#64 Science in History
21st August 1986
Exploding Lake
On this day in 1986 Lake Nyos, a crater lake located in Cameroon, West Africa, released a silent killer that ended the lives of over 1700 people as well as innumerable animals.
Lake Nyos sits atop a volcanic vent. Over time, carbon dioxide gas accumulated in the deep layers of the water due to volcanic activity and bacterial decomposition of organic material. With limited movement in the water, the carbon dioxide remained dissolved in the colder depths of the 200-metre-deep lake, with this cold-water layer ‘capped’ by less dense warmer water.
Lakes that exhibit such potentially dangerous behaviour are termed limnically active lakes or exploding lakes. A limnic eruption, often referred to as a lake overturn, is an exceptionally rare natural catastrophe characterized by the abrupt release of dissolved carbon dioxide from the depths of a lake. This sudden release forms a noxious gas cloud that can lead to the suffocation of wildlife, livestock, and humans in the vicinity.
Scientists believe that a disturbance, possibly a landslide, caused the lake's layers to mix, which disrupted the stratification that had kept the gas contained. This triggered a rapid and violent release of an estimated 1.6 million tons of carbon dioxide gas. The released gas formed a dense cloud that hugged the ground and flowed down nearby valleys for 15 miles, displacing the air, and leading to asphyxiation for those caught in its path.
In the aftermath of the disaster, various efforts were undertaken to prevent a similar event from occurring again. One approach involved the installation of degassing systems in the lake to gradually release the trapped carbon dioxide in a controlled manner. These systems involve pumping water from the bottom of the lake to the surface, allowing the gas to escape harmlessly into the atmosphere.
The Lake Nyos incident in 1986 is perhaps the most well-known and extensively studied limnic eruption, primarily due to its devastating consequences and the attention it brought. However, there have been a few other documented cases of limnic eruptions or similar events causing deaths before this incident. There were, in fact, reports of smaller releases of carbon dioxide from Lake Nyos before the 1986 disaster. These earlier events did not cause significant harm, but they did provide some warning signs of the potential danger posed by the lake's gas build-up.
Just two years before the Lake Nyos event, another limnic eruption occurred at Lake Monoun, located not far from Lake Nyos. On August 15, 1984, a sudden release of carbon dioxide from Lake Monoun resulted in the deaths of 37 people. The event was similar to the Lake Nyos incident but on a smaller scale.
The Lake Nyos incident, however, remains the most catastrophic and well-documented example of a limnic eruption causing significant loss of life. It was a turning point in understanding the mechanisms behind these events and in the development of strategies to prevent or mitigate their impacts.
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