Reuters -- A natural dam holding back the water of Cameroon's Lake Nyos, where hundreds were killed in a 1986 poison gas disaster, is not solid and could collapse in a decade, putting thousands at risk, United Nations experts said.
After a three-day inspection, Olaf Van Duin and Nisa Nurmohamed of the Netherlands Ministry of Transport and Public Works reported weaknesses in the volcanic rock barrier at the lip of the lake in northwest Cameroon.
They confirmed surveyors' warnings that erosion has been rapidly undermining the dam at Lake Nyos, where a cloud of carbon dioxide that had built up in the water escaped in August 1986, killing 1,800 people in surrounding villages.
"We've seen that the dam structure is not safe ... actually we expect it to breach within 10 to 20 years," Van Duin told Reuters in Yaounde late on Tuesday.
Geologists say that if the dam were to break, it could send a wall of water downhill through Cameroon and into neighbouring Nigeria, submerging an estimated 10,000 people as well as animals and crops.
It might also release another cloud of poison gas, which is stored in the lake's deeper layers.
Van Duin and Nurmohamed said fractures, cracks and holes were visible in the dam structure. Repeated landslides had torn away rock and soil from its outer side and soil had also been eroded from the lake side of the dam, causing cave-ins.
"We are concerned that in time it is going to collapse," Nurmohamed said.
The U.N. experts' visit followed debate among scientists in Cameroon about the timeframe for an eventual collapse of the dam. While some say it could happen at any moment, especially if a volcanic tremor occurs, others argue it will take longer.
Van Duin and Nurmohamed, who will report their findings to the Cameroon government and the U.N. Development Programme, recommended that the easiest and cheapest way to make the dam safer would be to reduce water pressure by lowering the water level by about 20 meters.
This could be done by installing giant pipes to pump water out of the lake.
Building a new artificial dam to strengthen the natural barrier could take a long time and be costly, the experts said.
Efforts have been made to drain carbon dioxide from the lake but scientists say more work needs to be done to reinforce the dam and accelerate the degassing. Cameroon officials say a lack of money has delayed progress.
Scientists say Lake Nyos is one of only three lakes in the world known to be saturated with carbon dioxide -- along with Lake Monoun, also in Cameroon, and Lake Kivu on Rwanda's border with Democratic Republic of Congo.
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