It’s one of the rarest forms of volcanic activity—and among the most lethal. A limnic eruption occurs when a dangerous gas trapped at the bottom of a volcanic lake suddenly turns over and then escapes. This gas, carbon dioxide, is heavier than air. It’s also colorless, odorless, and impossible to breathe. One limnic eruption at Lake Nyos in Cameroon, Africa, in August 1986 asphyxiated 1,700 people and 3,500 livestock overnight. This event alerted scientists to the threat and led them on a campaign to study and stop these killer lakes—before history repeats itself.
