THE LAKE NYOS DISASTER, 1986

By Holly Goodrick

In August 1986 at Lake Nyos in Cameroon, West Africa, a limnic eruption occurred. A cloud rich in carbon dioxide and water droplets rose at 100km per hour from the floor of the lake without warning. The onlookers would have seen a fountain of water shoot up 90m into the air. Carbon dioxide is 1.5 times the density of air so the cloud stayed near to the ground and swallowed up villages. At a distance of 23km from the lake the air had a high concentration of carbon dioxide from the eruption. As a result, in the surrounding 4 villages, the inhabitants were killed almost instantly. This occurred because at a high concentration, carbon dioxide displaces oxygen so there was a lack of oxygen in the air and they died of asphyxiation. However, they didn’t die in trauma but most died in their sleep. At 10% carbon dioxide concentration people typically hyperventilate, become faint and fall into a coma and at 30% they die. The cloud killed 1746 people and 3500 livestock within minutes.

Lake Nyos is formed on top of a volcanic source, which releases carbon dioxide amongst other gases. The gas does not escape to the atmosphere but dissolves at the bottom of the lake. Due to the lake being 200m deep, there is an extremely high pressure at the bottom of the lake, allowing the carbon dioxide to dissolve more readily. Scientists have estimated that at the depth of 200m, water holds 15 times its own volume in carbon dioxide.   As one can imagine, this led to vast quantities of gas at the bottom of Lake Nyos.

The locals thought that the disaster was caused by the anger of the spirit women living in the lake; however, scientists are not certain but, unlike similar disasters, they do not believe that the limnic eruption was triggered by a landslide or earthquake but by a large mass of rainwater in the air above the lake. To make matter worse, the August winds would have blown the rainwater to one side of the lake. Because rainwater would have been denser than the warm water in the lake, the rainwater would have sunk down on one side of the lake and displaced the water at the bottom containing the large volume of carbon dioxide. As this water rose, it would have experienced less pressure and the dissolved carbon dioxide would have come out of the solution and bubbled upwards rapidly. The bubbles would have lowered the overall density of the mixture in the lake so the carbon dioxide would be released in greater quantity and rise faster. This would result in a sudden, violent expulsion of carbon dioxide from the lake. It has been calculated that so much gas escaped that the surface level of the whole lake decreased by 1m. The cloud would have travelled down the slopes at 20-50km per hour and engulfed the surrounding houses.

In order to prevent a future crisis, in 2001 engineers installed pipes, which suck the carbon dioxide in the lakebed and gradually release it into the air. Disasters such as these not only help to progress people’s knowledge and understanding, but also help us to realise the power of the natural world.