Engineers aboard a floating power station on Lake Kivu could only watch nervously as a volcano in the distance erupted violently, sending tremors rumbling through the water beneath them.
However, it was not the lava shooting from Mount Nyiragongo in May last year that spooked them, but the enormous concentrations of potentially explosive gases within Kivu, one of Africa’s great Rift lakes lying between Rwanda and the Democratic Republic of the Congo (DR Congo).
Flanked by rolling green hills tumbling into glassy waters, Kivu is not quite the picture of tranquility it seems, said Francois Darchambeau from KivuWatt, a company that extracts gas from the lake’s waters for electricity.
Thousands of years of volcanic activity has caused a massive accumulation of methane and carbon dioxide to dissolve in the depths of Kivu — enough to prove monumentally destructive in the rare event they were released.
If triggered, a so-called limnic eruption would cause “a huge explosion of gas from deep waters to the surface” resulting in large waves and a poisonous gas cloud that would put the lives of millions at risk, said Darchambeau, environmental manager at KivuWatt.
“This is what we call a killer lake,” said the limnologist, or an expert in freshwater systems.
Only three such lakes exist in the world: Kivu, and Nyos and Monoun in northwest Cameroon.
The latter two had limnic eruptions in the 1980s, and the bigger disaster at Nyos suffocated more than 1,700 people in a release of carbon dioxide.
However, these catastrophes occurred in a rural area, whereas about 2 million people would be “at risk” of such a similar disaster involving Kivu, Darchambeau said.
In Rwanda and DR Congo, many live in fear of the lake’s harmful potential, and stories abound of swimmers disappearing into its depths after being asphyxiated or pulled under.
However, the lake poses both peril and promise.
KivuWatt, which says this is the only project of its kind anywhere in the world, saw an opportunity to tap the abundant gases for energy generation.
A 20-minute speedboat ride is required to reach KivuWatt’s unique floating platform, a compact tangle of pipes and buoys as high as a multistory building moored in the Rwandan part of Kivu.
With a deafening roar, the facility pumps water saturated with carbon dioxide and methane from about 350m to the surface.
As it rises, the water and gas separate as the pressure changes.
“It is like opening a bottle of soda,” said KivuWatt director Priysham Nundah, who described the project as “halfway between a thermal and a renewable energy plant.”
The extracted methane is sent through a pipeline to a second facility onshore in Rwanda, where the gas is used to generate electricity.
The carbon dioxide is pumped back into the lake at a precise enough depth to ensure the delicate balance is not upset.
The company says it hopes that removing methane could reduce pressure within the lake, possibly lowering the risk of a limnic eruption.
However, fears of such a disaster were reawakened when Nyiragongo — a volcano north of Kivu in DR Congo — roared to life early last year.
Lava flows killed 32 people and destroyed hundreds of homes as earthquakes shook the region.
One lava flow pushed deep into the earth under the lake itself.
From their station, KivuWatt’s engineers watched the sky turn red and angry.
“It was very frightening,” Nundah said. “When the rates of earthquakes and the frequency of earthquakes started to rise … no one could really say what would happen.”
A shutdown was considered, but the engineers held their nerve.
Suspending operations would have serious consequences for Rwanda, as KivuWatt produces about 30 percent of the annual electricity in the east African nation.
US company ContourGlobal, which owns KivuWatt, launched the Lake Kivu venture in 2015 and for a time considered expanding its capacity from 26 to 100 megawatts.
Another company is exploring the possibility of launching its own 56 megawatt gas extraction venture on the lake.
There are no plans in the short term for such a project on the Congolese side.
How long it will take to deplete these vast gas reserves will depend on the pace of extraction, said Martin Schmid, a researcher at the Swiss Institute for Water and Environmental Research.
“Just with KivuWatt alone it will take, I don’t know, centuries to have really a reduction of methane in the lake,” Schmid said.
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