Deadly gas and flooding continue to pose a threat at Lake Nios in the African nation of Cameroon, where more than 1,700 people were killed by a gas cloud last summer, American scientists said Wednesday in proposing actions to ease the danger.
A series of steps, including lowering the level of Lake Nios and removing dissolved gas from the lake, were recommended in the American scientific team's final report.
An unstable spillway on the lake poses a threat of major flooding in the area, Edward J. Koenigsberg of the U.S. Office of Foreign Disaster Assistance warned at a State Department briefing.
The lake's water still contains high concentrations of dissolved carbon dioxide, raising the possibility of another sudden gas cloud similar to the one that claimed 1,746 lives last Aug. 21, he added. Those victims were smothered by a cloud of carbon dioxide that bubbled out of the lake, the study concluded.
Meeting Next Month
The U.S. team will return to Cameroon next month to meet with local officials and scientists from several other nations to compare findings and proposals for preventing further tragedies, Koenigsberg reported.
While investigators have concluded that the carbon dioxide cloud killed the victims of the disaster, the mechanism that caused it to burst forth from the lake remains in some dispute, Koenigsberg said.
American scientists believe the gas, which originated in molten rock deep in the earth, was dissolved in the bottom layers of the lake and suddenly bubbled forth, the way carbon dioxide bubbles out of a soft drink when the cap is removed. The trigger could have been a storm above the lake, a small landslide, runoff from heavy rains or even seasonal cooling, Koenigsberg said.
Normally, water in lakes like Nios remains very stable, allowing gas concentrations to build up. By contrast, lakes in cooler climates such as the United States have a regular circulation because of seasonal warming and cooling, and that prevents such a buildup.
Carbon dioxide is invisible and generally considered odorless and tasteless. It can be formed from natural chemical reactions, such as in beer and sparkling wine, where it forms the bubbles. It can also originate from molten rock, and the lava underlying volcanoes in Cameroon appears to contain large amounts.
French scientists have a different theory of the cause of the disaster, contending that a huge bubble of gas from deep in the Earth suddenly burst through the lake.
While the cause remains in dispute, Koenigsberg suggested that a major problem continues at a spillway on the lake. Formed of soft, volcanic rock, the spillway is leaking and could collapse, he said, posing a danger of serious floods. A collapse could drop the level of the mile-square lake as much as 120 feet, he said.
Koenigsberg proposed slowly lowering the lake level and then demolishing the spillway.
As for the gas trapped in the lake waters, he said U.S. Environmental Protection Agency officials have proposed a system of deep tubes that could siphon water from the bottom to the surface, allowing carbon dioxide to bubble out gradually. This would take about three years, he said.