Lake Nyos, Killer Lake
In 1986 Cameroon’s Lake Nyos exploded.
The cow herders and farmers who lived in the remote area first heard a deep rumbling from the lake and then watched as the lake exploded, a geyser of water shooting straight up into the air and coalescing in a cloud that eventually reached more than 300 feet above the surface of the water. Slowly, hugging the ground, the cloud began to move, floating off the lake and over several small settlements. People in its way fell where they had been standing, cattle collapsed in the fields, and birds fell from the sky.
When officials in Wum, the regional capital, first heard of the disaster, Emmanuel Ngu Mbi, local chief of Health Care, began riding his bicycle towards the lake. When he reached Cha, a village near the scene, he smelled something strange, felt dizzy, and collapsed eventually coming too after a period of unconsciousness. He continued on and noticed a dead antelope, which he picked up and tied on his bicycle rather than see it go to waste. A short distance later, he noticed two dead rats, and further on, a dead dog and other dead animals, all of which he thought might have been killed by a lightning strike.
Then came on the village of Nyos and was stunned.
No one was alive in the village, and the dead were strewn about mixed with the bodies of cows and local wildlife.
Mbi threw down his bicycle and ran all the way back to Wum to report the calamity.
For two days the cloud had moved across northern Cameroon before finally dissipating and allowing rescue workers to enter the area. There they found it had left 1,746 dead behind, including people who resided as much as fifteen and a half miles away from the lake. The lake, which the local people had always called the “Bad Lake,” had changed as well. Where it had been a pristine blue, it had now darkened to a rust-like color, and it was shallower than it had been.
“I could not speak,” Joseph Nkwain, who had survived the cloud later said. “I became unconscious. I could not open my mouth because then I smelled something terrible. I heard my daughter snoring in a terrible way, very abnormal.” He struggled to get to her side, he said, but collapsed on the way.
When he finally did reach her it was too late, she too was dead.
What had happened?
Many of the more traditional of the local people blamed the disaster on the evil spirit woman who was known to inhabit the lake and to periodically leave it to wreak vengeance on those who lived nearby. Others in the area attributed the disaster to a prominent local chief, popularly known as the Lake Chief, who died in 1983 and had willed that his best cow be given up for ritual sacrifice. When the chief died, however, kinsmen of his decided the designated cow was too big for sacrifice and substituted a slimmer one disregarding the Lake Chief’s will. The explosion of the lake, some local people said, was a sign of the Lake Chief’s annoyance.
After the explosion at Lake Nyos disaster western investigators, primarily from the United States and France swarmed the area looking for a cause.
They quickly found it.
“You can’t see it,” one investigator said. “You can’t smell it. It’s the perfect crime.”
Studies of the area revealed that Lake Nyos is a crater lake that had been formed by the eruption of local volcanoes some 400 years ago. Volcanic activity still going on underneath the lake, investigators discovered, was releasing carbon dioxide (CO2) that was gradually seeping into the lake water and building up there. This happens in all such crater lakes, they said, but Lake Nyos is different. Generally the gas that accumulates in such a lake is dissipated when colder weather causes the surface water of the lake to also get colder (and heavier) and sink bringing the underlying water to the top and releasing the accumulated gas, a process commonly known as “turning over.”
That doesn’t happen to Lakes Nyos.
Cameroon is a tropical area. It doesn’t get cold, and the lakes do not “turn over.” The surface water of tropical lakes does not sink allowing the bottom water to rise to the surface and, in the case of crater lakes, expel its accumulated gases. The gases just continue to seep into the lakes, the concentration continues to rise, and the lakes finally “explode” when some external event triggers a release of the accumulated gas all at once. In Lake Nyos’s case that release was of a full third cubic mile of CO2. At the time of the lake’s explosion and the release of its accumulated gas, the scientists estimated, Lake Nyos had reached a point of saturation there were five gallons of carbon dioxide for every gallon of lake water.
But after the lake’s explosion, it was an unanswered question as to what had triggered the release. Scientists believe the CO2 had been trapped in the bottom of Lake Nyos—and gradually growing—for a long time, held down by the weight of 682 feet of water. On the day of the eruption something external triggered the release. It could have been a slight volcanic eruption under the lake or perhaps was the result of a cold rain that had fallen shortly before the explosion infusing the lake’s surface water with a shot of colder, heavier water. But many investigators believe it was a rockslide somewhere along the shore of the lake that tumbled rocks into the water, rocks that sank into the gas layer releasing some of the accumulated carbon dioxide initiating the explosion.
Whatever triggered the 1986 explosion, investigators concluded, the lake had been releasing these same killer clouds of carbon dioxide for centuries.
Which explains the legends of evil spirit women that “came about because of gas bursts in the past," William Evans, a geochemist with the U.S. Geological Survey who investigated the disaster, said.
What is being Done
The Cameroonian government has since acted to prevent further eruptions and loss of life. With assistance from Evans' team, it has installed CO2 monitors on the lakeshore, monitors that were hooked to sirens that would sound if too much carbon dioxide enters the air. At the same time, residents have been told they should head for higher ground if the sirens sounded. (In the Lake Nyos disaster only a half-dozen residents out of the village of Nyos’s population of 800 survived, and they were people who had fled to local hilltops when the cloud, which was heavier than air approached their village). In addition, in 2001 a French team sank a six-inch plastic tube 666 feet down into the lake to where it reached the gas layer and triggered a controlled release of accumulated gas. Today the lake contains roughly eighty percent less gas than it did at the time of the 1986 explosion and additional pipes have been proposed.