Killer lake – A Look at the Nyos Lake Gas Eruption 1986

By Visio Roughton

Lake Nyos is a deep, picturesque lake located in the Northwestern Region of Cameroon, about 196 miles away from the country’s capital Yaoundé. The lake itself sits on the side of a dormant volcano at a point just above a magma chamber that has been known to leak Carbon Dioxide (CO₂) into the lake and once mixed with the water, the CO₂ became carbonic acid. As gas continued to spill into the lake, it gas came to settle at the bottom of the lake where it would stay there and continue to increase in volume until the night of August 21st, 1986. 

A Silent Killer

Around 10 pm on August 21st, 1986, people from a market town surrounding Lake Nyos reported hearing a sudden rumbling noise that they described as “distant thunder.” As the rumble shook the area, a wave of water exploded from the lake, drowning the lands and flattening nearby trees and crops. The farmers who left their homes intending to investigate the strange noise passed out. This trend continued as within seconds of the rumbling, both humans and animals began to drop dead without warning, or clear cause. 

A Mazuku (something that comes from the Swahili word for “evil winds”. This specific term refers to the clouds of carbon-dioxide heavy gasses that escape through vents in volcanically and tectonically active areas) that had engulfed the valleys around the lake, predominately the area that lay north of Lake Nyos. The villages of Cha, Nyos, and Subum were the worst affected; with over 1,700 people dying in the initial gas explosion along with around 3,500 livestock. The levels of carbon dioxide were so high that people died immediately where they were at the moment the gas exploded from the lake. It is noted that of all the residents of Nyos and Kam, villages first struck by the Mazuku, only four people survived, and this is attributed to the fact they had been located at a higher elevation. 

It took two days for the gaseous cloud to finally dissipate, and by August 23rd, it had finally cleared, allowing people from unaffected villages to venture into the area.

Aftermath – Rescue Efforts and Understanding the Disaster

When rescuers reached the area, they found that the bodies of both the humans and animals had nothing on their bodies to indicate how they died. A research team composed of scientists from France and the United States arrived to examine the scene around the same time and found that the body of Lake Nyos had changed. Known for its typically vibrant blue water and vegetation, it had turned a brown, rusty color. Scientists deduced that the deaths could be attributed to the lake, however what exactly had happened did not become clear until much later. 

Through extensive research and examination of the lake and the aftermath of the deaths, it was discovered that the Mazuku and subsequent flood were both the result of a rare natural event known as a limnic eruption. The carbon dioxide that had spilled into the lower levels of the lake had not risen to the surface because it was held down by the pressure of the water above. There was no outlet for the gas to escape through, thus the amount of it continued to increase. Although scientists have numerous theories about what actually led to the explosion of CO2 from the lake, most agree that a landslide or earthquake was likely responsible. 

Either event would have created enough disturbance that it allowed the gas-laden deep water to rush upwards and release over 1.6 million tons of CO₂ in a matter of minutes. The volume of the gas and its sudden, rapid release is part of the reason why this event was so deadly. It was in part due to a lack of knowledge around such an event, and thus no way to warn nearby people of the lake’s deadly potential.

Limnic Eruptions – History and Prevention

Although limnic eruptions are rare, they are not unheard of. Two years before the events of August 21st, 1986, Lake Monoun, a body of water 62 miles southeast of Lake Nyos had experienced a similar event, though on a much smaller scale. A third lake, Lake Kivu located on the border of Rwanda and the Democratic Republic of Congo also had scientists worried as it is 2000 times the size of Lake Nyos and has the potential to store up more gas. Not only would carbon dioxide be a concern should the lake suffer a limnic eruption, but high amounts of methane gas as well due to the bacteria that inhabit the lake. 2 million people live near Kivu, and sediment layers indicate the lake has not erupted in over 7,000 years. An eruption at that scale would have catastrophic results, and scientists wanted to prevent that from happening, as well as prevent a repeat of the Lake Nyos and Monoun eruptions.

To combat the build-up of gas at the bottom of Lake Nyos, engineers installed vertical pipes that extended from the lake’s bottom to the surface. The process relied on a simple but effective procedure: 

A small amount of water would be pumped up to the surface of the lake, allowing small amounts of carbon dioxide to escape the base of the lake at a controlled pace. The build up and release of the pressure created a self-sustaining pump that could move water on its own and continuously vent the gas without the need of an external energy source.

The first degassing pipe was installed in 2001 at Lake Nyos and then two additional pipes were installed in 2011 to further facilitate the degassing of the lake. A similar system was implemented at Lake Monoun, and due to the high levels of methane, a methane extraction machine was installed at Lake Kivu. 

There will never be a surefire solution to mitigate the threat of limnic eruptions, just as there can never be any entirely surefire way to avoid destruction from earthquakes or tsunamis. However, steps can be taken to help prevent worst case scenarios from coming to fruition. 

In the wake of the tragedies at both Lake Nyos and Lake Monoun, scientists realized they had to find solutions that could help lessen the impact of another potential gas explosion from these lakes. Lessons were learned and attention was focused on studying limnic eruptions, allowing for a new understanding of the invisible threat posed by these normally beautiful and serene volcanic lakes.