What Triggers a 'Killer' Lake to Explode?

Floods and wildfires frequently dominate headlines, but today, we're focusing on another rare type of natural disaster—one that hasn’t been recorded for over three decades. Though unusual, this phenomenon is not to be taken lightly, as it has the potential to obliterate entire communities with little to no warning.

This is the phenomenon of a limnic eruption. A limnic eruption occurs when lethal gases, such as CO2, violently escape from volcanic lakes. The destruction can unfold on multiple fronts: toxic clouds suffocate both humans and animals, while the sudden displacement of water can generate tsunamis. This very combination of events led to the tragic deaths of more than 1,700 individuals in Cameroon in 1986. Now, scientists are concerned that an even larger eruption may be looming.

A Recipe for Catastrophe

As you dive deeper, water pressure increases, which is why scuba divers need specialized gear to go beyond certain depths. This force, known as "hydrostatic pressure", refers to the pressure exerted on submerged objects from the weight of the water above. Generally, the pressure increases by 14.5 pounds per square inch (or 99.9 kilopascals) for every 34 feet (10 meters) of water.

Cold, high-pressure water allows gases to dissolve more easily. This is the key to understanding limnic eruptions. Such events can only occur in deep bodies of water where there is significant hydrostatic pressure at the bottom. Additionally, there must be a notable difference in pressure and temperature between the surface water and deeper layers (with the latter being colder).

Stratification acts as a barrier, trapping the dissolved gas at the lake's bottom, preventing it from depressurizing and escaping into the atmosphere. As the gas accumulates, it can reach dangerous levels. Explosions are unlikely in lakes where the upper and lower water layers mix regularly.

For a limnic eruption to happen, the water must continuously receive a supply of highly soluble gases like carbon dioxide (CO2) or methane. This is where volcanism comes into play. In areas with active volcanoes, magma deep within the Earth can leak methane, CO2, and other gases through thin sections of the crust. If a lake is above, these gases can enter the water through volcanic vents and other routes.

Up From the Depths

That brings us to Lake Nyos and Lake Monoun. They are both located in a volcanic field in Cameroon. Both lake bottoms are oversaturated with CO2, which underlying magma sends their way. On Aug. 15, 1984, some of the deep water in Monoun that had been loaded up with the dissolved gas ascended to the surface. No one knows why this happened; it's possible that heavy rainfall, and an earthquake or a landslide displaced some of the lake-bottom water. Regardless, as the water rose, the dissolved CO2 lurking inside it became depressurized and formed bubbles. Those bubbles drove even more of the water to the top of the lake, resulting in a massive, foul-smelling cloud of carbon dioxide gas.

Under the wrong set of circumstances, this gas is extremely dangerous to people. Large quantities of CO2 cling to the ground and displace oxygen, which can lead to death by suffocation. On that awful day in 1984, no fewer than 37 humans perished as a direct result of all the CO2 Monoun suddenly let loose.

Just two years later, on Aug. 21, 1986, Lake Nyos experienced a limnic eruption of its own. Once again there was a sudden, mysterious upheaval of CO2-laden water from its frigid, high-pressure depths. But this time, the body count was much higher: Carbon dioxide from the Lake Nyos disaster killed approximately 1,746 people and more than 3,500 domestic animals. Somewhere in the ballpark of 330,000 to 1.7 million tons (300,000 to 1.6 million metric tonnes) of CO2 gas burst out of the water with enough force to set off a 65.6-foot (20-meter) tsunami.

Is This Coming to a Lake Near You?

Concerns about a catastrophic limnic eruption in Lake Superior or Loch Ness are unwarranted, says University of Michigan geoscience professor Youxue Zhang. The most recent limnic eruptions took place in Lake Nyos and Lake Monoun, both situated just above the equator, where the temperature remains consistently warm throughout the year.

A limnic eruption cannot occur in temperate waters. In regions with extreme seasonal temperature changes (like the Great Lakes), lake surfaces often cool, causing the water at the surface to sink and swap with deeper layers. "Temperate lakes turnover annually, [so] it's unlikely that any gas would accumulate in the bottom waters," Zhang explains. "Without this gas buildup, lake eruptions are impossible."

However, Zhang and many of his colleagues are keenly interested in Lake Kivu, a 1,042-square-mile (2,700-square-kilometer) emerging vacation hotspot on the border between Rwanda and the Democratic Republic of the Congo. Why? Because it meets all the necessary conditions for a massive limnic eruption.

At the bottom of Lake Kivu, there are roughly 10.5 billion cubic feet (300 million cubic meters) of dissolved carbon dioxide and 2.1 billion cubic feet (60 million cubic meters) of methane. Should these gases erupt to the surface, the 2 million residents surrounding the lake could be at risk.

A potential solution to this issue involves capturing the gases as an energy resource using an extraction barge. KivuWatt, a unique $200 million project, utilizes a floating barge to extract water from the lake, siphoning off methane and channeling it to a nearby power plant to produce electricity for the region. It’s a case of turning lemons into electricity.