How dangerous is Africa’s explosive Lake Kivu?

An unusual lake in central Africa could one day release a vast cloud of greenhouse gases that suffocates millions of people. But it’s not clear whether the threat is getting worse.

On 22 May, one of Africa’s most active volcanoes, Mount Nyiragongo, started spewing lava towards the crowded city of Goma in the Democratic Republic of the Congo (DRC). The eruption destroyed several villages, killed dozens of people and forced an estimated 450,000 people to flee their homes.

The volcano has since calmed and the immediate humanitarian crisis has eased. But government officials and scientists have another worry on their minds: something potentially even more dangerous than Mount Nyiragongo.

Goma sits on the shore of Lake Kivu, a geological anomaly that holds 300 cubic kilometres of dissolved carbon dioxide and 60 cubic kilometres of methane, laced with toxic hydrogen sulfide. The picturesque lake, nestled between the DRC and Rwanda, has the potential to explosively release these gases in a rare phenomenon known as a limnic eruption. That could send a huge pulse of heat-trapping gases into the atmosphere: the lake holds the equivalent of 2.6 gigatonnes of CO2, which is equal to about 5% of global annual greenhouse-gas emissions. Even worse, such a disaster could fill the surrounding valley with suffocating and toxic gas, potentially killing millions of people. “It could create one of the worst, if not the worst, natural humanitarian disasters in history,” says Philip Morkel, an engineer and founder of Hydragas Energy, based in North Vancouver, Canada, who is attempting to get funding for a project to remove and utilize gas from the lake.

The 2021 volcanic eruption didn’t trigger a mass release of gases from the lake, and on 1 June, the Rwanda Environment Management Authority (REMA) said there was no imminent risk. But, the authorities do think that lava flowed through underground fractures beneath the city of Goma and Lake Kivu itself. A day after the eruption, a tremor seems to have triggered part of a sandbar by the lake to collapse, which might have caused a small release of gases in that spot: some people reported that waters offshore from a prominent hotel looked like they were boiling.

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