Lake Nyos incident: The lake did not overflow, but more than a thousand people suffocated to death

In the summer of 1986, a villager near Lake Nyos in Cameroon, Africa woke up groggily, only to find that none of his family members and neighbors could wake up - the entire village was dead silent, livestock had died in droves, and even birds, beasts and reptiles had disappeared.

Less than a month after the Lake Nyos disaster | Source: Wikipedia

More than 1,700 people and 3,500 livestock died in a short period of time in villages within 25 kilometers of Lake Nyos, not just in the villages closest to the lake. According to eyewitnesses, the originally clear blue water of the lake once turned into a terrifying crimson color.

Livestock killed in Lake Nyos disaster

The culprit of this horrific "massacre" was Lake Nyos, which the villagers depended on for their livelihood. At that time, the villagers were still on their daily track, the lake did not flood, and there was no "water monster" causing trouble, but "killing people" was invisible overnight.

Satellite image of Lake Nyos | Source: Wikipedia

In fact, for Lake Nyos, it just burped on August 21, releasing a lot of gas, a phenomenon geologists call "limnic eruption". You may think that such a lethal gas must be some kind of poisonous gas, but in fact, it is between your breath - the main component of this "burp" of Lake Nyos is carbon dioxide.

Some survivors said they smelled gunpowder or rotten eggs, and had symptoms such as burning eyes and nose, and coughing. They may have inhaled irritating gases containing sulfur and hydrogen, such as hydrogen sulfide. However, according to the analysis of the composition of the lake water, the protagonist of this lake bottom eruption is odorless carbon dioxide, but the human sense of smell is also very sensitive to the smell of small amounts of sulfide. So, how can carbon dioxide, which is obviously non-toxic, cause death? The answer is simple - carbon dioxide is denser than air. It is estimated that the amount of gas released from the bottom of Lake Nyos reached 1.2 cubic kilometers. The huge cloud they formed spread and settled to the surrounding area, displacing a large area of ​​air.

As long as the concentration of carbon dioxide reaches 30%, it will cause coma, not to mention being submerged in an air mass that is almost entirely carbon dioxide. If the air mass stays for a long time, people and animals will be deprived of oxygen and will suffocate. But why did the originally calm Lake Nyos suddenly erupt? In fact, the calmness of Lake Nyos is just an appearance. Its true identity is a young crater lake on the Cameroon volcanic line, formed by the accumulation of water in the low-lying crater. And deep in the bottom of the lake, there has been a lot of magma surging secretly.

The volcanic lake and the magma chamber underneath | Image source: Wikimedia Commons

The results of carbon 14 analysis of carbon dioxide at the bottom of the lake show that they almost all come from magma deep in the earth's crust. As the pressure of magma decreases as it rises to the surface, it releases carbon dioxide and volatile gases. Carbon dioxide is input from underground into Lake Nyos day after day, making the carbon dioxide concentration in the lower layer of the lake water supersaturated, just like continuously producing soda, but the amount of gas dissolved in this "soda" is as high as 90 million tons. Under normal circumstances, the excess gas in the lake water will circulate naturally with the temperature changes of the four seasons, and will slowly be released into the surrounding air, instead of "lurking" in it all the time. However, the area where Lake Nyos is located has a high temperature all year round, the upper lake water has a high temperature and low density; the lower layer has a low temperature, which is just enough to dissolve more carbon dioxide.

This has planted a time bomb. Once the stratified lake water is greatly disturbed and internal waves are triggered, the lower lake water will churn up like a soda that is shaken vigorously, and effervescence will occur, which will then erupt a large amount of gas. Schematic diagram of the principle of lake bottom eruption | Source: Wikimedia Commons

It is estimated that the amount of carbon dioxide emitted by Lake Nyos is as high as 100,000 to 300,000 tons. On the night of the disaster, a series of "rumbling" sounds were heard. Based on traces such as fallen trees around the lake, investigators speculated that a hundred-meter-high water column and foam had been ejected from the lake, causing 25-meter-high waves. After a large amount of gas was released, the lake level dropped by nearly 1 meter. The deep iron-rich lake water rose to the surface of the lake and was oxidized to rusty red, making it look even more bloody. However, what exactly alarmed Lake Nyos remains a mystery. One speculation is that it was a volcanic eruption. However, the lake water samples were not enriched in sulfur, chlorine or fluoride, which are the characteristic components of volcanic gases. And the lake water temperature did not increase significantly. There is also speculation that it was an earthquake, but most eyewitnesses did not feel the tremor.

Image source: Wikipedia

The most likely speculation at present is that the landslides caused by the continuous rainfall are indeed signs of landslides around the lake, but there is no direct evidence that it caused the lake bottom eruption. In fact, before the Lake Nyos disaster, a similar incident had already occurred two years ago. On August 15, 1984, Lake Monoun, also in Cameroon, erupted from the bottom of the lake, killing 37 people.

Lake Monoun | Source: Wikipedia

Rescuers found a cloud of fog near the accident site, which dissipated after 3 to 4 hours. The results of subsequent lake water sample analysis still pointed to carbon dioxide. Unfortunately, no one expected the more tragic disaster that followed.

Exhaust pipes on Lake Nyos are pumping out water and exhaust | Source: Wikimedia Commons

After years of investigation and research, the local government installed exhaust pipes at the bottom of the two lakes to pump up the water from the bottom of the lakes and slowly discharge the carbon dioxide to prevent them from "exploding" again.

Exhaust pipe principle | Source: Wikipedia

The same risk exists at Lake Kivu, on the border between Rwanda and Congo in Africa. It is 2,000 times the size of Lake Nyos and is home to more than two million people.

Lake Kivu | Source: Wikipedia

Under the action of volcanoes, there is not only enriched carbon dioxide, but also flammable and explosive methane, which the local government extracts as energy. Lake Kivu erupts periodically about once every 1,000 years, bringing devastating disasters to surrounding organisms. However, because Lake Kivu is so large, it is not realistic to install enough exhaust devices.

After the Lake Nyos disaster, people began to pay attention to this matter. There are only three lakes in the world that are oversaturated with carbon dioxide and have the risk of eruption. If scientists had not let the truth come to light, the legend of the "Lake Nyos Monster" would probably have been born there. However, a "mood swing" of nature is much more destructive than a monster. Whether it is the lake "angry" or the people "angry", the most feared thing is that they can no longer bear it and are about to explode. It is better to relieve stress more often in daily life.

Written by | Mirror

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