Lake Nyos is a crater lake located in the Northwest Region of Cameroon, nestled within the Oku Volcanic Field. This deep body of water became the site of a devastating natural disaster in 1986. The catastrophe involved the sudden, silent release of a massive, invisible gas cloud, which swept through the surrounding valleys with lethal speed. The event shocked the global scientific community and highlighted a previously unrecognized geological hazard associated with certain volcanic lakes.
The Catastrophic Night of August 21, 1986
The disaster began late in the evening of August 21, 1986, when a deep rumbling sound emanated from the lake. This was quickly followed by a geyser of frothy, white water that shot nearly 100 meters into the air, causing a substantial wave to crash onto the lake’s shores. The water of Lake Nyos turned a dark, rusty red color due to the upwelling of iron-rich water from the lake’s depths.
A dense, invisible cloud then began to flow rapidly down the valleys radiating from the lake, traveling at speeds estimated between 20 and 50 kilometers per hour. This cloud, being heavier than air, hugged the ground and spread across the low-lying terrain, reaching villages up to 25 kilometers away. In the villages of Nyos, Kam, Cha, and Subum, people and livestock were suddenly overcome by the suffocating gas. The deadly blanket of gas killed approximately 1,746 people and 3,500 livestock in its path.
The Mechanism of a Limnic Eruption
The catastrophic event at Lake Nyos was a limnic eruption, a rare natural hazard where dissolved gas suddenly erupts from deep lake waters. This phenomenon occurs in meromictic lakes, which have stable layering where bottom water layers do not mix with surface layers. Lake Nyos is a volcanic crater lake, and the source of its danger is a pocket of magma beneath the lake bed that continuously percolates carbon dioxide (\(text{CO}_2\)) into the deep water.
The immense pressure at the lake’s maximum depth of 208 meters allowed a massive amount of \(text{CO}_2\) to dissolve and accumulate in the bottom water, reaching near-saturation levels. Dissolved \(text{CO}_2\) increases the water’s density, which helps maintain stable stratification, trapping the gas under the weight of the water column. The gas release was triggered by an event—likely a landslide, rockfall, or cool surface water input—that disturbed the water layers, pushing the gas-saturated water slightly upward.
As the water rose, the hydrostatic pressure rapidly decreased, causing the dissolved \(text{CO}_2\) to effervesce out of solution, similar to opening a shaken soda bottle. The formation of gas bubbles made the water column less dense and more buoyant, accelerating the rise of deep water and creating a self-sustaining chain reaction. This massive outgassing released an estimated 100,000 to 300,000 tons of \(text{CO}_2\) from the lake, forming the cloud that flowed through the valleys.
Immediate Aftermath and Long-Term Human Impact
The first responders found a scene of bodies lying where they had instantly collapsed, with no signs of struggle or physical injury. The gas cloud, which was primarily carbon dioxide, killed by displacing the oxygen in the air, leading to rapid asphyxiation. Victims succumbed to \(text{CO}_2\) poisoning, which turned internal fluids acidic and accelerated the loss of consciousness.
Thousands of survivors fled the area, many of whom suffered lasting health issues, including respiratory problems and pressure-induced skin lesions. The disaster devastated the local farming economy through the loss of livestock and forced the displacement of approximately 4,000 inhabitants.
The Cameroonian government and international aid organizations struggled to comprehend the scale of the tragedy, as the event was unlike any previously recorded natural disaster. The area was eventually designated an exclusion zone, and the long-term response focused on understanding the threat to prevent a recurrence. Scientists classified the limnic eruption as a distinct type of hazard event.
Current Degassing Operations and Mitigation
The danger of a recurring eruption led to international efforts to mitigate the threat through an engineering solution. Scientists developed a plan to artificially degas the lake by installing vertical pipes that reach into the \(text{CO}_2\)-rich deep waters. The first permanent pipe was installed in 2001, followed by two additional pipes in 2011.
These pipes operate on a self-siphon principle, where a small amount of deep water is initially pumped to the surface to start the flow. As the pressurized water rises and the pressure drops, the dissolved \(text{CO}_2\) begins to effervesce, forming bubbles that create a powerful, self-sustaining upward thrust. This process allows the \(text{CO}_2\) to escape harmlessly into the atmosphere.
The degassing operations have significantly reduced the concentration of \(text{CO}_2\) in the lake, lowering the risk of another catastrophic event. However, the geological source of the gas remains active, and ongoing monitoring is necessary to ensure the infrastructure functions effectively. The success at Lake Nyos provides a model for managing the risk posed by other limnically active lakes, such as Lake Kivu in East Africa.