On the evening of August 21, 1986, a silent natural disaster unfolded at Lake Nyos, a deep crater lake situated atop a volcanic field in northwestern Cameroon. Without warning, the lake released approximately 1. 6 million tons of carbon dioxide into the surrounding valleys, suffocating over 1,700 people and thousands of livestock within minutes.
The disaster was caused by a rare geophysical phenomenon called a limnic eruption, or lake overturn. Lake Nyos is meromictic, meaning its deep and shallow water layers do not naturally mix. Magma beneath the crater continually dissolved massive quantities of carbon dioxide into the cold, high-pressure waters at the lake bottom, creating a supersaturated solution.
Over years, hydrostatic pressure kept the gas trapped under immense pressure. On that August night, a trigger—likely a small landslide or localized thermal disturbance—displaced deep water upward. As dissolved CO2 rose, hydrostatic pressure decreased, causing the gas to rapidly effervesce out of solution in a runaway chain reaction analogous to uncorking a shaken champagne bottle.
The sudden release displaced over 80 meters of water, triggering a small tsunami while sending a dense CO2 gas cloud cascading down nearby valleys, displacing breathable oxygen.