The Lake Nyos disaster occurred on 21 August 1986, when a limnic eruption at Lake Nyos, in northwestern Cameroon, produced a large cloud of carbon dioxide (CO2), which descended onto nearby villages, killing 1,700 people and 3,500 livestock.
The eruption triggered the sudden release of about 100,000–300,000 tons (some sources state as much as 1.6 million tons) of CO2. This gas cloud rose at nearly 100 kilometres per hour (62 mph) and spilled over the northern lip of the lake. It then rushed down two valleys, branching off to the north, displacing all the air and suffocating people and livestock within 25 kilometres (16 mi) of the lake.
A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in deep waters and therefore the risk of further eruptions.