Can a lake kill?

The “exploding” lakes phenomenon is real, with more and more scientific evidence supporting the notion that lakes have the power to kill.

So where are these deadly lakes? And what are scientists doing to prevent more deaths?

On Aug. 21, 1986, Cameroon’s Lake Nyos unexpectedly “exploded,” releasing a toxic cloud of carbon dioxide that suffocated 1,700 people in the surrounding area.

A similar disaster happened in August 1984 at another Cameroon lake — Lake Monoun — killing 37 people.

“Exploding” lakes are crater lakes formed by volcanic eruptions. They are caused by a buildup of CO2 gas in the lake’s bottom waters, says Bill Evans, a chemist with the U.S. Geological Survey, who has been studying the two West African lakes for decades.

Over time, CO2 gas seeps into the lakes from magma below. Magmas are known to release gas for thousands of years after a volcanic eruption, and Cameroon is a volcanically active country.

When an event such as a landside occurs, the CO2 buildup at the bottom of the lake is disturbed, triggering the mixture of bottom water and gas to rise toward the surface, says Evans.

Once the gas depressurizes, bubbles form and that decreases the density of the water, creating a “self-sustaining degassing process that gets bigger and more violent as time goes on,” he says.

There are only three known “exploding” lakes in the world: the two in Cameroon and East Africa’s Lake Kivu, which borders Rwanda and the Democratic Republic of Congo. Unlike Cameroon’s lakes, Kivu has not exploded in historical times.

Evans has been monitoring the Cameroon lakes since the mid-1980s, when he was sent to West Africa to investigate the disasters as part of an international group.

He visited Lake Nyos 10 days after the 1986 explosion.

The scientists collected data — interviewing doctors who handled the dead, collecting water samples and the lake’s temperature and monitoring vegetation — to rule out the possibility that the Nyos disaster wasn’t due to a volcanic eruption.

“I think the real wake-up call for us came when we got a boat on the lake,” Evans says. “It looked like Campbell’s tomato soup.” The lake had turned red because of the oxidized iron in the water. It took eight months for Nyos to return to its normal colour.

The CO2 cloud that formed over the lake within several hours after the “explosion” eventually drifted down slope killing people in the surrounding river valleys.

“People can lose consciousness after just two breaths of CO2, and that is likely what happened at Nyos. People just fell in the middle of their evening activities,” Evans says.

“One woman hanging laundry was found still clutching the corners of the sheet she was about to hang.”

In 2001 a French engineering team installed pipes in Lake Nyos to degas the lake. The pipes allow the bottom water to rise up at a controlled rate and release the CO2 slowly and safely into the air.

Similar pipes were installed in Lake Monoun in 2003. By 2010 the small lake had been degassed to safe levels.

Other scientists are active at Lake Kivu, which has CO2 and methane gas, to look at ways to monitor and extract its gas.

Evans predicts Lake Nyos — which is roughly 210 metres deep and one kilometre in diameter — will reach to safe levels by 2022.

The fear of another explosion happening there, however, is still real.

Between 1986 and 2001 scientists watched the pressure of CO2 gas in the very deepest part of Lake Nyos double, says Evans.

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He estimates it would take about 100 years to saturate Lake Nyos with CO2 gas if pipes weren’t put in place.

“At Nyos I think we’ve got a ways to go before we would want to call it safe,” Evans says. “Monoun currently is safe. Of course the problem is that once these pipes are pulled out of the lake. . . that process of (CO2) buildup starts again.

“Technically, maybe it takes 100 years, but the lake will become dangerous again.”