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Researchers try to defuse African time bomb

Lake Kivu, pictured from the Rwandan side

Swiss scientists are helping the government of Rwanda to extract potentially lethal methane from a dangerous lake for much needed electricity production.

The threat in the Lake Kivu area comes from billions of cubic metres of gas dissolved deep underwater that could kill large numbers of people if it were to escape.

The aim of the Rwandan government project is to extract methane from the lake, which straddles the border with the Democratic Republic of Congo, to ensure secure power supplies in the region for decades. The authorities also want to reduce the risk of a deadly gas eruption.

"The government of Rwanda has issued the first concessions for extracting methane from Lake Kivu," scientist Martin Schmid told swissinfo.

Schmid, who works for the Swiss Federal Institute of Aquatic Science and Technology at Dübendorf near Zurich, said that the researchers were advising the contractors and the government on how to minimise the impact of the extraction process.

At present, the gas remains dissolved deep underwater as a result of high pressure and the extremely stable water layers of the lake, which limits exchanges between the bottom and surface zones.

But if gas concentrations continue to increase or if a severe disruption happened - following a volcanic eruption or a major earthquake - large quantities of gas bubbles could rise to the surface, possibly triggering a massive gas eruption.

The release of a mixture of carbon dioxide and methane gas could have catastrophic consequences on the densely populated shores of the lake where about two million people live. Hundreds of thousands could be asphyxiated.

In 1986, about 1,800 people died this way after carbon dioxide burst from Cameroon's Lake Nyos. "Killer lakes" sparked global headlines.

Nutrient cycle

The institute is currently investigating the nutrient cycle of the lake. This is important because the methane is biogenic, which means it is produced from decomposing dead algae on the bottom of the lake.

"It's important to understand the cycling in the lake to see how the methane is produced and why it's been increasing lately," Schmid explained.

He said at present the lake was in principle "very stable" and it would need a huge earthquake or magma input directly in the bottom of the lake to trigger a gas eruption.

However, extracting the methane is not without risks.

"One thing that is important is to maintain the stable stratification of the lake because otherwise the gases could rise near the surface and this would increase the risk of catastrophic eruption," Schmid said.

Harnessing the lake in this way could be important for the future of Rwanda, where it is a problem to produce enough electricity and energy prices are quite high.

"If the methane is removed from the lake in a controlled way, this is a first step in making the lake less dangerous," Schmid added.

swissinfo, Robert Brookes

Methane extraction

When a pipe extending into the depths of the lake is installed, water rises up through it spontaneously as a result of the gas bubbles forming in the pipe.

At the surface, the water bubbles like carbonated water from a bottle that has been shaken before being opened.

The methane then has to be separated from the carbon dioxide before it can be used.

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Lake Kivu

The lake lies almost 1,500 metres above sea level. It covers an area of 2,400 square kilometres and has a maximum depth of 500 metres.

Worldwide, only two other lakes are known to harbour similar quantities of gases – Lakes Monoun and Nyos in Cameroon.

In both of these cases, however, carbon dioxide predominates.

The methane in Lake Kivu is produced by the decomposition of dead organic matter (algae) at the bottom.

Experts estimate the value of Lake Kivu's gas reserves to be around SFr16 billion ($13.5 billion).

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