On 12 August 1986, a deadly cloud of CO2 and water mist was released from Lake Nyos, Cameroon, and killed more than 1700 people by asphyxiation as it spilled into adjacent valleys. The dense cloud of gas, which was 50 m thick and traveled farther than 20 km at speeds of 20 to 50 km/hour, was produced by the dissolution of CO2 in the deep part of the lake; a convective overturn displaced the lower layer of the stratified lake, causing the CO2-rich water that had been at the bottom to degas like a bottle of fizzy water being opened. Such events have happened before in this region, and may happen again if steps are not taken to prevent them.
Schmid et al. report that a similar situation is developing at Lake Kivu, an East African rift lake between Rwanda and the Democratic Republic of Congo. The depths of Lake Kivu are amassing dissolved CO2 and CH4 at a rate fast enough that CH4 concentrations will approach saturation toward the end of this century, making it likely that a magmatic eruption in the volcanically active lake basin, or some other disturbance, could trigger overturn and the release of another lethal CO2 cloud. Without human intervention to reduce the concentration of CH4, the 2 million people along the Lake Kivu shoreline may suffer a catastrophic gas release. -- HJS
Geochem. Geophys. Geosyst. 10.1029/2004GC000892 (2005).
