How Gas Build-Up at Lake Nyos Killed More Than 1,000 People

One of the CO2 vents at Lake Nyos

Lake Nyos is a crater lake in northwestern Cameroon. It is one of only three lakes in the world known to be capable of causing a very unique sort of natural disaster. Lake Monoun, which is 60 miles to the southeast of Nyos and Lake Kivi on the Congo/Rwanda border are the other two, but neither of them has been as deadly as Lake Nyos. On August 26, 1986, 1,700 people in the vicinity of the lake died mysteriously. Animals in the area were also found dead. There were no signs of trauma or disease. It appeared as if these people just fell down where they stood and died. Some were even still asleep in their beds.

After the disaster, scientists turned to Lake Nyos for answers. It was noticed that the normally deep blue lake had turned a reddish brown color. This color lead scientists to suspect that the iron at the bottom of the lake had somehow made its way to the top, where it oxidized and temporarily changed that lake’s color. When the lake was studied, abnormal amounts of carbon dioxide were found at the bottom of the lake. This would lead them to the answer that they were looking for.

Two years before the Lake Nyos Disaster, a similar event had occurred at Lake Monoun. Thirty-seven people had lost their lives when they suffocated on CO2 that suddenly escaped from the lake. Apparently the same thing had happened at Nyos, but on a much larger scale.

There is an extremely large amount of carbon dioxide at the bottom of Lake Nyos because the lake does not naturally “turn over” frequently, the way most lakes do. The carbon dioxide enters the lake naturally and because the lake is very deep, the upper waters of the lake hold down the carbon dioxide. The waters are also unusually calm, and the lack of movement keeps the carbon dioxide at the bottom of the lake as well. When something does naturally occur to cause some of the lake’s water to turn over, the result is a massive release of the built up gas.

On the day of the Lake Nyos disaster, something occurred (scientists aren’t sure exactly what, but several good theories exist) that made the CO2 rise rapidly out of the lake, causing the lake to bubble tremendously and spray water into the air. Because CO2 is heavier than air, it didn’t disperse. It sank down into the valleys surrounding the lake in a cloud that is estimated to have been roughly 328 ft. tall. The cloud moved through the area at speeds between 12.42 and 31.06 miles per hour. The average running speed for a human is roughly 12 miles per hour. It is unlikely that anyone would have been able to outrun it, even if they had noticed that something invisible and deadly was moving toward them.

The cloud killed nearly every human and animal within a 15-mile radius of the lake. Because the carbon dioxide was in concentrations higher than 10%, it caused everything in the area that breathes to become asphyxiated. There were very few survivors. Some people that were high enough above the lake survived, others simply woke up two days later, after the cloud had dispersed. Some people, who were lucky enough to be inside their homes with the doors and windows closed, survived as well.

The carbon dioxide in Lake Nyos began building up again immediately after the disaster. It was soon realized that another disaster would be inevitable if nothing was done to prevent it. So, scientists developed a pump with a long pipe going to the bottom of the lake, which brings the gas to the surface. The pipe then empties out above the water line with a harmless spray of water and gas. At this time, there are not enough pumps on the lake to prevent another disaster. However, efforts are being made to install more pumps and ensure that nothing like the tragedy that occurred on August 26, 1986, will ever happen again.

Sources

The Lake Nyos Disaster, retrieved 11/24/09, geo.arizona.edu/geo5xx/geos577/projects/kayzer/html/lake_nyos_disaster.html

Fink, Micah, Volcanic Killers, Degassing Lake Nyos, retrieved 11/24/09, pbs.org/wnet/savageplanet/o/volcano/01/indexmid.html

Lake Nyos (1986), retrieved 11//24/09, geology.sdsu.edu/how_volcanoes_work/Nyos.html