Poisonous gas from African lake poses threat to millions

More than two million people living on the banks of Lake Kivu in central Africa are at risk of being asphyxiated by gases building up beneath its surface, scientists have warned.It is estimated that the lake, which straddles the borders of the Democratic Republic of Congo and Rwanda, now contains 300 cubic kilometres of carbon dioxide and 60 cubic kilometres of methane that have bubbled into the Kivu from volcanic vents. The gases are trapped in layers 80 metres below the lake's surface by the intense water pressures there. However, researchers have warned that geological or volcanic events could disturb these waters and release the gases.