The Lake Nyos Mystery: 1,700 Killed in a Single Night

1. Overview

On August 21, 1986, a massive release of carbon dioxide from Lake Nyos, a volcanic crater lake in northwestern Cameroon, suffocated 1,746 residents of nearby villages and around 3,500 cattle while they slept. This is why Korean-language urban legend posts describe the victims as “bodies without a single wound.” There had been no explosion, fire, or collapsed houses—only people and livestock lying dead.

Scientists later determined that the disaster was a “limnic eruption”: carbon dioxide that had accumulated in dissolved form at the bottom of the lake for a long time suddenly burst out. However, what disrupted the lake’s equilibrium has never been established with certainty. As a result, although the event is classified as a natural disaster, it has never quite shed its “mystery” label.

2. A Cloud Descends on a Sleeping Village

Lake Nyos lies inside an old volcanic crater in Cameroon’s Northwest Region, about 315 km northwest of the capital, Yaoundé. DW reported that the lake is part of the Oku volcanic field. According to an Instagram post shared on theqoo, the lake is not large, but its deepest point is more than 200 m below the surface. Villages including Nyos, Kam, Cha, and Subum lay along the valley below the lake, where residents raised cattle amid plentiful water and grass. The volcano was thought to have been dormant for a long time, so no one expected the lake to pose a danger.

Yet carbon dioxide rising from underground had been dissolving in the deep water and accumulating there over many years. Isaac Confor Nyilla, a Cameroonian geologist quoted by DW, said there had been no warning signs before the disaster. Investigators found that the upper layer of the lake contained oxygen-rich water, while the deeper layers were saturated with carbon dioxide. Hankook Ilbo and the post compare this to a sealed bottle of carbonated drink: once shaken or opened, the bubbles erupt all at once.

Reports differ on when the eruption occurred. The post and YTN place it at around 9 p.m., while Hankook Ilbo says it happened in the early hours of August 21. According to Hankook Ilbo, a column of water shot up 100 m from the lake, and waves reached heights of up to 25 m. Scientists estimated that between at least 100,000 and as much as 1.6 million tonnes of carbon dioxide were released. YTN gave the figure as “up to 1,600 tonnes,” which does not match the other estimates. Carbon dioxide is 1.5 times heavier than air, so rather than dispersing upward, it flowed down the mountainside. The post says the gas cloud, about 50 m thick, moved down the valley at 20–50 km/h and was difficult to see because it had almost no color or smell. Hankook Ilbo and the post place the affected area within a 25 km radius of the lake, while YTN said the gas reached areas around 100 km away.

3. A Silent Morning and the Survivors

The village was said to have been eerily quiet on the morning of August 22. The post reports that there were no sounds from chickens or cattle, and that livestock, wild animals, birds, and even flies had died. The cloud had dispersed and disappeared during the night. What remained were 1,746 dead, 845 injured, and around 3,500 cattle. Hankook Ilbo adds that more than 4,000 people in areas farther away were evacuated, and many suffered lasting effects such as difficulty breathing and paralysis.

Survivors gave similar accounts. A man named Joseph reportedly smelled a terrible odor before falling unconscious, then woke up about three hours later. According to the account carried by the post and YTN, he heard his daughter snoring strangely in the next room and got up, but then collapsed. His daughter was already dead. YTN reported that he gave this account in an interview with Professor Arnold Taylor of the University of Plymouth. The post says that everyone who woke up described the same thing: “I lost consciousness, and when I opened my eyes, everyone around me was dead.”

The description of the victims as having “no injuries” is not strictly accurate. A paper published in the British Medical Journal (BMJ) in 1989 reported that clinical findings among 845 survivors examined at hospitals were consistent with exposure to an asphyxiant gas. Rescue workers found erythema and blisters on the skin of some bodies and on 161 (19%) of the survivors who received treatment. These were initially suspected to be burns caused by acidic gas, but later investigations concluded that they were associated with exposure to carbon dioxide and the resulting coma.

4. The Lake Turns Red and the Cause Is Identified

The post says that when people went up to the lake several days later, they found that its clear blue water had turned a deep red. It explains that iron dissolved in the deep water had been stirred up and rusted on contact with the air. However, this account appears only in that post.

After the disaster, scientists from Cameroon and abroad began investigating and concluded that carbon dioxide dissolved in the deep water had escaped in a rapid chain reaction. According to DW, researchers have suggested that a landslide may have disturbed the gas-saturated water at the bottom and triggered the eruption. Hankook Ilbo reported that theories about the immediate cause differ. A similar event had already occurred: on August 15, 1984, Lake Monoun, about 100 km southeast of Lake Nyos, experienced the same phenomenon, killing 37 people. According to DW, the much larger Lake Nyos disaster occurred while scientists were investigating the Lake Monoun incident.

Measures were also taken to prevent a recurrence. According to Hankook Ilbo and YTN, the Cameroonian government and the international volcanology community installed equipment that pipes carbon dioxide out from the lakebed, and built a dam to prevent gas from overflowing beyond the lake. Hankook Ilbo reported that inspections of lakes with similar conditions found that the bottom of Lake Kivu in the Democratic Republic of the Congo—about 2,000 times larger than Lake Nyos—was supersaturated with carbon dioxide, prompting the implementation of preventive measures.

5. Authenticity Debate

The main questions are whether this disaster can be adequately explained as a natural phenomenon known as a “limnic eruption,” and how to interpret the fact that the trigger for the eruption remains unknown.

5.1. The Natural Phenomenon Explanation Is Sufficient

This position begins with the condition of the victims. Clinical findings among the 845 survivors who arrived at hospitals were consistent with exposure to an asphyxiant gas, and skin lesions initially mistaken for burns were ultimately associated with coma caused by carbon dioxide. Joseph’s account of an unusual smell, loss of consciousness, and waking about three hours later also fits this explanation. A scene in which people, livestock, and even flies all collapsed at once, without an explosion or fire, is consistent with oxygen being displaced from the air.

The second piece of evidence is that the phenomenon has occurred more than once. The same thing had already happened at Lake Monoun two years earlier, and researchers concluded that it was a limnic eruption. The fact that pipes were installed to remove gas from the lakebed, and that preventive measures were implemented after inspections of similar lakes such as Lake Kivu, also shows that this mechanism was accepted as a real-world explanation. The argument is that uncertainty about the trigger is not enough to cast doubt on the explanation as a whole. It is also argued that the lake’s red color is consistent with iron-rich deep water being overturned and brought to the surface.

5.2. Significant Questions Remain Unanswered

The opposing position begins by pointing out that there is no answer to the question, “What disturbed the lake?” According to Hankook Ilbo, no seismic waves were recorded at the time of the disaster. Sulfur compounds such as sulfur dioxide and hydrogen sulfide were detected, but no clear evidence emerged that a volcano had erupted underwater. A landslide has been mentioned only as a “possibility.” The post also says, “Even now, we don’t know for sure what it was,” while YTN reported that the cause remained unknown even around 30 years later. If the trigger for the eruption remains unexplained, can the event really be said to have been fully explained?

The BMJ paper also noted that the possibility of toxic factors other than carbon dioxide could not be ruled out. Given that the victims’ skin lesions were initially suspected to be burns caused by acidic gas, and that sulfur compounds were in fact detected, it is argued that it is too soon to conclude that carbon dioxide was the sole cause. YTN also reported that the reason large quantities of carbon dioxide were released from Lake Monoun remains unknown. These gaps have even given rise to conspiracy theories that the Cameroonian government and Israel conducted a secret bomb test. However, YTN provided no evidence to support this claim, which amounts to little more than hearsay.

Neither side disputes the fact that carbon dioxide had accumulated at the bottom of the lake. The unanswered questions are what directly triggered the eruption and whether factors other than carbon dioxide contributed to the disaster. These points have not been conclusively resolved.

6. Trivia

• Reports spell the survivor’s name differently. The post calls him “Joseph Nkwain,” while YTN gives it as “Joseph Niquan.” They appear to refer to the same testimony.
• Hankook Ilbo compared a limnic eruption to a body of highly concentrated carbonated water the size of a lake, while the post called it a “giant Coke bottle.”
• Citing an Al Jazeera report from December 2016, YTN reported that survivors of the disaster were planning to return to their former home 30 years later. On the 40th anniversary of the disaster, DW reported that survivors were still living with trauma.
• In a YouTube video by the French-language broadcaster TV5MONDE, it was stated that on August 21, 1986, 1,746 people and 3,500 cattle near Lake Nyos suffocated in their sleep.