The 1986 Lake Nyos Disaster occurred when volcanic carbon dioxide (CO2) gas erupted from beneath an African lake in Cameroon, bubbling to the surface and forming a deadly cloud. There was no huge eruption, no great boom or blast to warn people. What resulted however was like a scene from a horror movie. The deadly gas flowed down valleys and into villages, asphyxiating 1,746 people and 3,500 livestock. By morning, villagers and animals within 25 kilometers of the lake lay dead in homes and fields. It occurred decades before the first Ebola Epidemic. How did such a tragedy come about?
The republic of Cameroon, situated in equatorial Africa on the Gulf of Guinea, was a former German colony, then a French and British colony, that gained its independence in 1960. It is bordered by Chad, Nigeria and the Congo. Lake Nyos is a small, 2 km long, 200 m deep crater lake located in northwestern Cameroon near the border with Nigeria. The region is known for its occasional volcanic activity, but nothing like this disaster.
Most of the people in rural Cameroon are farmers or herders, this included the villages and farms on the slopes of the crater lake. Residents knew the lake as blue and usually still. August 21, 1986 began as a typical summer day. Men and women labored from dawn till dusk in the fields. Children attended their schools. By late evening, they had completed their dinners and parents put children to bed. The summer evening air was still hot with relatively little breeze.
Sometime between 9 and 10 pm, villagers in the valley heard a strange rumbling noise, much like thunder, but without any lightning. Those people closest to the Lake Nyos described hearing a distant bubbling noise. A frothy spray emerged from the lake, with a whitish cloud developing on the entire surface. Lake Nyos is surrounded mostly by bluffs, some up to 100 m high. The cloud mushroomed in size until it overflowed the crater rim and began to flow down into nearby valleys.
When farmers near the lake left their houses to investigate, they suddenly lost consciousness.
There was no warning, no time to scream or run. Most were dead in a few breaths. People and animals all around them began losing consciousness and collapsing to the ground. It a few minutes, most had suffocated. In Nyos and Kam, the first villages hit by the cloud, all but four people on higher ground died. The valley split and the deadly cloud followed each path, killing people up to 25 kilometers away from the lake.
Some survivors overtaken by the deadly cloud smelled a sulfurous, rotten egg odor and feeling a warm sensation on their skin before losing consciousness. After rescue, some remained unconscious in a coma for up to 36 hours. They woke up to a scene of mass death.
Such a cloud is called a mazuku, a deadly blanket of carbon dioxide mixed with air. Magma pockets under the lake had leaked CO2 into the water in high concentrations. Then some activity caused it bubble up to the surface. The large cloud of deadly gas is estimated to have grown to 100 meters (330 feet) tall before flowing over the rim and down into the valley.
The next day, pockets of gas lingered in low lying areas, causing new fatalities when people unwittingly walked into the gas pockets. Over the next two days, people from surrounding areas rushed to the valley. They found thousands of corpses, both human and animal, lying on the ground where they had dropped. Cattle, sheep, goats, pets, birds, and even insects were all killed. It was as if time had stopped. A putrid smell of rotting eggs would cling to the earth for months.
A government rescue team did not arrive until 36 hours later.
Assisted by the Cameroon military, everyone wore full face masks, protective gear and oxygen tanks on their backs. The approximately 5,000 survivors were all in comas that ranged from six to 36 hours in length. They reported falling unconscious and waking up dazed. The lucky ones had escaped death because they lived on higher ground.
“I could not speak. I could not open my mouth because of the terrible smell. When crossing to my daughter’s bed, I collapsed and fell. I was there till nine o’clock in the morning until a friend came. I wanted to speak, but my breath would not come out. My body was completely weak. I managed to go over to my neighbors’ house. They were all dead.” – Survivor Account.
By August 23rd, the cloud had blown away. After being unconscious for up to a day and a half, some survivors revived only to find that their family members, neighbors, and livestock were dead. Around 1,746 people died in the towns of Nyos, Cha, Fang, Mashi, and Subum. Most residents were farmers.
Sadly, with so many corpses, the dead could not receive individual funerals, so rescuers dug mass graves. Some developed respiratory issues. Pregnant women suffered miscarriages; others had pneumonia. A few committed suicide after seeing the horror of so many dead or losing all family members.
About 3,500 livestock also perished and had to be burned in large pyres. Lake Nyos itself had changed, too. It was now significantly shallower. Dead fish floated on its surface. Its formerly picturesque blue hue had darkened and turned an ugly rust color.
The Cameroonian government in Yaoundé initially suspected an act of terrorism, or the illegal dumping of chemical wastes into the lake. More traditional villagers in Njindoun believed legends that evil spirits periodically left the lake and killed neighboring people. These legends likely came about because of past gas bursts.
All evidence pointed towards death from CO2 asphyxiation.
Concentrations of just 10 percent lead to rapid unconsciousness and coma. Forty percent concentrations are almost immediately lethal within minutes. Many of the victims seemed to have died very quickly, suggesting very high CO2 concentrations.
Carbon dioxide kills by first shutting off people’s consciousness, then their breathing. Where the CO2 concentration was 15 percent or less, people fell into a coma but later revived. Individuals who inhaled more than 15 percent CO2 stopped breathing in minutes and suffocated. The sulfurous odor was attributed to small amounts of hydrogen sulfide mixed with the CO2.
Geologically, the Lake Nyos disaster was a limnic or gas eruption. This happens when a volcanic crater lake suddenly releases a large amount of dissolved gases in the water. Gas releases occur when pressure builds up from geothermal activity at the lake’s bottom. When the pressure becomes too great, gas rapidly escapes to the surface and forms a heavy, toxic cloud. The cloud blankets the ground, displacing oxygen and quickly asphyxiating people and animals.
Geologists reasoned that CO2 had been trapped in the bottom of Lake Nyos for a long time, held down by 208 meters (682 feet) of water. On the day of the gas eruption, something external triggered the release of gas. Most likely the vibration a simple rockslide from one of the lake’s steep walls.
The gas release was not a volcanic eruption.
The lake water was not unusually warm and the bottom was undisturbed. Magma beneath the earth seeped carbon dioxide into the deep lake waters, where it dissolved. When the CO2 content became supersaturated, CO2 erupted to the atmosphere. About one cubic kilometer of gas escaped, enough to lower the entire lake level by more than one meter.
Lake Nyos is in the Oku Volcanic Field, part of a 1,600 km-long chain of volcanoes that runs from Nigeria and Cameroon into the mainland. Lake Nyos sits on the edge of an inactive volcano and a magma pocket. The lake changed colors when the escaping gas carried oxygen-poor, deep lake water with it. When this water reached the surface, dissolved iron reacted with oxygen in the air, creating iron hydroxide that stained the lake yellow-brown for several month.
Once the cause was determined, the Cameroonian government acted accordingly. Teams installed CO2 monitors on the lakeshore, hooked to sirens that would sound if too much gas entered the air. People knew the alarms meant they should go immediately to higher ground. The government relocated several communities and discouraged residents from returning to the lake.
A refugee camp for villagers, situated 25 kilometers from the lake, became a permanent home to many. Most of the survivors still alive have fresh memories of what happened to them that horrible night. They lost family, their land, and their herds. The Cameroon government promised to assist them by building new houses and giving them funds to start agriculture again elsewhere. The victims say they still have not received the promised compensation.
The survivors say since then, they have been forgotten and abandoned.
To prevent a recurrence, measures were implemented to manage Lake Nyos. Geologists opted for a gradual degassing of the lake, but this took decades to enact. Money and decent roads into Nyos weren’t plentiful. In 2001, French engineers sunk a 6-inch (15-cm) plastic pipe 666 feet (203 meters) into the lake until it reached the gas layer. Frothy CO2 shot out the top like a shaken champagne bottle. Authorities installed two more pipes in 2011.
It has always been the wish of the survivors to return to their ancestral villages. But Cameroon’s Ministry of Territorial Administration, says it is still too dangerous, even with the degassing of the lake. Even so, some are ignoring warnings from the government and have returned to live and farm close to the lake once again. Today, Lake Nyos is degassed to about 80 percent of the level after the 1986 explosion. While the lake is significantly safer today, it still carries a hazardous risk level for those who dare venture near it.