Lake Nyos is the Cameroonian lake known for a deadly carbon dioxide release in 1986.
On 21 August 1986, a sudden release of dissolved carbon dioxide from the lake created a dense, invisible gas cloud. The gas flowed down nearby valleys, suffocating at least 1,700 people and thousands of animals. The event is called a limnic eruption.
Lake Nyos sits inside a volcanic crater in Cameroon’s Northwest Region. Carbon dioxide from volcanic activity had accumulated in the deep water under pressure. A disturbance caused the gas-rich water to rise, allowing the carbon dioxide to escape rapidly. Because the gas is heavier than air, it spread close to the ground rather than dispersing harmlessly overhead.
Lake Monoun, another Cameroonian crater lake, experienced a similar but smaller disaster in 1984. That similarity makes Lake Monoun a plausible distractor, but the famous 1986 tragedy specifically occurred at Lake Nyos. Engineers later installed pipes to release deep carbon dioxide gradually and reduce the danger of another buildup.