40 years after the Lake Nyos disaster in Cameroon

Forty years after the catastrophic Lake Nyos disaster in Cameroon, the memory of the event continues to shape the lives of its survivors and the scientific community. On the night of August 21, 1986, Lake Nyos, situated in Cameroon’s Northwest Region approximately 315 kilometers northwest of the capital Yaoundé, unleashed a lethal cloud of carbon dioxide that swept through surrounding valleys and villages. The gas, which displaced oxygen in the air, led to the deaths of around 1,700 people and nearly 3,500 livestock, marking one of the deadliest natural disasters in the country’s history. The disaster caught everyone off guard. Isaac Konfor Njilah, a Cameroonian geologist and head of a laboratory in the Department of Earth Sciences at the University of Yaounde, described how the event unfolded with little to no warning. “We had no warning signals before it ever took place,” he stated. The lake, nestled within an ancient volcanic crater in the Oku volcanic field, had long been suspected of harboring dangerous conditions, but the scale of the tragedy was unprecedented. Scientific investigations following the disaster revealed that carbon dioxide from deep underground had been accumulating at the bottom of the lake for years. Trapped beneath over 200 meters of water, the gas had been dissolving continuously in the lake’s depths. Water, according to Njilah, has an insatiable appetite for carbon dioxide. Over time, this buildup created a volatile situation. When the delicate equilibrium was disrupted, possibly by a landslide, the gas erupted in a rapid chain reaction, forming a dense cloud that descended into nearby communities. This type of event, known as a limnic eruption, occurs when gas-rich deep waters suddenly rise to the surface, releasing large amounts of dissolved gases. While carbon dioxide is harmless at normal atmospheric levels, in high concentrations, it acts as an asphyxiant, pushing oxygen out of the air. Because the gas is heavier than air, it flows downhill, engulfing homes and farms where people and animals slept, leaving them unconscious and ultimately dead. The Lake Nyos disaster was not the first of its kind in Cameroon. Just two years earlier, on August 15, 1984, a similar event occurred at Lake Monoun, located about 100 kilometers southeast of Nyos. That incident resulted in the deaths of 37 people. Scientists were still studying the causes of the Monoun disaster when the even deadlier Lake Nyos tragedy occurred. Both events underscored the dangers posed by these lakes, which sit atop volcanic fields and can accumulate dangerous levels of gases. In the aftermath, researchers and engineers worked to mitigate the risk. Degassing pipes were installed in Lake Nyos to slowly release the accumulated carbon dioxide from the depths. These efforts have since reduced the threat significantly. According to Njilah, the lake no longer holds enough dissolved carbon dioxide to cause a recurrence of such a disaster. “The lake is very safe for the population to return,” he noted. Despite the safety measures, the psychological scars remain among survivors. Tsang Emelda Njah, who was five years old at the time, recalls the moment the disaster struck. “We were at home, and there was a big vibration of the house,” she recounted. “We thought it was just the house that was about to collapse. But we were not sure what it was. So we ran out.” Kum Samuel, who was 17, returned to his village and found a scene of devastation. He described seeing his parents and other family members lying lifeless, alongside livestock and wildlife, all victims of the gas. Many survivors were relocated to new settlements, yet the trauma persists. For them, the memory of that night remains deeply etched, a constant reminder of nature’s power and unpredictability. As the years pass, the lessons learned from Lake Nyos continue to inform both scientific research and public awareness, ensuring that such a tragedy is unlikely to repeat itself.