A limnic eruption is a rare natural hazard characterized by the sudden release of dissolved gases from deep lake waters. This phenomenon results in a potentially deadly gas cloud that can spread across the surrounding landscape. It is distinct from volcanic eruptions, though often linked to volcanic activity.
Understanding the Mechanism
Limnic eruptions occur in lakes where large quantities of gas, primarily carbon dioxide (CO2), accumulate in deep, cold waters. This gas often seeps into the lake from volcanic activity beneath the lakebed or from geothermal vents. The deep water, under high pressure, can dissolve significant amounts of gas, similar to how CO2 is dissolved in a sealed soda bottle.
A key condition for gas accumulation is thermal stratification, where lake water forms distinct layers that do not mix. The colder, denser water at the bottom remains undisturbed, allowing CO2 to build up to supersaturated levels. Lakes exhibiting this stable layering are called meromictic lakes. When this balance is disturbed by a trigger, such as a landslide, earthquake, or strong winds, the gas-saturated deep water is brought closer to the surface. The reduced pressure at shallower depths causes the dissolved CO2 to rapidly effervesce, leading to an explosive release.
Consequences and Documented Events
The immediate impacts of a limnic eruption can be significant. The explosive release of gas displaces large volumes of water, generating tsunamis that sweep across lake shores. The main danger comes from the large cloud of carbon dioxide released into the atmosphere. Because CO2 is denser than air, this cloud hugs the ground and flows into surrounding valleys, displacing breathable oxygen.
The lack of oxygen in these gas clouds causes rapid asphyxiation in humans, livestock, and wildlife. The two most well-documented limnic eruptions occurred in Cameroon, West Africa. The first happened at Lake Monoun in August 1984, resulting in 37 deaths. Two years later, in August 1986, a larger event occurred at nearby Lake Nyos.
The Lake Nyos eruption released an estimated 100,000 to 300,000 tons of CO2, killing approximately 1,746 people and 3,500 livestock up to 25 kilometers from the lake. Survivors described a rumbling noise and a cloud that flowed rapidly down valleys, leaving most victims dead in their sleep without signs of struggle. These events brought limnic eruptions to global attention, highlighting the unique nature of this rare disaster.
Detection and Prevention Efforts
Scientists monitor lakes at risk of limnic eruptions by measuring gas concentrations in deep waters, analyzing temperature profiles, and tracking seismic activity. These measurements help assess the level of gas saturation and the stability of the lake’s stratification. Identifying lakes with high dissolved CO2 concentrations is a primary step in hazard assessment.
The main prevention strategy for high-risk lakes involves controlled degassing. This method uses pipes to continuously pump gas-rich water from the lake’s depths to the surface, allowing dissolved gases to be released gradually and safely into the atmosphere. At Lake Nyos, a permanent degassing pipe was installed in 2001, with two additional pipes added in 2011, significantly reducing the CO2 concentration. Similar efforts at Lake Monoun have reduced gas levels to negligible amounts. While challenges like pipe corrosion and operational costs exist, these projects have proven successful in mitigating the risk of future limnic eruptions.