This post is a sidebar to the “Can CO2 Form a Blanket?” post.
Lake Nyos is a deep crater lake located on the side of a dormant volcano in Cameroon. The lake sits atop a pool of magma that releases CO2 into the waters to the degree that, back in the early 1980s, the lake was saturated with CO2. (Actually, the lake was found to be “supersaturated” — temporarily holding more CO2 than it should at equilibrium, like a just-opened beer.) At the depths of the lake, the water pressure holds (literally) tons of CO2 in solution, in exactly the same way that the pressure in a beer keg keeps high levels of CO2 dissolved in beer. In the upper levels of the lake, progressively less CO2 is trapped.
In 1986, a violent outgassing (perhaps caused by a landslide into the lake) caused CO2 to erupt from the lake and flow down the slope of the volcano. The level of the lake, whipped into a foam, was lifted about 100 ft. above it’s normal level. Scientists estimate the gas flowing down the volcano was over 150 feet thick and travelled at speeds up to around 30 mph. In towns in the valleys below the lake, 1,700 people suffocated (as did about 3,500 head of livestock).
After the eruption, scientists began looking for other lakes that could pose a danger in this way. (One lake near Nyos, Lake Monoun had erupted in 1984, killing 37.) Lake Kivu in The Democratic Republic of Congo was also found to be saturated with CO2 (in addition to containing large amounts of methane). Scientists are concerned about this lake because it is 2,000 times as large as Lake Nyos and is in a more heavily populated area.
Lake Nyos today is being degassed. A long tube,extending deep into the lake from a floating platform, was placed in the lake and a constant geyser of bubbly water erupts from it, taking CO2 out of solution. However, the lake remains a concern because the natural “dike” that holds the water on the side of the volcano is eroding. If it gave way, not only would all the water rush into the surrounding valleys, but an enormous amount of CO2 — much more than in the 1986 lake eruption — would be released.