Limnic eruption
A rare disaster in which carbon dioxide dissolved in a deep lake suddenly bursts out, smothering the surrounding land in heavy gas.
A limnic eruption is the sudden release of a huge amount of dissolved carbon dioxide from the deep water of a lake. It depends on Henry's law: the amount of a gas that dissolves in a liquid is proportional to the pressure of that gas above it, and cold water generally holds more gas than warm.
In a few deep crater lakes, volcanic carbon dioxide seeps in from below. The cold, high-pressure bottom water can hold a great deal of it, and the lake's layers stay unmixed, so the gas builds up for years. If something disturbs the layers, deep water starts to rise. As it rises the pressure on it falls, gas comes out of solution as bubbles, the bubbly water rises faster and releases more gas: a runaway process, like shaking a bottle of fizzy drink and opening it.
On 21 August 1986 Lake Nyos in Cameroon released an estimated 100,000 to 300,000 tonnes of carbon dioxide. Because the gas is heavier than air, it flowed down the valleys like an invisible flood, suffocating 1,746 people and about 3,500 livestock up to 25 kilometres away. Two years earlier, a smaller eruption at nearby Lake Monoun had also been deadly. These are the only two limnic eruptions recorded in modern history.
Since 2001, pipes have carried deep water up from the bottom of Lake Nyos, letting the gas escape safely, a little at a time.
Coming up in future stories
- The Lake That Suffocated a Valley 1986 · Lake Nyos, Cameroon