Lake Kivu, Lake Monoun, and Lake Nyos might sound just like any other ordinary lakes but they are actually three of the most dangerous lakes in the world. Situated in the boarder of Rwanda and Democratic Republic of Congo and Cameroon in South Africa, the latter two, have caused some of the worst natural disasters in the 1980’s. These events killed almost 1900 people, 3500 livestock, and many wildlife in the surrounding villages and towns.
Carbon dioxide resulting from the close association with volcanic activities is the reason why the lakes are so deadly.
Imagine a fizzy drink bottle being as big as 132 million m3. It contains A LOT of gas and is under a lot of pressure. This is what it’s like deep down at the bottom of the lakes. The water is saturated with dissolved gas –carbon dioxide. The high pressure exerted by water at great depths keeps all the gases inside. As pressure increases, more gas is dissolved in the lake. However, if the pressure was removed, all the gases will start bubbling out.
Diet coke explosion (source wikimedia commons)
That is a disaster and not just any ordinary disaster, it is a limnic eruption. Limnic eruption is a rare natural phenomenon, where a large amount of carbon dioxide gas is released from a deep lake, also known as lake overturn.
The limnic eruptions in Lake Monoun and Lake Nyos were resulted from landslides and phreatic explosions respectively. The eruptions caused large clouds of carbon dioxide to be released above the lake and expanded into the surroundings. Since carbon dioxide is heavier than air, it can displace oxygen and fill the area with unbreathable air. Consequently, people and animals died from carbon dioxide poisoning and severe oxygen deficiency called asphyxiation.
The picture below describes what happened in Lake Nyos in the 1986 limnic eruptions.
Lake Kivu differs from the other exploding lakes and contains large amount of methane in its water column – 55 billion m3 and still increasing. Methane is highly explosive and could trigger further release of carbon dioxide once ignited. Scientists suspected that Lake Kivu could contain 1000 times more gas than Lake Nyos and Lake Monoun. Hence, the consequences of limnic eruptions in Lake Kivu could be catastrophic and especially dangerous to the two million people living around the lake.
Another lethal outcome of limnic eruption is the occurrence of tsunami caused by the displacement of water in the lake due to the escaping gas. The tsunami wave in the 1986 limnic eruptions in Lake Nyos was recorded to reach 20 metres in height.
At the moment, in order to prevent further disastrous events, a pipe has been inserted into Lake Nyos . The carbon dioxide at the bottom of the lake is slowly released via the pipe, which reduces the build-up of gases in the lake. Similar project has been suggested to implement at Lake Kivu called KivuWatt. However, instead of carbon dioxide, the methane is extracted as an energy source to provide electricity to the people living near the lake.
Here is a youtube clip of dry ice bubbles which resembles the build-up of carbon dioxide in the lake and exploded. Note that all the gas escaped and sank to the bottom, which was how the gas expanded to the nearby villages and towns in the 1980’s limnic eruptions.