Webpage by:
Theresa Kayzar “T.K.”

Geologic Background of Lake Kivu

The “hazard lurking beneath the lake”...

In addition to the external geology of Lake Kivu, the internal stratification is rather remarkable. The general structure of Lake Kivu shows sharp boundaries in vertical temperature and salinity that are explained by separate convecting layers within the lake. The top 200m of the lake consist of freshwater environments; however, the deeper waters of the lake contain large amounts of CO₂ and CH_4; the origin of which is highly debated. It is generally thought that the CO₂ is of volcanic origin and that bacteria within the lake itself produce the renewing reserves of methane (Degens et al, 1973; Lake Kivu, 2002).  In 1973, the levels of CO₂ and CH₄ within Lake Kivu approached but did not exceed saturation, and there was no spontaneous exsolution of these gases (Degens et al, 1973). According to George Kling, a limnologist at the University of Michigan, approximately 200km³ of CO₂ lies at depth, which he refers to as a “hazard lurking beneath the lake” (Witze, 2002). For comparison, the catastrophic eruption of Mt. St. Helens in 1980 produced only 1/3 of a cubic kilometer of ash.

If the gas that is stored at depth within Lake Kivu were to be suddenly released, the gases could asphyxiate local residents of the lake. While scientists have never first-handedly seen a release of this kind, George Kling and Robert Hecky of the University of Michigan provide evidence in sediment cores from the lake showing a catastrophic die-off of living creatures in the lake. This evidence is consistent with a gas release and possible overturning of the lake (Witze, 2002; Lake Kivu, 2002).