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The Lake Nyos tragedy was a disaster that occurred on August 21, 1986, when a cloud of carbon dioxide gas suddenly boiled at Lake Nyos, Cameroon, killing over 1700 people within a radius of 20 km. The gas killed humans and animals by suffocation.
Chemical engineers concluded that the lake suddenly turned over, bringing dissolved carbon dioxide to the lake surface. The gas was first speculated to be hydrogen sulfide.
Lake Nyos is a deep volcanic crater lake that is thermally stratified, layers of warm, less dense water near the surface float on the colder, denser water layers near the lake's bottom. Over long periods, carbon dioxide gas seeping from underground lava dissolved into the cold water at the lake's bottom and dissolved in great amounts because of the large pressure of CO2 present.
On 21 August, the water became over-saturated with CO2, resulting in gas coming out of solution bubbling up to the surface; this caused the water to turn over, bringing more of the saturated water to surface levels where it was no longer under pressure, releasing further gas. This rapidly released enormous amounts of the gas which suffocated life throughout the region. This was a chilling illustration of Henry's Law; see also Raoult's law.
International efforts have since installed a pipe running from the surface anchored to a raft that allows the deeper areas of the lake to release their CO2 to the surface in controlled small amounts. It is hoped this will reduce the maximum levels of CO2 in the future, and prevent any possibility of the lake turning over. Degassing began in 2001 and is continuing steadily.
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