Picture this; You find yourself at a remote point in Africa, thirsty and dog tired. Cresting a ridge, you see stretching out below you an idyllic, albeit dark, lake. The ridge you are standing on runs around the lake. The steep sides go down to a flat area beside this clean, fresh water. It’s getting late so you make your way down and after refreshing in the cool water you pitch camp at the ridge base and eat dinner by campfire looking out over your private vista.
It sounds tempting doesn’t it? Well, it may not be the smartest move. Lakes which fit this description (there are three – Lake Nyos and Lake Monoun in Cameroon, and Lake Kivu in Rwanda) can, and do, kill. The most recent example of this was Lake Nyos, Cameroon where approximately 1700 people died. These lakes became topical once more when the fossil of Ida was uncovered and the theory is that such a lake was this creature’s downfall.
Lake Nyos, Cameroon, Gas Release August 21, 1986. Dead cattle and surrounding compounds in Nyos village. September 3, 1986. Thanks to USGS for the image.
These lakes are created by volcanic activity which superheats surface water. The resultant steam causes rocks to expand and a series of explosions follow leaving a massive crater. Eventually this fills with water to a great depth.
Due to the volcanic nature of its creation these lakes sit on carbon dioxide exhausts. The depth of the lake is now an issue. The huge pressures compress the would-be escaping gases which then sit on the lake floor, constantly growing and becoming concentrated.
In the case of Nyos, the cause of the eventual fatal release remains unknown. It was likely to have been a large movement of a geological nature, either heating or a sub-surface landslide or eruption. Whatever happened the gas was released and the results were grave.
1.6 million tonnes of carbon dioxide was released; this cloud rose at nearly 100 kilometres (62 mi) per hour. Being heavier than air the gas filled the valleys below the ridges displacing all the air and suffocating some 1,700 people within 25 kilometres (16 mi) of the lake, mostly rural villagers, as well as 3,500 livestock. The movement was so sudden an amount of water rising caused a wave of at least 80 feet that scoured the shore of one side.
Joseph Nkwain survived the event and had a tragic story of loss; “I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible. I heard my daughter snoring in a terrible way, very abnormal. I collapsed and fell. I was there till nine o’clock in the morning. A friend of mine came and knocked at my door. I was surprised to see that my trousers were red, had some stains like honey. I saw some starchy mess on my body. My arms had some wounds. I didn’t really know how I got these wounds. I wanted to speak, my breath would not come out. My daughter was already dead. I went into my daughter’s bed, thinking that she was still sleeping. I slept till it was 4:30 p.m. in the afternoon. I managed to go over to my neighbors’ houses. They were all dead. I got my motorcycle and as I rode through Nyos I didn’t see any sign of any living thing. I was unable to walk, even to talk, my body was completely weak.”
Two weeks after the disaster and the lake looks calm
Following the disaster, doctors in Yaoundé found that many people, although not killed, had been partially poisoned by the gases. Symptoms described included burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled.
Since the tragedy the carbon dioxide has been building up again just as before. A joint effort with French scientists has setup what is basically a huge straw to allow the gases to safely be exhausted.
Bibliography
San Diego State University Report
The world’s least reliable encyclopaedia
Arizona University’s Geology Department
How Stuff Works – a bit more in-depth
This article was posted on
Wednesday, May 27th, 2009 at
18:22.
It is archived in Wild Places and tagged Africa, disaster, gas, geology, water.
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