Bathymetric map

Origine du gaz

Origin and generation of Methane

The origin of the methane in the Lake Kivu is not fully known . Few hypotheses have been advanced on the processes leading to the formation and the enrichment of the deep water in methane gas and carbon dioxide. The methane gas is believed to form in the Lake from a combination of geological and biological process. Magmatic carbon dioxide (ancient carbon dioxide) is reduced directly by anaerobic bacteria, which proliferate in the stagnant deep waters of the Lake. The same bacteria cause also the decomposition and fermentation of the organic material accumulating in the bottom sediment, leading to the formation of carbon dioxide and methane. Due to volcanic character of the region, the temperature of the Lake increases with depth. The deep warm water is more soluble to minerals than the cool water above it and the weight of the minerals dissolved makes the water at the bottom denser than at the top (in spite of its high temperature). Convection, the normal movement of warm fluids up and cool fluids down, is thus prevented and stability is obtained. Below a depth of about 270 meters , temperatures and pressures are such that the water can absorb substantial quantities of methane and other gases.

Composition and reserves

Based on the recent bathymetric survey undertaken in 1998 by the consulting group LAHMEYER International / OSAE and the gas concentration measurements carried out in 1974/75, the gases in place are:

• Carbon dioxide: 255 billion cum (STP)
• Methane gas: 55 billion cum (STP)
• Nitrogen: 5 billion cum (STP)
• Traces of other gases: Hydrogen sulfide, Ethane, Propane, etc.

The composition of the crude gas is:

• Methane: 24,90 % vol.
• Carbon dioxide: 73,50 %
• Hydrogen sulfide: 0,05%
• Other gases: 1,55%