A Cloud of Gas Erupts from Lake Nyos

On the evening of 21 August 1986, a sudden limnic eruption occurred at Lake Nyos, a volcanic crater lake in the highlands of northwestern Cameroon. Deep within the lake, enormous quantities of dissolved carbon dioxide had accumulated over time, held in solution by the intense hydrostatic pressure of the lower water layers. When this stratification was abruptly disturbed, between 100,000 and 300,000 tons of the gas broke out of solution in a violent chain reaction. Roughly a cubic kilometre of gas escaped into the atmosphere, throwing water and foam as high as 80 to 100 metres and generating a lake wave at least 25 metres high that stripped vegetation from the surrounding shores.

The physical appearance of the lake altered drastically overnight. The surface waters, normally clear blue, turned a murky deep red as bottom waters rich in dissolved iron rose to the top and oxidised upon contact with the open air. The lake level dropped by approximately one metre, and adjacent trees were flattened by the violent disturbance. Although scientists have proposed several possible triggers for the initial turnover, including a rockfall, heavy rainfall cooling one section of the lake, or a small volcanic disturbance on the lakebed, other researchers maintain that no external shock was required. Due to the physical properties of carbon dioxide diffusion, the supersaturated deep water can spontaneously destabilise once rising bubbles begin to draw up adjacent water layers.