Volcanic Hazards: Gases
Gases are 1 to 5% of magma by weight, and mainly consists of water vapor and CO2
Lake Nyos, Cameroon
- Last eruption: 1984 - 1986
- Elevation: 3,579' (1,091 m)
- Type: Maar A volcanic crater that is produced by an explosion in an area of low relief, is generally more or less circular, and often contains a lake, pond, or marsh.
August, 1984 eruption: smaller gas burst from nearby Lake Monoun, where 37 people killed as a result.
August, 1986 eruption: Lake Nyos erupted 1 km of CO2. Over 1700 people were killed up to 26 km away from the lake. It was not clear initially how these people and animals died. People reported entering villages only to find the occupants slumped over their food or lying on the ground as if they were passed out. Subsequent study of the area revealed that they died of carbon dioxide poisoning.
So, what happened? Gases can be released from the volcano either during an eruption or through cracks and fissures in the ground. This is what happened at Lake Nyos (see image below). Gas is released via fissures in the ground - although in this case they exit into a lake instead of the atmosphere. The water at the bottom of the lake is cold and dense, trapping the gas at the bottom. The gas builds up over time until something happens to disturb the water above it. The gas bubbles up to the surface and spreads outwards over the land.
Only three lakes in the world are known to contain high concentrations of dissolved gas in their bottom waters: Lakes Nyos and Monoun in Cameroon and Lake Kivu in East Africa. Only Lakes Nyos and Monoun are known to have recently released gas resulting in the loss of human life.
Scientists are now monitoring Lake Nyos to ensure that a similar event doesn't happen again. The lake is being degassed - gas is being released in a controlled fashion so it does not build up again.