It sounds
like a bad horror movie: exploding killer lakes. But such lakes are a reality
in Cameroon, Africa. Scientists there are developing a solution, however, to
stop the natural hazard.
In
1986, Lake Nyos in Cameroon exploded with a deadly cloud of carbon dioxide.
Since then, researchers have been working to lower the carbon dioxide concentration
in the lake by running an exhaust pipe 24 hours a day, expunging the lake of
its extra gas, like the uncorking of a champagne bottle. Image courtesy of George
Kling.
In 1984 and 1986, volcanic lakes Monoun and Nyos, respectively, silently erupted
poisonous columns of carbon dioxide that swept out of their craters and into
the valleys below — asphyxiating thousands of animals and 1,800 people
along the way. “It came as a total surprise to everyone,” says Johan
Varekamp, a geologist at Wesleyan University in Middletown, Conn. “Exploding
lakes were a hazard we didn’t even know about,” he says. Since then,
scientists have found only one other lake with similarly high concentrations
of carbon dioxide and methane: Lake Kivu, also in Africa, may have similarly
burst in the past several thousand years.
The carbon dioxide and methane in Monoun and Nyos, which have reached saturation
levels of 97 percent, originate from magma deep beneath the lakes. The lakes
are layered, with heavy carbon dioxide-laden waters at depth, topped by distinct
layers of successively less concentrated waters. The climate in the area is
not conducive for mixing, so the lakes stay layered unless something disturbs
them, as happened in the 1980s (though scientists still do not know the exact
cause of that disturbance).
The magma provides a continuous gas recharge into the lakes with no natural
outlets, ensuring “a natural cycle of repeating disasters,” says George
Kling, a geologist at the University of Michigan in Ann Arbor. It is not a question
of if the lakes will erupt again, but when, he says. Thus, Kling and colleagues
undertook a project to “degas” the lakes, in hopes of averting a future
disaster.
In 2001, after years of theoretical modeling and with support from the Cameroonian
government and international agencies, an international team installed a pipe
in Lake Nyos to release some of the gas from the lake into the air. Big questions
surrounded the experiment, Kling says: “If we brought up deep, heavy bottom
water, would it sink right back down and cause enough destabilization in the
stratified layers of water to cause another gas explosion?”
When the 50-meter fountain of gaseous water shot out of the pipe like a champagne
bottle popping and Nyos did not immediately explode, the researchers continued
to run the experiment. In 2003, they added a pipe to Lake Monoun. Continuous
monitoring of the gas fountain and of the lake over the past several years supports
that the pipes are not decreasing the stability of the lake, and that the degassing
process is “actually working,” Kling says. Gas content in both lakes
is already lower, and the carbon dioxide dissipates so quickly once it hits
the air that there seems to be no local environmental ramifications, as Kling
and colleagues reported in the Oct. 4 Proceedings of the National Academy of
Sciences.
Still, Kling says, the current pumping rates in the lakes do little to actually
remove the hazard quickly. In Monoun, the pumping rate and pipe depth are such
that in two years, the pipe will be incapable of removing gas faster than it
comes in. And in Nyos, the pipe removes so little gas that it will take decades
to get the lakes to “safe levels,” he says. To significantly reduce
the hazard in the area, Kling’s team recommends the installation of one
more pipe in Monoun, which models indicate would remove 75 percent of the lake’s
carbon dioxide. They also recommend four more pipes in Nyos, which would reduce
the carbon dioxide levels by 99 percent by 2010.
People may always have some concern that stirring up the lake waters through
more pumping might cause gas bursts, says Varekamp, who is not involved with
the research. But, he says, the lakes will explode again unless people step
in. “We can’t stop the San Andreas Fault from quaking, and we can’t
stop a volcano from erupting, but here, in Cameroon, we have an engineered solution”
that could avert the sure disaster of the lakes erupting again.
Megan Sever
Links:
Lake Nyos and Monoun Degassing Project
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