Current efforts to prevent two lakes in northwestern Cameroon from releasing toxic gasses and killing nearby inhabitants, as they have done in the past, are insufficient, say researchers.
Despite efforts to remove carbon dioxide from Lakes Nyos and Monoun, their waters are already saturated with the gas, creating the risk of a potentially lethal eruption.
In August 1984, Lake Monoun released a cloud of carbon dioxide that asphyxiated 37 people. Two years later, a large cloud erupted from Lake Nyos in an 80-metre fountain. The gas, which is heavier than air, rolled down two nearby valleys, suffocating 1,700 people.
Both lakes sit on pockets of magma in the earth's crust that bubble carbon dioxide into their waters. The gas accumulates at the bottom of the lake until it saturates and bursts into the atmosphere, or until a sudden geological shift — such as a landslide — forces it to the surface.
To prevent either of these events from happening again, researchers placed a pipe in Lake Nyos in 2001 and in Lake Monoun in 2003. The pipes channel the gas up to the surface, releasing it into the air.
But in a paper published online yesterday (26 September) Georges Kling of the US-based University of Michigan and colleagues argue that the pipes are insufficient to carry out the tasks for which they were intended.
In the 15 years between the last gas eruptions and the installation of the pipes, the lakes recharged "at alarming rates", says Kling.
The pipes, he explains, are not evacuating this accumulated gas fast enough, and as a result Lake Nyos now contains more carbon dioxide than was released in 1986.
A large landslide could make this gas burst out of the lake at any moment.
|The degassing pipe at Lake Nyos|
brings a fountain of deep water
to the surface
Kling and his colleagues estimate that, at the current rate, it will take a decade to evacuate the accumulated gas. "That's a huge window of vulnerability for the surrounding populations," he says.
Kling and his colleagues say that nearly all of the carbon dioxide could be removed by 2010 if Lake Monoun had just one additional pipe and Lake Nyos had another four.
This would require an investment of US$1-2 million, says Kling.
"We've known about this problem for a long time, but over the years it has proven difficult to find the funds," he says. The funding for the existing pipes came from a consortium of governments including the Cameroonian, French, Japanese and US governments.
The situation at Lake Monoun is improving. Kling's collaborator in Cameroon, Greg Tanyileke, says that the materials and funding are in place for a second pipe, to be installed there by 2006.
Lake Nyos, however, presents an additional problem. One of its sides is contained by a natural dam that is gradually getting weaker.
Dam experts have told Kling that it could break "any day now". The resulting flood would stretch all the way into Nigeria.
One option to prevent this from happening would be to lower the water level in Lake Nyos by 40 metres. But this would release part of the pressure that is holding the carbon dioxide in place at the bottom of the lake, triggering another gas burst.
What's more, the same gas burst could cause the dam to break.
"We need another push from the donor community," concludes Kling.
Kling and colleagues' research was published online yesterday (26 September) by the Proceedings of the National Academy of Sciences.