Gas threat grows from Cameroon's lethal lakes
Perched among the highlands of western Cameroon, bordered by green mountains and cliff faces, Lake Nyos is a scene of breathtaking beauty. But the picture is deceptive. A detailed study reveals that without emergency measures, the lake could release a lethal cloud of carbon dioxide, capable of wiping out entire communities around its shores.
The warning, from a team of scientists, comes nearly 20 years after the lake belched an estimated 80 cubic metres of carbon dioxide into the atmosphere.
Heavier than air, the cloud of gas rolled down surrounding hillsides, engulfing villages. Silent, odourless and invisible, it starved the air of oxygen, asphyxiating hundreds of cattle and claiming the lives of more than 1 700 people up to 26km away.
“It was one of the most baffling disasters scientists have ever investigated. Lakes just don’t rise up and wipe out thousands of people,” said George Kling, an ecologist at the University of Michigan.
Researchers called in after the 1986 tragedy discovered that the lake, which sits atop a volcano, contained record levels of carbon dioxide. Gas bubbling up from the Earth’s magma was under such pressure at the bottom of the 200m-deep lake that it dissolved until it reached saturation point. A slight disturbance then released the dissolved gas as a devastating bubble.
To prevent a recurrence, in 2001 engineers installed a pipe to suck carbon dioxide from the bottom of the lake and release it harmlessly into the air. A similar pipe was also installed at nearby Lake Monoun, where an eruption of carbon dioxide killed 37 people in 1984.
But according to Kling, too little has been done to make the lakes safe. With colleagues at the United States Geological Survey and the Institute for Geological and Mining Research in Cameroon, he spent 12 years testing the carbon-dioxide levels of both lakes.
In Tuesday’s Proceedings of the National Academy of Sciences, they report that without emergency intervention, the lakes are set for further potentially devastating explosions.
“In both lakes, there’s been a 12% to 14% reduction in overall gas content, which is the good news,” said Kling. “The bad news is that the single pipes are not sufficient to rapidly remove as much as is needed to make them safe. There is still more gas in both lakes than was released in the 1980s.
“We could have a gas burst tomorrow that could be bigger than either of those disasters and every day we wait is just an accumulation of the probability that something bad is going to happen.”
Kling’s team recommends the urgent installation of a further four pipes in each lake at a rate of one a year.
“By 2010, those five pipes would be enough to get the carbon dioxide down to safe levels,” he said.
The danger around Lake Nyos has increased in recent years as families evacuated for a generation since the 1986 eruption have started to move back, encouraged by the fertile farmland. The communities around Lake Monoun have expanded, meaning an eruption there could kill more than in the 1980s.—Guardian Unlimited Â