Lake Nyos is a crater lake in the Northwest Province of Cameroon, located about 200 miles (322 km) northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity. On August 21, 1986, a limnic eruption occurred at Lake Nyos which triggered the sudden release of about 1.6 million tonnes of CO2; this cloud rose at nearly 100 kilometres (62 mi) per hour. The gas spilled over the northern lip of the lake into a valley running roughly east-west from Cha to Subum, and then rushed down two valleys branching off it to the north, displacing all 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 worst affected villages were Cha, Nyos, and Subum. Scientists concluded from evidence that a 300-foot (91 m) fountain of water and foam formed at the surface of the lake.