Lake Nyos disaster

On the night of 21 August 1986, a large volume of carbon dioxide escaped from Lake Nyos, a deep crater lake in Cameroon. The gas dispersed into surrounding valleys, where its high concentration displaced breathable air and caused fatal asphyxiation among people and animals. Britannica gives a human death toll of roughly 1,700–1,800. The exact extent and movement of the gas cloud varied across the affected area; many victims were in settlements and routes below the lake.

Lake Nyos lies in a volcanic region and receives carbon dioxide from geological sources. The gas dissolves under pressure in deep lake water, while the lake's stable stratification limits seasonal mixing that might otherwise release it gradually. In 1986, the deep water was sufficiently gas-rich for a rapid overturn or disturbance to bring gas-bearing water upward; as pressure fell, carbon dioxide came out of solution and rose as a gas. Scientists commonly describe the disaster as a limnic eruption. The precise initial trigger remains uncertain; proposed possibilities have included a landslide or other disturbance, and it should not be presented as definitively established.

The disaster led researchers to measure the lake's dissolved gases and stratification, and to consider whether similar hazards existed at other gas-rich volcanic lakes. Controlled degassing at Lake Nyos began in 2001: pipes draw carbon-dioxide-rich deep water upward so that gas escapes in a managed way rather than building up to dangerous levels. Research has documented reduced dissolved carbon dioxide after degassing began, while also showing that geological recharge continues. Monitoring therefore remains important, and degassing is a risk-reduction measure rather than proof that the hazard has permanently disappeared.

Lake Nyos became a key case study of gas accumulation in stratified lakes and the hazards posed by sudden releases. The disaster demonstrated that a lake can release a lethal gas cloud without a conventional volcanic eruption or an explosive impact. It also spurred continuing research into lake chemistry, gas monitoring, and practical engineering measures for communities near volcanic lakes.