Lake nyos

Tectonic Event Case Study- WJEC AS G1

1. Lake Nyos Was it a volcanic eruption?

2. 21 st August 1986 When did it occur?

3. Its situated in Northwest Cameroon, around 30 miles from the Nigerian border to the north. The most affected villages of this disaster were Cha , Nyos, and Subum . Where is it located?

4. It was a limnic eruption which is a lake overturn , and a rare type of natural disaster in which dissolved carbon dioxide ( CO₂) suddenly erupts from deep lake water, suffocating wildlife, livestock and humans . The turning over of the lakes is a natural process and most lakes do this twice a year, but the reason that this was so deadly was because instead of it happening gradually, it happened suddenly and quickly and so large amounts of CO₂ were released. What type of eruption was it?

5. A 100 m fountain of water and foam formed at the surface of the lake. The huge amount of water rising suddenly caused a wave of at least 25 metres A large cloud of CO₂ was then emitted from the lake, of around 100,000-300,000 tons. This travelled down the side of the hill and into nearby villages. Once it reached this village it caused many of the inhabitants to die from asphyxiation during their sleep. What happened?

6. The blue waters of the lake turned a rusty colour after the cloud of gas due to iron rich water after being oxidised by the air The lake’s water level dropped by about 1m and the trees surrounding the lake fell down. What happened afterwards?

7. One camp believed a volcanic eruption released CO₂ and blew up the lake. Another camp thought CO₂ was gradually leaking into and being stored in the lake, and a landslide then displaced this gas The main theory that is believed by most is the latter. The CO₂ leaking into this lake is thought to be coming from a pocket of magma within the extinct volcano, which lies at the bottom of the lake. Why did it happen?

8. The immediate effects were that around 1700 people suffocated from a large cloud of CO₂. With around 3500 livestock being killed as well. Shortly afterwards around 4000 inhabitants fled the surrounding areas with many of them later developing respiratory problems because of the gases. Who was affected?

9. After this disaster, scientists started to think of ways to first degas the lake and then of how to avert future disasters. French scientists came up with the idea of putting in pipes to control the amount of CO₂ released. This would not stop the problem but it would allow scientists to control when it was going to be released, as well as the amount being released. They also plan to reinforce the lake’s walls, as they are becoming increasingly weaker. If these were to give way the gas from the bottom of the lake would be released and it would cause another disaster. What is being done to prevent this happening again?

10. The degassing will firstly take place with scientists controlling the release, but the plan in the future is for it to become self sustained.