000 years.[35] This complexity, as observed at Nabta Playa, and as expressed by different levels of authority within the society there, likely formed the basis for the structure of both the Neolithic society at Nabta and the Old Kingdom of Egypt.[36]

Phoenicians

A Saharan village in MaliThe peoples of Phoenicia, who flourished between 1200-800 BC, created a confederation of kingdoms across the entire Sahara to Egypt. They generally settled along the Mediterranean coast, as well as the Sahara, among the peoples of Ancient Libya, who were the ancestors of peoples who speak Berber languages in North Africa and the Sahara today, including the Tuareg of the central Sahara.

The Phoenician alphabet seems to have been adopted by the ancient Libyans of north Africa, and Tifinagh is still used today by Berber-speaking Tuareg camel herders of the central Sahara.

Sometime between 633 BC and 530 BC, Hanno the Navigator either established or reinforced Phoenician colonies in Western Sahara, but all ancient remains have vanished with virtually no trace. (See History of Western Sahara.)

Greeks
By 500 BC, a new influence arrived in the form of the Greeks. Greek traders spread along the eastern coast of the desert, establishing trading colonies along the Red Sea coast. The Carthaginians explored the Atlantic coast of the desert. But the turbulence of the waters and the lack of markets never led to an extensive presence further south than modern Morocco. Centralized states thus surrounded the desert on the north and east; it remained outside the control of these states. Raids from the nomadic Berber people of the desert were a constant concern of those living on the edge of the desert.

An Algerian man in urban dressUrban civilization
An urban civilization, the Garamantes, arose around this time in the heart of the Sahara, in a valley that is now called the Wadi al-Ajal in Fazzan, Libya.[12] The Garamantes achieved this development by digging tunnels far into the mountains flanking the valley to tap fossil water and bring it to their fields. The Garamantes grew populous and strong, conquering their neighbors and capturing many slaves (which were put to work extending the tunnels). The ancient Greeks and the Romans knew of the Garamantes and regarded them as uncivilized nomads. However, they traded with the Garamantes, and a Roman bath has been found in the Garamantes capital of Garama. Archaeologists have found eight major towns and many other important settlements in the Garamantes territory. The Garamantes civilization eventually collapsed after they had depleted available water in the aquifers, and could no longer sustain the effort to extend the tunnels still further into the mountains.[37]

Trans-Saharan trade
Main article: Trans-Saharan trade

The 12th Century traveller Benjamin of Tudela in the Sahara (Dumouza, 19th Century engraving)Following the Islamic conquest of North Africa in the seventh century CE, trade across the desert intensified. The kingdoms of the Sahel, especially the Ghana Empire and the later Mali Empire, grew rich and powerful exporting gold and salt to North Africa. The emirates along the Mediterranean Sea sent south manufactured goods and horses. From the Sahara itself, salt was exported. This process turned the scattered oasis communities into trading centres, and brought them under the control of the empires on the edge of the desert. A significant slave trade crossed the desert (See Arab slave trade).

This trade persisted for several centuries until the development in Europe of the caravel allowed ships, first from Portugal but soon from all Western Europe, to sail around the desert and gather the resources from the source in Guinea. The Sahara was rapidly remarginalized.

European imperialism
At the beginning of the 19th century, most of the northern Sahara, including most of present-day Algeria, Tunisia, Libya, and Egypt, was part of the Ottoman Empire. The Sahel and southern Sahara were home to several independent states.

European colonialism in the Sahara began in the 19th century. France conquered Algeria from the Ottomans in 1830, and French rule spread south from Algeria and eastwards from Senegal into the upper Niger to include present-day Algeria, Chad, Mali, Mauritania, Morocco (1912), Niger, and Tunisia (1881).

Egypt, under Muhammad Ali and his successors, conquered Nubia (1820-22), founded Khartoum (1823), and conquered Darfur (1874). Egypt, including the Sudan, became a British protectorate in 1882. Egypt and Britain lost control of the Sudan from 1882 to 1898 as a result of the Mahdist War. After its capture by British troops in 1898, the Sudan became a Anglo-Egyptian condominium.

Spain captured present-day Western Sahara after 1874. In 1912, Italy captured Libya from the Ottomans.

To promote the Roman Catholic religion in the desert, the Pope in 1868 appointed a delegate Apostolic of the Sahara and the Sudan; later in the 19th century his jurisdiction was reorganized into the Vicariate Apostolic of Sahara.

Modern times

A natural rock arch in south western LibyaEgypt became independent of Britain in 1936, although the Anglo-Egyptian Treaty of 1936 allowed Britain to keep troops in Egypt and maintained the British-Egyptian condominium in the Sudan. British military forces were withdrawn in 1954.

Most of the Saharan states achieved independence after World War II: Libya in 1951, Morocco, Sudan, and Tunisia in 1956, Chad, Mali, Mauritania, and Niger in 1960, and Algeria in 1962. Spain withdrew from Western Sahara in 1975, and it was partitioned between Mauritania and Morocco. Mauritania withdrew in 1979, but Morocco continues to hold the territory.

The modern era has seen a number of mines and communities develop to exploit the desert's natural resources. These include large deposits of oil and natural gas in Algeria and Libya and large deposits of phosphates in Morocco and Western Sahara.

A number of Trans-African highways have been proposed across the Sahara, including the Cairo-Dakar Highway along the Atlantic coast, the Trans-Sahara Highway from Algiers on the Mediterranean to Kano in Nigeria, the Tripoli-Cape Town Highway from Tripoli in Libya to Ndjamena in Chad, and the Cairo-Cape Town Highway which follows the Nile. Each of these highways is partially complete, with significant gaps and unpaved sections.

Peoples and languages
The Sahara is home to a number of peoples and languages. Arabic is the most widely spoken language in the Sahara, from the Atlantic to the Red Sea. Berber people are found from western Egypt to Morocco, including the Tuareg pastoralists of the central Sahara. The Beja live in the Red Sea Hills of southeastern Egypt and eastern Sudan. The Arabic, Berber, and Beja languages are part of the Afro-Asiatic language family.

Speakers of the Nilo-Saharan language family also inhabit the Sahara, including the Fur of Darfur in western Sudan and the Saharan languages of Niger, Chad and western Sudan, which includes the Kanuri, Tedaga, and Dazaga

Under ground water And surface water

2009-10-22T08:13:00.000-07:00

Groundwater

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Shipot, a common source of drinking water in a Ukrainian village.Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

Typically, groundwater is thought of as liquid water flowing through shallow aquifers, but technically it can also include soil moisture, permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of the Earth's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to the Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of Jupiter's moon Europa.

Image of the entire surface water flow of the Alapaha River near Jennings, Florida going into a sinkhole leading to the Floridan Aquifer groundwater.Contents [hide]
1 Aquifers
2 Water cycle
3 Issues
3.1 Overview
3.2 Overdraft
3.3 Subsidence
3.4 Seawater intrusion
3.5 Mining
3.6 Pollution
4 References
5 See also
6 External links

[edit] Aquifers

Groundwater withdrawal rates from the Ogallala Aquifer in the central U.S.Main article: Aquifer
An aquifer is a layer of porous substrate that contains and transmits groundwater. When water can flow directly between the surface and the saturated zone of an aquifer, the aquifer is unconfined. The deeper parts of unconfined aquifers are usually more saturated since gravity causes water to flow downward.

The upper level of this saturated layer of an unconfined aquifer is called the water table or phreatic surface. Below the water table, where generally all pore spaces are saturated with water is the phreatic zone.

Substrate with low porosity that permits limited transmission of groundwater is known as an aquitard. An aquiclude is a substrate with porosity that is so low it is virtually impermeable to groundwater.

A confined aquifer is an aquifer that is overlain by a relatively impermeable layer of rock or substrate such as an aquiclude or aquitard. If a confined aquifer follows a downward grade from its recharge zone, groundwater can become pressurized as it flows. This can create artesian wells that flow freely without the need of a pump and rise to a higher elevation than the static water table at the above, unconfined, aquifer.

The characteristics of aquifers vary with the geology and structure of the substrate and topography in which they occur. Generally, the more productive aquifers occur in sedimentary geologic formations. By comparison, weathered and fractured crystalline rocks yield smaller quantities of groundwater in many environments. Unconsolidated to poorly cemented alluvial materials that have accumulated as valley-filling sediments in major river valleys and geologically subsiding structural basins are included among the most productive sources of groundwater.

The high specific heat capacity of water and the insulating effect of soil and rock can mitigate the effects of climate and maintain groundwater at a relatively steady temperature. In some places where groundwater temperatures are maintained by this effect at about 50°F/10°C, groundwater can be used for controlling the temperature inside structures at the surface. For example, during hot weather relatively cool groundwater can be pumped through radiators in a home and then returned to the ground in another well. During cold seasons, because it is relatively warm, the water can be used in the same way as a source of heat for heat pumps that is much more efficient than using air. The relatively constant temperature of groundwater can also be used for heat pumps.

[edit] Water cycle

Relative groundwater travel times.Groundwater makes up about twenty percent of the world's fresh water supply, which is about 0.61% of the entire world's water, including oceans and permanent ice. Global groundwater storage is roughly equal to the total amount of freshwater stored in the snow and ice pack, including the north and south poles. This makes it an important resource which can act as a natural storage that can buffer against shortages of surface water, as in during times of drought.[1]

Groundwater is naturally replenished by surface water from precipitation, streams, and rivers when this recharge reaches the water table.[citation needed]

Groundwater can be a long-term 'reservoir' of the natural water cycle (with residence times from days to millennia), as opposed to short-term water reservoirs like the atmosphere and fresh surface water (which have residence times from minutes to years). The figure shows how deep groundwater (which is quite distant from the surface recharge) can take a very long time to complete its natural cycle.

The Great Artesian Basin in central and eastern Australia is one of the largest confined aquifer systems in the world, extending for almost 2 million km2. By analysing the trace elements in water sourced from deep underground, hydrogeologists have been able to determine that water extracted from these aquifers can be more than 1 million years old.

By comparing the age of groundwater obtained from different parts of the Great Artesian Basin, hydrogeologists have found it increases in age across the basin. Where water recharges the aquifers along the Eastern Divide, ages are young. As groundwater flows westward across the continent, it increases in age, with the oldest groundwater occurring in the western parts. This means that in order to have travelled almost 1000 km from the source of recharge in 1 million years, the groundwater flowing through the Great Artesian Basin travels at an average rate of about 1 metre per year.

[edit] Issues
[edit] Overview
Certain problems have beset the use of groundwater around the world. Just as river waters have been over-used and polluted in many parts of the world, so too have aquifers. The big difference is that aquifers are out of sight. The other major problem is that water management agencies, when calculating the ‘sustainable yield’ of aquifer and river water, have often counted the same water twice, once in the aquifer, and once in its connected river. This problem, although understood for centuries, has persisted, partly through inertia within government agencies. In Australia, for example, prior to the statutory reforms initiated by the Council of Australian Governments water reform framework in the 1990s, many Australian States managed groundwater and surface water through separate government agencies, an approach beset by rivalry and poor communication.

The time lags inherent in the dynamic response of groundwater to development have generally been ignored by water management agencies, decades after scientific understanding of the issue was consolidated. In brief, the effects of groundwater overdraft (although undeniably real) may take decades or centuries to manifest themselves. In a classic study in 1982, Bredehoeft and colleagues[2] modelled a situation where groundwater extraction in an intermontane basin withdrew the entire annual recharge, leaving ‘nothing’ for the natural groundwater-dependent vegetation community. Even when the borefield was situated close to the vegetation, 30% of the original vegetation demand could still be met by the lag inherent in the system after 100 years. By year 500 this had reduced to 0%, signalling complete death of the groundwater-dependent vegetation. The science has been available to make these calculations for decades; however water management agencies have generally ignored effects which will appear outside the rough timeframe of political elections (3 to 5 years). Sophocleous[2] argued strongly that management agencies must define and use appropriate timeframes in groundwater planning. This will mean calculating groundwater withdrawal permits based on predicted effects decades, sometimes centuries in the future.

As water moves through the landscape it collects soluble salts, mainly sodium chloride. Where such water enters the atmosphere through evapotranspiration, these salts are left behind. In irrigation districts, poor drainage of soils and surface aquifers can result in water tables coming to the surface in low-lying areas. Major land degradation problems of salinity and waterlogging result, combined with increasing levels of salt in surface waters. As a consequence, major damage has occurred to local economies and environments.[3]

Four important effects are worthy of brief mention. First, flood mitigation schemes, intended to protect infrastructure built on floodplains, have had the unintended consequence of reducing aquifer recharge associated with natural flooding. Second, prolonged depletion of groundwater in extensive aquifers can result in land subsidence, with associated infrastructure damage – as well as (thirdly) saline intrusion.[4] Fourth, draining acid sulphate soils, often found in low-lying coastal plains, can result in acidification and pollution of formerly freshwater and estuarine streams.[5]

Another cause for concern is that groundwater drawdown from over-allocated aquifers has the potential to cause severe damage to both terrestrial and aquatic ecosystems – in some cases very conspicuously but in others quite imperceptibly because of the extended period over which the damage occurs.[6]

[edit] Overdraft
Groundwater is a highly useful and often abundant resource. However, over-use, or overdraft, can cause major problems to human users and to the environment. The most evident problem (as far as human groundwater use is concerned) is a lowering of the water table beyond the reach of existing wells. Wells must consequently be deepened to reach the groundwater; in some places (e.g., California, Texas and India) the water table has dropped hundreds of feet because of excessive well pumping. In the Punjab region of India, for example, groundwater levels have dropped 10 meters since 1979, and the rate of depletion is accelerating.[7] A lowered water table may, in turn, cause other problems such as subsidence and saltwater intrusion.

Groundwater is also ecologically important. The importance of groundwater to ecosystems is often overlooked, even by freshwater biologists and ecologists. Groundwaters sustain rivers, wetlands and lakes, as well as subterranean ecosystems within karst or alluvial aquifers.

Not all ecosystems need groundwater, of course. Some terrestrial ecosystems - for example, those of the open deserts and similar arid environments - exist on irregular rainfall and the moisture it delivers to the soil, supplemented by moisture in the air. While there are other terrestrial ecosystems in more hospitable environments where groundwater plays no central role, groundwater is in fact fundamental to many of the world’s major ecosystems. Water flows between groundwaters and surface waters. Most rivers, lakes and wetlands are fed by, and (at other places or times) feed groundwater, to varying degrees. Groundwater feeds soil moisture through percolation, and many terrestrial vegetation communities depend directly on either groundwater or the percolated soil moisture above the aquifer for at least part of each year. Hypoheic zones (the mixing zone of streamwater and groundwater) and riparian zones are examples of ecotones largely or totally dependent on groundwater.

When we extract groundwater linked to a river system, we extract water from that river, even if the result is not evident for some time. And of course vice versa. Water management agencies around the world are still struggling to come to terms with this simple fact.

[edit] Subsidence
Main article: Groundwater-related subsidence
In its natural equilibrium state, the hydraulic pressure of groundwater in the pore spaces of the aquifer and the aquitard supports some of the weight of the overlying sediments. When groundwater is removed from aquifers by excessive pumping, pore pressures in the aquifer drop and compression of the aquifer may occur. This compression may be partially recoverable if pressures rebound, but much of it is not. When the aquifer gets compressed it may cause land subsidence, a drop in the ground surface. The city of New Orleans, Louisiana, is actually below sea level today, and its subsidence is partly caused by removal of groundwater from the various aquifer/aquitard systems beneath it. In the first half of the 20th century, the city of San Jose, California, dropped 13 feet from land subsidence caused by overpumping; this subsidence has been halted with improved groundwater management.

[edit] Seawater intrusion
Generally, in very humid or undeveloped regions, the shape of the water table mimics the slope of the surface. The recharge zone of an aquifer near the seacoast is likely to be inland, often at considerable distance. In these coastal areas, a lowered water table may induce sea water to reverse the flow toward the sea. Sea water moving inland is called a saltwater intrusion. Alternatively, salt from mineral beds may leach into the groundwater of its own accord.

[edit] Mining
Sometimes the water movement from the recharge zone to the place where it is withdrawn may take centuries (see figure above). When the usage of water is greater than the recharge, it is referred to as mining water (the water is often called fossil water because of its geologic age). Under those circumstances it is not a renewable resource.

[edit] Pollution

Iron oxide staining caused by reticulation from an unconfined aquifer in karst topography. Perth, Western Australia.Main article: Water pollution
Not all groundwater problems are caused by over-extraction. Pollutants released to the ground can work their way down into groundwater. Movement of water and dispersion within the aquifer spreads the pollutant over a wider area, which can then intersect with groundwater wells or find their way back into surface water, making the water supplies unsafe. The interaction of groundwater contamination with surface waters is analyzed by use of hydrology transport models.

The stratigraphy of the area plays an important role in the transport of these pollutants. An area can have layers of sandy soil, fractured bedrock, clay, or hardpan. Areas of karst topography on limestone bedrock are sometimes vulnerable to surface pollution from groundwater. Water table conditions are of great importance for drinking water supplies, agricultural irrigation, waste disposal (including nuclear waste), and other ecological issues.

Upon commercial real estate property transactions both groundwater and soil are the subjects of scrutiny, with a Phase I Environmental Site Assessment normally being prepared to investigate and disclose potential pollution issues.

Love Canal was one of the most widely known examples of groundwater pollution. In 1978, residents of the Love Canal neighborhood in upstate New York noticed high rates of cancer and an alarming number of birth defects. This was eventually traced to organic solvents and dioxins from an industrial landfill that the neighbourhood had been built over and around, which had then infiltrated into the water supply and evaporated in basements to further contaminate the air. Eight hundred families were reimbursed for their homes and moved, after extensive legal battles and media coverage.

Another example of widespread groundwater pollution is in the Ganges Plain of northern India and Bangladesh where severe contamination of groundwater by naturally occurring arsenic affects 25% of water wells in the shallower of two regional aquifers. The pollution occurs because aquifer sediments contain organic matter (dead plant material) that generates anaerobic (an environment without oxygen) conditions in the aquifer. These conditions result in the microbial dissolution of iron oxides in the sediment and thus the release of the arsenic, normally strongly bound to iron oxides, into the water. As a consequence, arsenic-rich groundwater is often iron-rich, although secondary processes often obscure the association of dissolved arsenic and dissolved iron.

Surface Water

Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water.

Surface water is naturally replenished by precipitation and naturally lost through discharge to evaporation and sub-surface seepage into the groundwater. Although there are other sources of groundwater, such as connate water and magmatic water, precipitation is the major one and groundwater originated in this way is called meteoric water.

Land surface water is the largest source of

Oceans Salinity

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Salinity

Mean sea-surface salinity. Grey shaded areas (land) exceed 36 psu (practical salinity units).
Click on image for full size (25K GIF)
Image courtesy of NOAA
About 70% of the Earth is covered with water, and we find 97% of that water in the oceans. Everyone who has taken in a mouthful of ocean water while swimming knows that the ocean is really salty.
All water has some dissolved material in it. This dissolved material can be solids, liquids or gases that have completely mixed with the water. This dissolved material which can come from the land, precipitation, or the atmosphere, is also referred to as dissolved salts. Dissolved salts are found in river water, groundwater, rain water, lake water, drinking water and so on. Yet, these are all considered fresh water. The difference between fresh water and ocean water is that ocean water contains many more dissolved salts.

Ocean water is about 3.5% salt. That means that if the oceans dried up completely, enough salt would be left behind to build a 180-mile-tall, one- mile-thick wall around the equator. And more than 90 percent of that salt would be sodium chloride, or ordinary table salt.

The oceans sure contain a lot of salt. How did that salt come to be there? It is thought that when the Earth was still young, many of the gases emitted from volcanoes dissolved in the primitive ocean, originally making it salty. Now, one of the main contributors of salt in the ocean is the continual rinsing of the Earth. Rivers, streams and groundwater all flow into the oceans. They carry water and dissolved minerals or salts from the rocks they have washed over. These dissolved salts then get deposited in the ocean. Another great contributor of salts to the ocean comes from the mid-ocean ridges, the areas of sea floor spreading. So, the oceans are getting saltier every day...but the rate of increase is so small we can't even measure it yet!

From the top of the ocean all the way to the depths of the ocean, salinity is between ~33-37 ppt or psu (average salinity of the ocean is 35 ppt). You can see from the image shown on this page that salinity for almost the entire ocean (at sea surface) is colored some shade of orange, corresponding to a salinity measurement around 33-36 ppt or psu. As shown on this graph, there are some geographic variations of salinity that are of interest. Salinity of the top layer of the ocean is closely linked with precipitation and evaporation. Evaporation leaves behind dissolved salts increasing salinity and precipitation "freshens" the top ocean layers. So, salinity is high in mid-latitudes where evaporation is high and precipitation is low (darker oranges). Salinity is low near the equator because precipitation is so high (lighter orange). Very high latitudes can also see decreases in salinity where sea ice melts and "freshens" the water (light orange and even yellow in the Arctic).

The oceans are naturally salty. The saline environment has quite an effect on life in the oceans. Most creatures that live in the ocean could not live in fresh water. However, when the highly saline waters of the ocean meet fresh water, an estuary is formed. This is a special environment where some creatures have learned to adapt to a mixture of fresh and salt water. When fresh water, ground water and soils are altered by human actions and salinity greatly increases, it can have an extreme detrimental effect on life there. Changes in salinity brought about by human residential, commercial and industrial activity can kill plant life, aquatic life, and animal life in a given area. Humans have the responsibility to make sure their actions are not causing this type of devastation. For more information on salinity and its effect on plants, soils and water, please use the links below...

More on salinity - measuring salinity, dissolved salts...

Salinity Versus Depth Profile for Ocean Water

The Oceans and Seas

Estuaries

A look at Chesapeake Bay

George E. Brown Jr. Salinity Laboratory - exploring soil-plant-water systems

The Salt Institute

Water Cycle

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Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water cycle, with these processes happening in the blink of an eye and over millions of years.

Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go in a hurry. The water in the apple you ate yesterday may have fallen as rain half-way around the world last year or could have been used 100 million years ago by Mama Dinosaur to give her baby a bath.

To explore the water cycle, choose a topic from the diagram or text links below.

Where do YOU think the water cycle begins? Give us your opinion.

A summary of the water cycle on a single Web page is also available:
Complete summary • Text only • Quick summary

Streamflow Surface runoff Freshwater storage
Ground-water discharge Ground-water storage Infiltration
Precipitation Snowmelt runoff to streams Springs
Water in the atmosphere Evaporation Evapotranspiration
Condensation Sublimation Ice and snow Oceans
Printing options: A print-friendly image of the diagram is available.

Teachers:

A version of the diagram without text | a diagram where you have to place the terms is available.
The National Oceanic and Atmospheric Administration (NOAA) has a water-cycle game that teachers can use to have their students get actively involved in simulating the journey water molecules may take as they travel within the water cycle.

Follow a drop through the water cycle.

A place mat showing the water cycle—great for kids.

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Water-cycle home Water Science home

Laboratory Rules

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SAFETY AND LABORATORY RULES

The scientific laboratory is a place of adventure and discovery. Some of the most important events in scientific history have happened in laboratories. The antibiotic powers of penicillin were discovered in a laboratory. The plastics used today for clothing and other products were first made in a laboratory. The list is endless.
One of the first things any scientist learns is that working in the laboratory can be an exciting experience. However, the laboratory can also be quite dangerous if proper safety rules are not followed at all times. In order to prepare your self for a safe year in the laboratory, read over the following safety rules. Then read them a second time. Make sure you understand each rule. If you do not, ask your teacher to explain any rules you are unsure of. You may even want to suggest further rules in the section labeled "Other Rules". When you are satisfied that you understand all the rules on this list, sign and date the contract in the place provided. Signing this contract tells your teacher that you are aware of the rules of the laboratory.

A. Dress Code
1. Many materials in the laboratory can cause eye injury. To protect yourself from possible injury, always wear safety goggles or glasses whenever you are working with chemicals, burners, or any substance that might get into your eyes.

2. Laboratory aprons or coats should also be worn whenever working with chemicals or heated substances.

3. Tie back long hair in order to keep it away from any chemicals, burners, and candles, or other laboratory equipment.

4. Any article of clothing or jewelry that can hang down and touch chemicals and flames should be removed or tied back before working in the laboratory. Sleeves should be rolled up.

5. Sandals will not protect the feet.

B. General Safety Rules
1. Read all directions for an experiment several times. Follow the directions exactly as they are written. If you are in doubt about any part of the experiment, ask your teacher for assistance.

2. Never perform activities that are not authorized by your teacher. Always obtain permission before "experimenting" on your own.

3. Never handle any equipment unless you have specific permission.

4. Take extreme care not to spill any material in the laboratory. If spills occur, ask your teacher immediately about the proper clean-up procedure. Never simply pour chemicals or other substances into the sink or trash container.

5. Never eat or drink in the laboratory. Wash your hands before and after each experiment.

6. There should be no loud talking or horseplay in the laboratory.

7. When performing a lab, make sure the work area has been cleared of purses, books, jackets, etc.

8. Know the location and use of all safety equipment (goggles, aprons, eyewash, fire blanket, fire extinguishers, etc.)

9. Read your assignment before coming to class and be aware of all safety precautions. Follow directions.

10. Never work alone in the lab.

C. Heating and Fire Safety
1. Again, never use any heat source such as a candle or burner without wearing safety goggles.

2. Never heat any chemical that you are not instructed to heat. A chemical that is harmless when cool can be dangerous when heated.

3. Always maintain a clean work area and keep all materials away from flames. Never leave a flame unattended.

4. Never reach across a flame.

5. Make sure you know how to light a Bunsen burner. (Your teacher will demonstrate the proper procedure for lighting a burner.) If the flame leaps out of a burner towards you, turn the gas off immediately. Do not touch the burner. It may be hot. And never leave a lighted burner unattended!

6. Always point a test tube that is being heated away from you and others. Chemicals can splash or boil out of a heated test tube.

7. Never heat a liquid in a closed container. The expanding gases produced may blow the container apart, injuring you or others.

8. Never pick up any container that has been heated without first holding the back of your hand near it. If you can feel the heat on the back of your hand, the container may be too hot to handle. Always use a clamp or tongs when handling hot containers. Hot glassware looks the same as cool glassware.

D. Using Chemicals Safely
1. Never mix chemicals for the "fun of it." You might produce a dangerous, possibly explosive substance. No unauthorized experiments should be performed.

2. Never touch, taste, or smell any chemical that you do not know for a fact is harmless. Many chemicals are poisonous. If you are instructed to note the fumes in an experiment, always gently wave your hand over the opening of a container and direct the fumes toward your nose. Do not inhale the fumes directly from the container.

3. Use only those chemicals needed in the activity. Keep all lids closed when a chemical is not being used. Notify your teacher when chemicals are spilled.

4. Dispose of all chemicals as instructed by your teacher.

5. Be extra careful when working with acids or bases. Pour such chemicals over the sink, not over your work bench.

6. When diluting an acid, always pour the acid into water. Never pour water into the acid.

7. Rinse any acids off your skin or clothing with water. Immediately notify your teacher of any acid spill.

8. Never pipet by mouth.

9. Be sure you use the correct chemical. Read the label twice.

10. Do not return any excess back to the reagent bottle.

11. Do not contaminate the chemical supply.

12. Keep combustible materials away from open flames (alcohol, carbon disulfide, and acetone are combustible).

13. Do NOT use the same spatula to remove chemicals from two different containers. Each container should have a different spatula.

14. When you remove the stopper from a bottle, do NOT lay it down on the desk, but place the stopper between your two fingers and hold the bottle so the label is in the palm of your hand so drips won't ruin the label, etc. Both the bottle and the stopper will be held in one hand. Be sure and rinse any drips that might have gotten on the outside of the bottle.

15. Be careful not to interchange stoppers from two different containers

16. Replace all stoppers and caps on the bottle as soon as you finish using it.

17. Mercury spills must be cleaned up immediately. Use the new mercury sponge clean up kits put out by various companies.

E. Using Glassware Safely
1. Glass tubing should never be forced into a rubber stopper. A turning motion and lubricant will be helpful when inserting glass tubing into rubber stoppers or rubber tubing. Your teacher will demonstrate the proper way to insert glass tubing.

2. When heating glassware, use a wire or ceramic screen to protect glassware from the flame of a Bunsen burner.

3. If you are instructed to cut glass tubing, always fire polishes the ends immediately to remove sharp edges.

4. Never use broken or chipped glassware. If glassware breaks, notify your teacher and dispose of the glassware in the proper trash container.

5. Never eat or drink from laboratory glassware. Always thoroughly clean glassware before putting it away.

F. Using Sharp Instruments
1. Handle scalpels or razor blades with extreme care. Never cut any material towards you: always cut away from you.

2. Notify your teacher immediately if you are cut in the laboratory.

3. Properly mount, dissecting specimens to the dissecting pan before making a cut.

G. Electrical Equipment Rules
1. Batteries should never be intentionally shorted. Severe burns can be caused by the heat generated in a bare copper wire placed directly across the battery terminals. If a mercury type dry cell is shorted, an explosion can result.

2. Never deliberately shock yourself or another person. Susceptibility to shock and possible resulting injury is unpredictable because of the many physical and physiological variables.

3. Turn off all power when setting up circuits or repairing electrical equipment.

4. Never use such metal articles as metal rulers, metal pencils or pens, nor wear rings, metal watchbands, bracelets, etc. when doing electrical work.

5. When disconnecting a piece of electrical equipment, pull the plug and not the wire.

6. Use caution in handling electrical equipment which has been in use and has been disconnected. The equipment may still be hot enough to produce a serious burn.

7. Never connect, disconnect, or operate a piece of electrical equipment with wet hands or while standing on a wet floor.

H. End-of-Experiment Rules
1. When an experiment is completed, always clean up your work area and return all equipment to its proper place.

2. Wash your hands after every experiment.

3. Make sure all candles and burners are turned off before leaving the laboratory. Check that the gas line leading to the burner is off as well.

I. Other Safety Rules
1. Do not use hair spray or hair mousse during or even before coming to laboratory class. These are highly flammable and might cause automatic ignition when in close proximity to a heat source.

2. Synthetic fingernails are also highly flammable and should not be worn in the lab.