How did Lake Nyos suddenly kill 1,700 people?

        Science | Geophysics

Degassing Lakes with Big Straws

­After Lake Nyos burst, an international team began discussing ways to degas bot­h lakes and avert future disasters. They talked about bombing the lakes to blow out the gas. But scientists worried a bomb would also blow out one of Lake Nyos's walls, causing an enormous flood. "That would be a disaster in its own right," says Evans. As early as November 1986, French scientists proposed a pipe.

"The pipe idea won out because it's simple, and there's not much risk associated with it," says Evans. "You could eliminate the gas in a controlled fashion."

Pipes were slow to be installed. Money and roads into Nyos weren't plentiful. "When we left Cameroon in 1986, we were certain that we had done good science, recommended how to fix the problem and said aid groups will come in next week and start piping the gas out. It was a wake-up call for all of us for how long this type of stuff takes," says Evans.

The first pipe went into Lake Nyos in 2001. A French engineering team sunk a 6-inch (15-centimeter) plastic tube 666 feet (203 meters) into the lake until it reached the gas layer [source: Halbwachs]. Again, froth shot out like champagne from an uncorked bottle, but this time it wasn't a deadly surprise.

Today, Nyos is degassed to about 80 percent of the level after the 1986 explosion, says Evans. "The lake is safer today than it was in 2000, but it is still hazardous." A big enough input of energy, like a large earthquake or a landslide, could cause the lake to erupt, he says.

Another problem is Nyos' weak wall. "That natural dam could rupture any day," says Evans. "If the dam were to suddenly fail, the upper 40 meters [131 feet] of the lake would empty in a huge flood, and that would release the pressure on the gas remaining in the deep water. You could have a combination of a flood and a gas release." Evans says the gas should be piped out as soon as possible, and then the wall should be fixed. Two more pipes are planned, with the first possibly going in in spring 2009.

Lake Monoun has three pipes: one installed in 2003 and two in 2006. "Another eruption is probably not possible there, given that the lake is almost completely degassed," says Evans. "Monoun now would be a very nice place to live."

­So the next time ­you smell the sulfurous gas as your local lake turns over, think of it as a lake exhalation -- and be thankful that it's not a burp.