The massive amount of carbon dioxide and methane trapped below a depth of 1,000 feet in Lake Kivu is kept from rising to the surface by the weight and pressure of the lake’s water above.
Carbon dioxide became trapped deep in the lake after seeping through the lakebed from molten rocks below. Bacteria in the lake has converted some of that gas into methane.
Sudden underwater landslides or other geologic activity have the potential to churn the lake enough to send both gases bubbling to the surface.
Since carbon dioxide is heavier than air, it would hug the ground, asphyxiating all humans and animals that it reached.
Such a disaster occurred in 1986 at Lake Nyos in Cameroon, West Africa, where 1,700 people were suffocated, many quietly as they slept.
Lake Kivu contains 350 times as much gas as Nyos and has far more people living near its shoreline. Around a quarter of a million people live at the northern end of the lake in the DRC city of Goma alone.
There have been a few efforts made to extract methane from deep in the lake to be used as fuel for electricity generators.
Some experts say siphoning off methane with pipes lowered from floating platforms could reduce the threat of a deadly upwelling of poisonous gas. But others express concern that such a disturbance to the lake’s natural gas layers could actually trigger disaster.