Geochemical study of CO_2 build-up in Lake Nyos, Cameroon

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The gas outburst from Lake Nyos in 1986 and a similar event at Lake Monoun in 1984, both in Cameroon, West Africa, killed approximately 1800 people and several thousand animals. Death resulted from the exsolution of magmatic CO_2 dissolved in the bottom layers of these two crater lakes. Since the volcanoes which host the lakes have neither the records of eruption nor geothermal manifestation, these gas disasters can be regarded as "cold" volcanic hazards and a new type natural disaster.Seven years of continuous observation of these lakes following the dramatic events have revealed that (1) the gas disasters were caused by a massive release of carbon dioxide dissolved in the lakes ; and not by a volcanic phreatic eruption, (2) the carbon dioxide is supplied to the lake bottoms in the form of warm CO_2-charged mineralized springs, (3) the gas build-up and subsequent release was highly conditioned by the density structure of the lakes, (4) the CO_2 build-up within the bottom layers of Lake Nyos is increasing at an alarming rate, and (5) the recurrence of similar gas bursts from the lakes is, therefore, highly probable ; but can effectively be prevented.Based on the above findings, the following remedial actions should be undertaken as soon as possible so as to alleviate the dangers from future gas bursts. (1) The lakes should be degassed. Controlled degassing, initiated but halted due to funding constraints, should be encouraged. (2) Deep tropical lakes with a similar recharge system have the potential to accumulate CO_2 and other gasses. Regular geochemical and limnological surveys of tropical volcanic lakes are, therefore, highly recommended as a mitigative measure against the Nyos-type disasters.