August 21, 2012 - Eruption of Lake Nyos

– 1986

All my life I have heard of volcanoes erupting...but I didn't know that lakes could erupt!

Lake Nyos, in the African nation of Cameroon, is a crater lake that lies on the side of an inactive volcano. It is saturated with carbon dioxide, which seeps up from a magma chamber below the lake. Usually the carbon dioxide stays dissolved in the bottom layers of the lake water, but over time the water becomes supersaturated.

When the lake is supersaturated with CO2, and an earthquake or landslide occurs, a lot of the carbon dioxide can suddenly come out of solution and erupt from the lake, overflowing the water's edge and pouring down valleys, suffocating animals and people.

This is called a limnic eruption, and we only know of two such events. (We only know of three lakes in the whole world that are saturated with CO2 saturation—and they're all in Africa!) In 1984 another supersaturated lake in Cameroon suddenly outgassed carbon dioxide, killing 37 people. This 1986 overturn of Lake Nyos was far more tragic: 1.6 million metric tons of CO2 were suddenly released in a cloud that rose at a speed of nearly 100 kilometers per hour (62mph). A fountain of water and foam 91 meters (300 feet) high formed at the surface of the lake, and a wave at least 24 meters (80 feet) high washed the lake's shores. The gas flowed down several valleys—being heavier than air, it hugged the ground—and killed around 1,700 people!

Scientists aren't even sure what triggered the eruption of Lake Nyos. It may have been a landslide, a small earthquake, or even a small volcanic eruption on the bed of the lake. However, witnesses did not feel any tremors on the morning of the disaster.

Whatever triggered the limnic eruption, the normally blue waters of the lake turned deep red (because iron-rich water from the deep rose to the surface and were oxidized by the air), the level of the lake dropped by about one meter (3 feet), and trees near the lake were knocked down!

Scientists are trying to prevent another such disaster by degassing the lake. Some French scientists have installed degassing columns; they pump water from the bottom of the lake until the loss of pressure begins to release the gas and makes the process self-powered.

Also on this date:

Anniversary of the theft of the Mona Lisa

Anniversary of the Voyager 2 fly-by of Triton