Straddling the heavily populated border between Rwanda and the Democratic Republic of Congo, Lake Kivu contains huge amounts of dissolved carbon dioxide and highly combustible methane gas.

Scientists believe the overall danger across the lake as a whole is small, but a pocket of gas in the comparatively shallow Gulf of Kabuno in the north-western corner of the lake may prove more problematic. Just 12 meters below the surface, an estimated three cubic kilometres of carbon dioxide is present, right atop a tectonic faultline. Scientists fear a major earthquake or a large lava flow from a nearby volcano could lead to a giant release of gas from the gulf.

Congo’s environment minister warned on Tuesday that this gas could explode any day, threatening the lives of tens of thousands.

The risk of explosion is imminent,” environment minister Jose Endundo told Reuters in an interview. “It’s like a bottle of Coca-Cola or champagne. If there is too much pressure inside the bottle, it will explode. It’s the same phenomenon.”

In 1986, about 1,700 people were killed in Cameroon as 1,2 million tonnes of carbon dioxide trapped under Lake Nyos was released into the air.

The risk is that this gas escapes and asphyxiates thousands of people. There is an urgent need to evacuate gas from the Gulf of Kabuno, which now holds 10 times the amount of carbon dioxide that Lake Nyos contained,” Endundo said.

Anything is possible, if this cloud is pushed by the wind,” says Michel Halbwachs, a volcanologist and Lake Kivu expert with France’s Universite de Savoie. “We could have a very light scenario or we could have a very heavy scenario. (…) Entire neighbourhoods could be hit.

The shores of the Gulf of Kabuno are home to several large villages, and roughly 20 km to the east is the city of Goma with a resident population of roughly 1 million.

The World Bank has set aside $3 million to fund a project to remove gas from the gulf, but this isn’t enough to complete the project and Congo is therefore currently looking for other sources of finance. Earlier this year, Congo and Rwanda agreed to a joint project to produce 200 megawatts of power from Lake Kivu’s methane reserves. Pumping out the carbon dioxide together with the methane reserves could help alleviate the risk of a disaster. Rwanda is already extracting small amounts of methane from the lake using a demonstration rig. By the end of last year, the rig was producing 2 megawatts of power.