How the oil has spread

Approximate oil locations 22 April - 15 May A US Coast Guard official says if leaks from an oil well in the Gulf of Mexico are not stemmed soon, they could cause one of the worst spills in US history. Rear Adm Mary Landry, who is in charge of the government clean-up effort, said work on sealing the leaks using several robotic submersibles could take months. About 1,000 barrels (42,000 gallons) of oil a day are gushing into the sea. An investigation has been ordered into the cause of the leak, which began when an oil rig exploded and sank last week. The joint investigation, by the interior and homeland security departments, will have the power to compel witnesses to testify, and will look into possible violations by the operators of the rig, Transocean. Evacuation Eleven of the rig's workers are still missing and presumed dead in the disaster off the Louisiana coast. OIL SPILL DISASTERS 1991: 520m gallons were deliberately released from Iraqi oil tankers during the first Gulf War to impede the US invasion 1979: 140m gallons were spilt over nine months after a well blow-out in the Bay of Campeche off Mexico's coast 1979: 90m gallons leaked from a Greek oil tanker after it collided with another ship off the coast of Trinidad 1983: 80m gallons leaked into the Gulf over several months after a tanker collided with a drilling platform 1989: 11m gallons were spilt into Alaska's Prince William Sound in the Exxon Valdez disaster

Earth Watch: Oil and water Workers on a nearby oil platform were evacuated by the US authorities on Monday after the oil slick came dangerously close. The leaks - about 5,000ft (1,525m) under the surface - were found on Saturday, four days after the Deepwater Horizon platform, to which the pipe was attached, exploded and sank. The resulting oil slick now has a circumference of about 600 miles (970km) and covers about 28,600 sq miles (74,100 sq km). British oil company BP, one of the firms operating the rig, has not been able to activate a device known as a blow-out preventer, designed to stop oil flow in an emergency. Doug Suttles, the chief operating officer for exploration and production at BP, said it had not yet given up on engaging the valve, but was considering other possible solutions. These include placing a dome directly over the leaks to catch the oil and send it up to the surface, where it could be collected by ships. This has only been done in shallow water before and is still two to four weeks from being operational. BP will also begin drilling a "relief well" intersecting the original well, but it is also experimental and could take two to three months to stop the flow. Forty-nine vessels - oil skimmers, tugboats barges and special recovery boats that separate oil from water - were meanwhile working to round up oil, BP said.

At a news conference, Adm Landry warned that if the well was not secured soon, "this could be one of the most significant oil spills in US history". 'Controlled burn' The current leak would have to continue for more than eight months to match the 11m-gallon spill from the oil tanker Exxon Valdez off Alaska in 1989. Adm Landry said the Coast Guard was considering a "controlled burn" of the petroleum trapped by special containment booms on the surface. Environmental experts warn that animals nearby might be affected by toxic fumes, but perhaps not as much as if they were coated in oil. "We fully understand there are benefits and tradeoffs," Adm Landry said. But she noted that with the spill moving toward land, the impact on Louisiana's coastline, which contains some 40% of the nation's wetlands and spawning grounds for countless fish and birds, had to be considered. Controlled burns had been done and tested before, and had been shown to be "effective in burning 50 to 95% of oil collected in a fire boom", she said. The downside was a "black plume" of smoke, she added. The slick is now about 20 miles (32km) off the coast of Louisiana, but wind projections indicate it will not reach land before Saturday.



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