Mystery of Lake Nyos

 On 21 August 1986, a limnic eruption at Lake Nyos in northwestern Cameroon killed 1,746 people and 3,500 livestock.^[1]

The eruption triggered the sudden release of about 100,000–300,000 tons (1.6 million tons, according to some sources) of carbon dioxide (CO₂). The gas cloud initially rose at nearly 100 kilometres per hour (62 mph; 28 m/s) and then, being heavier than air, descended onto nearby villages, displacing all the air and suffocating people and livestock within 25 kilometres (16 mi) of the lake.

A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in the waters and therefore the risk of further eruptions.

It is a possibility that other volcanic gases were released along with the CO2, as some survivors reported a smell of gunpowder or rotten eggs which indicates that sulfur dioxide and hydrogen sulfide were present at concentrations above their odour thresholds. However, CO2 was the only gas detected in samples of lake water, suggesting that this was the predominant gas released and as such the main cause of the incident

Eruption and gas release

What triggered the catastrophic outgassing is not known. Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake. A third possibility is that cool rainwater falling on one side of the lake triggered the overturn. Others still believe there was a small earthquake, but because witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely. The event resulted in the supersaturated deep water rapidly mixing with the upper layers of the lake, where the reduced pressure allowed the stored CO2 to effervesce out of solution