https://en.wikipedia.org/wiki/Lake_Nyos
On August 21, 1986, a limnic eruption occurred at Lake Nyos, triggering the sudden release of about 100,000–300,000 tons[10] (some sources state as much as 1.6 million tons)[11] of CO2. This gas cloud rose at nearly 100 kilometres per hour (62 mph) and[4] spilled over the northern lip of the lake into a valley running roughly east-west from Cha to Subum. It then rushed down two valleys branching off to the north, displacing all of the air and suffocating some 1,700 people within 25 kilometres (16 mi) of the lake, mostly rural villagers, as well as 3,500 livestock. The villages most affected were Cha, Nyos, and Subum.[12] Scientists concluded from evidence that a 100 m (330 ft) fountain of water and foam formed at the surface of the lake. The huge amount of water rising suddenly caused much turbulence in the water, spawning a wave of at least 25 metres (82 ft) that would scour the shore of one side.[13]