Gas in lake a threat to millions

GOMA - 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 say.

It is estimated that the lake, which straddles the borders of the Democratic Republic of Congo and Rwanda, now contains 300cu km of carbon dioxide and 60cu km of methane that have bubbled into Kivu from volcanic vents.

The gases are trapped in layers 80m 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.

According to a report in the journal Nature this month, the impact would be devastating, as demonstrated on August 21, 1986, at Lake Nyos in Cameroon, in West Africa.

Its waters were saturated with carbon dioxide and a major disturbance - most probably a landslide - caused a huge cloud of carbon dioxide to bubble up from its depths and pour down the valleys that lead from the crater lake.

Carbon dioxide is denser than air, so the 80km/h cloud hugged the ground, suffocating about 1700 people.

Lake Kivu is more than 3000 times the size of Nyos and contains more than 350 times as much gas.

More worrying is the fact that the shores of Kivu are much more heavily populated. About two million people live there, including the 250,000 citizens of the city of Goma, Professor George Kling, of the department of ecology and evolutionary biology at Michigan University, told Nature.

The source of Kivu's problems stems from carbon dioxide that has bubbled up through the lake bed from molten rocks below. The region is a centre of volcanic activity. Some of this carbon dioxide has been converted by bacteria in the lake into methane. Hence the accumulation of both gases.

Engineers are trying to tap Kivu's rich supplies of methane - by lowering pipes from floating platforms down to its holding layers and siphoning off the gas. This could then be burnt and used as a source of industrial and domestic energy.

Tapping Kivu's methane could, theoretically, reduce the risk of a deadly eruption, say engineers. However, scientists have also warned that tampering with the lake's gases also carries a risk of triggering a disaster.

- OBSERVER