In 1986, a volcanic lake (Lake Nyos) in Cameroon, Africa burped a C02 gas cloud that killed 1,746 people in minutes.
The CO2-rich cloud was expelled rapidly from the southern floor of Lake Nyos. It rose as a jet with a speed of about 100 km per hour. The cloud quickly enveloped houses within the crater that was 120 meters above the shoreline of the lake. Because CO2 is about 1.5 times the density of air, the gaseous mass hugged the ground surface and descended valleys along the north side of the crater.
The deadly cloud was about 50 meters thick and it advanced downslope at a rate of 20 to 50 km per hour. This deadly mist persisted in a concentrated form over a distance of 23 km, bringing sudden death to the villages of Nyos, Kam, Cha, and Subum.
The bodies of those that died were generally devoid of trauma. Most victims appeared to have simply fallen asleep and died from asphyxiation. Many died in their beds. One survivor was Joseph Nkwain from Subum. He was awakened at about midnight by a loud noise.