Natural disasters come in many forms. From tornadoes, to hurricanes, to volcanic eruptions and everything in between, Mother Nature has many ways to unleash her fury on humanity. Most types of natural disasters come with at least some sort of warning. For example, bad storms can presage a tornado, and hurricanes can be predicated days ahead of time.
However, there is one subset of disaster that occurs with little or no warning. It is silent, invisible, and deadly. Such an event happened in the environs around Lake Nyos in Cameroon, Africa, on August 21, 1986, when the lake released a deadly cloud of CO2 that killed over 1700 people.
Lake Nyos sits in the crater of an extinct volcano. Its lower levels are rich in CO2 bubbling up from the remnants of the volcano. This typically was not a problem, as the heavier waters of the surface layers kept the gas rich deeper waters under enough pressure that it was kept in solution. However, in the days leading up to the tragedy, there had been a lot of rain. This cooler water was denser than the warmer lake water, and essentially overturned the upper layers of the lake, essentially flip-flopping the upper and lower layers of the lake. This made the carbon dioxide rich lower layers rise to the surface and release the deadly gas all at once.
The gaseous cloud quickly swamped the shores of the lake and quickly traveled downhill to the surrounding villages, where people asleep in bed were suffocated without even knowing what had happened. Those who were awake found themselves weak and disoriented. Some 1700 people, 3000 cattle, and innumerable wild animals died in the tragic event.
These days, Lake Nyos is quiet. French scientists installed plastic piping in the bottom of the lake to slowly vent the deadly gasses that accumulate in the depths. This has changed the lake from its former pristine blue color to a rusty red, but that is a small price to pay for preventing the tragedy of 1986 from happening again.