Answer:
The Lake Nyos disaster was a limnic eruption that occurred on August 21, 1986, in northwestern Cameroon. The eruption triggered the sudden release of about 100,000-300,000 tons of carbon dioxide (CO2). The gas cloud initially rose at nearly 100 kilometers per hour and then descended onto nearby villages, displacing all the air and suffocating people and livestock within 25 kilometers of the lake.
What triggered the catastrophic outgassing is not known for certain. Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake. A third possibility is that cool rainwater falling on one side of the lake triggered the overturn. Others still believe there was a small earthquake, but because witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely.