Deadly Lakes

WHAT ARE LIMNIC ERUPTIONS?

- Gina Hagler

It's one of the rarest forms of volcanic activity-and among the most lethal. A limnic eruption occurs when a dangerous gas trapped at the bottom of a volcanic lake suddenly turns over and then escapes. This gas, carbon dioxide, is heavier than air. It's also colorless, odorless, and impossible to breathe. One limnic eruption at Lake Nyos in Cameroon, Africa, in August 1986 asphyxiated 1,700 people and 3,500 livestock overnight. This event alerted scientists to the threat and led them on a campaign to study and stop these killer lakes before history repeats itself.

Conditions for a Limnic Eruption

These unusual but deadly explosions fall into the category of natural disasters. Limnic eruptions are rare because the conditions for their formation must be precise. There must be a buildup of carbon dioxide (CO2) in solution in the cool waters at the bottom of a body of water-but not just any body of water. The water must be fresh water, not salt. The water must be very deep and still. Because this is essential to a limnic event, the body of water is often in the form of a crater lake-one that has been created by volcanic activity beneath the surface of the Earth.

It is not enough to have a deep body of fresh water with a low salt content. There must also be a source of carbon dioxide. The carbon dioxide usually enters the lake from the bottom, in the form of gas from an underwater volcano. As more and more CO2 enters, the water becomes saturated with the gas. There is a limit to how much CO2 the water can hold while still remaining stable. As the limit is reached, conditions are ripe for a limnic eruption.