Villagers in Cameroon woke in the night struggling to breathe, with no fire and no smoke on the horizon. What had reached them from the lake next door?
that had been collecting for years. Lake Nyos looks like an ordinary lake from the surface, and on its floor carbon dioxide from a geological source had accumulated over years. On one night in 1986 a large part of the gas came out at once. The heavy cloud flowed down the valleys and replaced the air that people and animals were breathing. According to the official geological report, at least 1,700 people died.
In deep, pressurized water a gas can stay dissolved for a long time. At Lake Nyos that situation allowed an unusual accumulation of carbon dioxide.
When the water released the gas, it moved close to the ground and reached settlements in the valleys. The geological report sets out the mechanism of accumulation and asphyxiation, and the account of the event that began the release is not closed down to the last detail.
The condition that allowed the disaster was built over long years. The lake is : deep, tropical, and its layers do not mix seasonally. Beneath it runs through which carbon dioxide rises from a deep source, dissolving and gathering in the bottom water with no way out.
What makes a reservoir like that dangerous is that feeds on itself: once deep water is lifted, the pressure on it falls, the gas leaves solution and pushes more water upward. Once the cloud was out, being decided the rest: it flowed down the slopes and filled inhabited valleys, killing by replacing the oxygen. The international team that investigated the event established the source of the gas with chemical and isotopic tests, while the precise trigger of that night remains an open question.
wat. Lake Nyos stored carbon dioxide in its depths, and then released a cloud that flowed into the villages below it.
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Some lakes can store an invisible danger beneath the surface of the water.
How do we know?
A USGS investigation after the disaster, gas measurements in the lake water, and documentation of how the cloud spread through the nearby valleys.
What is still unknown
The precise details of the trigger for the release are still less certain than the fact that the gas came out.
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Where to next
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