The Lake That Killed Everything

On August 21,1986 more than 1700 people and some 3500 livestock were found dead next to Lake Nyos in Cameroon. Any living thing within 25km radius of the lake was killed and the mysterious incident brought with it many tales of folklore. Some said an evil spirit had emerged and taken the lives of all those who lived near the lake. That was until scientists discovered that the deaths were related to carbon dioxide (CO2) poisoning. Lake Nyos was formed in a volcanic crater and became a high pressure storage unit of CO2 beneath the water. The CO2 eventually became so pressurized that it exploded creating a burst of water into the air and causing what scientifically known as a limnic eruption.

 A limnic eruption is said to be "a rare type of natural disaster in which dissolved carbon dioxide suddenly erupts from deep lake waters, forming a gas cloud capable of suffocating wildlife, livestock, and humans." Also known as a lake overturn, it can happen quickly, unexpectedly, and with severe consequences to any living things in the surrounding area. Certain factors need to be in place for a limnic eruption to occur. It is thought that these eruptions are generally triggered by seismic activity. Disruptions in the Earth's crust can cause underground shifts, triggering the explosions or releasing pressure in the area. This phenomenon, in turn, is thought to lead to the initial disruption that causes the eruption.

 Earthquakes, volcanic activity, and other explosions can cause these triggers. Eruptions do not occur in all lakes, however, the lake has to be already limnically active. It means it contains water that is high in carbon dioxide. The lake must also have a cool lake bottom, as this indicates that the water in the lake does not have direct connections to a volcano. Direct volcanic interaction would have different results- such as a geyser reaction - and would not become limnic. A limnic lake must also have an upper and lower thermal layer with different carbon dioxide saturation. The sudden mixing of these layers causes the explosion, and the lake must be in proximity (but not directly connected to) seismic or volcanic activity. 

Limnic lake environments occur in waters where there is an extremely high level of carbon dioxide. Higher levels of carbon dioxide can be dissolved in water in areas of high pressure. Because of this, deep lakes can contain extreme levels of carbon dioxide in the lake bottom (and have lower levels towards the surface). It is also true in colder water, which again tends to be at the lake's bottom. The carbon dioxide itself is usually from decomposed plant or animal matter on the lake's floor. In these conditions, the lake is stable, but also on the verge of eruption at any time - much like an unopened can of carbonated liquid is stable, but will fizz once open and the pressure released. In the same way, a rise in temperature or a change in pressure can cause the carbon dioxide within the lake to be expelled from the water - usually quickly and violently.

Limnic eruptions are quick, unexpected, and very deadly. Initially, carbon dioxide explodes out of the lake - much like a shaken-up can of carbonated liquid would once it is opened. Then, the dense carbon dioxide cloud forms over the lake and surrounding area. This gas is heavier than air, meaning it is a low-hanging cloud that settles along the Earth's surface. This gas cloud, due to its density, displaces lighter air. In essence, this means that the carbon dioxide cloud pushes out breathable air and removes oxygen from the areas affected by the cloud. Two major reactions occur in humans and other animals - they are unable to gain oxygen from the air, and they begin to suffocate, and/or the carbon dioxide poisons the body by causing natural body fluids to become too acidic.

 An estimated 80 million cubic meters of carbon dioxide were expelled in Lake Nyos explosion, which asphyxiated much of the surrounding town, preventing them from getting any oxygen. But Lake Nyos is not the only such lake. There is a Lake Kivu which is located between Rwanda and the democratic Republic of the Congo. It is 1500 times larger than Lake Nyos. This lake is a tourist attraction but its also a ticking time bomb due to both CO2 and Methane gas built up underneath. And experts say it could threaten millions living in the region. Engineers built a floating gas plant on the lake to monitor the situation and release the natural gasses to produce electricity. It covers 30% of Rwanda's electricity needs. But researchers are in disagreement over which gas extraction method is correct? Such efforts might disturb the lake and actually cause more danger instead of overcoming it.