What happened at Lake Nyos on the night of the 21st of August 1986

The CO₂ Limnic Eruption Theory

Volcanoes are well known as producers of poisonous or asphyxiating gases and, in some instances, these gases kill people caught in the volcanic plumes such was the case on Dieng Plateau in Central Java, Indonesia, where 149 people died in 1979, in the wake of a comparatively minor phreatic eruption - an eruption driven by the vaporisation of groundwater, without any ejection of magmatic material. The possibility that a phreatic eruption occurred through the Cameroonian lakes cannot be completely ruled out. However, in these cases, the culprit could well have been the lake itself: indeed, the possibility that the Monoun gas bursts originated from huge amounts of carbon dioxide dissolved in the deep layers of the lake was first investigated by H. Sigurdsson and his team, who concluded that a disturbance of unknown origin had upset the density stratification of the water column, triggering an overturn of the lake and the subsequent release of carbon dioxide. Being denser than air, CO₂ flows over the ground surface, asphyxiating people unfortunately present in the gas cloud.