Nairobi — Over two million people who live on the shores of Lake Kivu on the border of Rwanda and the Democratic Republic of Congo could be at risk if hundreds of cubic kilometres of carbon dioxide and methane stored deep within the lake are released.

According to recent scientific studies both by Swiss and American experts, the large quantities of potentially toxic gases stored under the lake are at risk either from another volcanic explosion or earth tremors, which are a frequent occurence in the Great Rift Valley.

The gases are at present compressed in layers around 80 metres below the lake's surface by the intense water pressure there.

But scientists are warning that earth tremors could dislodge the gases, leading to their release into the atmosphere.

They point to a the tragedy at Lake Nyos in Cameroon in 1986 when, following a landslide, a huge cloud of carbon dioxide bubbled up to the surface, hugging the ground around the lake and causing 1,700 people to be suffocated.

But around Lake Kivu, where about two million people live (250,000 of them in Goma alone), the results could be far more devastating.

Around 350 times as much gas as was found in Lake Nyos is stored below the surface in Lake Kivu, in part as a result of the eruption of Mount Nyiragongo near Goma in 2002.

Prof George Kling from Michigan University told the scientific journal Nature that Kivu was "basically the nasty big brother of Nyos."

He added that the Cameroonian disaster was because Lake Nyos "was essentially like a bottle of beer that had been shaken up.

"When you opened it, carbon dioxide bubbled up and the beer frothed over. A glassful is OK. A lakeful is deadly."

The Observer newspaper reported that studies by the Swiss Federal Institute of Aquatic Science had found a nearly 20 per cent increase in methane concentration in Lake Kivu between 1974 and 2004 and that carbon dioxide levels had also increased by around 10 per cent in that 30 year period.

It also said that plankton fossils found on the lake's bed "have revealed several massive bouts of biological extinctions in Kivu over thousands of years."

The scientists are however unable to say whether a new disaster is imminent.

What has made the issue more topical however is the attempt by engineers to tap Lake Kivu's supplies of methane through piping out the gas from floating platforms.

If successful, the gas could then be burnt and used as a source of industrial and domestic energy.

Scientists, however, are uncertain of the effect of the piping attempt.

Some believe that, over time, tapping Kivu's methane could, theoretically, reduce a risk of the eruption of the gas.

Others however warn that tampering with the lake's gases could actually increase the chances of triggering a disaster.