BioEd Online

Researchers involved in a unusual project to prevent natural disasters in two African lakes say the first few years of the attempt have gone well, but have not yet made things safe.

The project aims to remove dangerous levels of carbon dioxide from the bottom of two lakes sitting over volcanic sites in Cameroon. One of these, Lake Nyos, exploded in 1986, suffocating more than 1,700 people in the surrounding area with a plume of carbon dioxide.

After the explosion, scientists realized that a landslide or some other event had caused water rich in carbon dioxide to rise from the safety of the deeps. As its pressure decreased, the rising water released the gas dissolved within it, in the same way that bubbles form in champagne once the bottle is opened. As a result, the water shot to the surface, suddenly releasing fatal amounts of carbon dioxide into the atmosphere.

Pipe dreams

To solve the problem, an international team decided to pipe out the carbon dioxide-rich water in a controlled way. The first pipe was installed in 2001 in Lake Nyos. Another pipe was deployed in 2003 in nearby Lake Monoun, which killed about 40 people when it exploded in 1984.

Some worried that the pipes would destabilize the lakes and cause another dangerous release of carbon dioxide. This prompted the installation of a webcam to monitor the Lake Nyos pipe, and a system to shut down the pipe remotely in case of problems.

Keep a lid on it

In both lakes, a warm, light layer of water stays on the surface, acting as a cap for the gas-heavy water below. This keeps the carbon dioxide-rich water locked up in depths below about 40 metres. Although gas continues to seep into the lowest waters owing to volcanic activity, it stays dissolved thanks to the high pressures. Thankfully the pipes have not altered this situation, reports George Kling of the University of Michigan in Ann Arbor and colleagues in the Proceedings of the National Academy of Sciences¹.

Samuel Freeth, a geochemist at University of Wales, Swansea, who had been concerned that the pipes would not be safe, says that it now “looks as though nothing is likely to happen”. But, he adds, “I still feel the lake should be treated with great care.”

The single pipes have reduced the lakes' carbon dioxide content by 12-14% compared with levels right before they were installed, Kling says. But that's not enough, he adds. Right now, there is thought to be more carbon dioxide in the lakes than was released 20 years ago.

Only a reduction of 80-90% will ensure that a similar explosion won't happen again, says Kling, but the pipes become less efficient as the gas pressure decreases.

Extra outlets

"The modelling shows that in another five years with four more pipes Lake Nyos would be degassed to safe levels," Kling says. "In Monoun it would take two years with one more pipe." Safe levels are reached once the gas pressure is the same as the atmospheric pressure at the lake surface.

The research team had always planned to install more pipes, but that will cost between US$1 million and $2 million. "If anyone reading this has a friend at a foundation or a very rich uncle, we'd be happy to hear from them," Kling says.

And Lake Nyos faces further problems. A dam at the lake's edge is weakening; if it gives, the leak could lower the lake's water level by 40 metres, causing a flood that would affect 5,000 people.

The lake could be drained to prevent this, but Kling points out that the carbon dioxide would have to be safely siphoned off first.