Imagine wandering into a village and everything motionless. Just a mound of lifeless bodies lying around, leaving you horrified. Such a terrible scene would qualify for horror movie but this is exactly what happened in the villages around Lake Nyos in Cameroon in 1986, where more than 1,700 people instantly died from asphyxiation after inhaling huge quantities of carbon dioxide emitted from the lake.
Such terrible natural disasters are rare that only two have ever been recorded, once in 1984 from Lake Monoun and the other in Lake Nyos but now an even greater danger lies dormant. Lake Kivu, which is much bigger and shared by Rwanda and the Democratic Republic of Congo, and situated in a more densely populated region could potentially be the source of a devastating calamity.
Lake Kivu is among three of rare water bodies in the world known as limnic lakes . Lakes such as these have the property of erupting massive amounts of carbon dioxide, a phenomenon known as a lake overturn. An event that could be triggered by various catalysts such as an eruption, or earthquake if the saturation of the carbon dioxide contained within the lake reaches critical levels of 100 percent. To illustrate this in layman terms, prior to a lake being saturated, it behaves like an unopened carbonated beverage (soft drink) : the carbon dioxide is dissolved in the water similarly to how it is dissolved in the lake. In both the lake and the soft drink, carbon dioxide dissolves much more at high pressure. When the drink is open, the pressure is released thus making the carbon dioxide come out of solution. If the lake reaches full saturation, the pressure exerted by the gases will be more than the pressure caused by the lake thus making it highly unstable and a trigger is all that is required to set off an eruption sending vast amounts of carbon dioxide to bubble out of the lake.
Fortunately, the chances of such an event transpiring are not high. “The risks are a little bit above 50 percent given the saturation levels of the gas in the lake,” says Augusta Umutoni, Engineer in charge of environmental concern in the Lake Kivu project.
“The pressure exerted by the gas contained in the lake needs to be more than the hydrostatic pressure of the water,” she adds. This is something that is not likely to occur due to the recent methane gas extraction that is being extracted. Umutoni says that CH4 (methane) has a big partial pressure, if extracted and this significantly reduces the overall pressure exerted by both gases. The extraction of methane gas not only acts as source of vast amounts of energy but it also increases the stability of the lake.
“The lake produces more gas and recharges itself at a rate of 150 million cubic metres per year ; this would take about 100 years for it to reach critical saturation levels of 100 percent. Presently, we are still on 57 percent level of saturation, she says, adding that this diminish the danger.
Umutoni points out that Lake Kivu is situated in a region of high seismic and volcanic activity. It is even close to Mount Nyiragongo , which erupted in 2002. The eruption caused lava to cover a big portion of Goma city and this streamed down to Lake Kivu. “At the time, there was fear that the lava would cause gas saturated waters to rise to the surface. Luckily, this did not happen,” she says.
“After the explosion, the European Union sent an expedition of experts to investigate on this and it was discovered that the lava had sunk to a depth of around 100 meters beneath the lake, where the main gradient of the gas is at 260 metres. This indicates that a seismic wave that would only be able to make lava reach at that point and trigger a lake overturn would have to be one of monumental magnitude.” observes Augusta, something that is unlikely to occur.
She says that this improbability should not be taken for granted, because there is another area of Lake Kivu , known as Kibuno Bay that contains 100 percent saturation levels of carbon dioxide. The discovery of this has prompted the establishment of a de-gasing plant to reduce the risks. However, she says that installation and implementation of this project is far from being underway.
Umutoni observes that Lake Kivu seems to be as fascinating as much as it is potentially hazardous. “Nevertheless, it would be safe to assume that the dangers lying around the lake despite their great disastrous potential have low probability of occurrence. The methane gas project for now is an excellent way to avert this danger in the long term by not only providing greater socio-economic benefit but by also maintaining and perhaps increasing the stability of this great lake,” she recaps.
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