Limnic Eruptions: When Lakes Become Deadly

Limnic Eruptions: When Lakes Become Deadly

 

A limnic eruption is defined as "a rare type of natural disaster in which dissolved carbon dioxide suddenly erupts from deep lake waters, forming a gas cloud capable of suffocating wildlife, livestock, and humans." Also known as a lake overturn, it can happen quickly, unexpectedly, and with severe consequences to any living things in the surrounding area.

Certain factors need to be in place for a limnic eruption to occur: It is thought that these eruptions are generally triggered by seismic activity. Disruptions in the Earth's crust can cause underground shifts, triggering the explosions or releasing pressure in the area. This phenomenon, in turn, is thought to lead to the initial disruption that causes the eruption.

Lake Nyos, the site of a limnic eruption in 1986

The Science Behind Limnic Eruptions: A Delicate Balance

Understanding the delicate balance that leads to a limnic eruption requires delving into three key areas:

1. Necessary Ingredients:

Source of CO2: 

Volcanic activity is a common source, as volcanic gases like CO2 can seep into nearby lakes.

Meromictic Lake: 

Most lakes are holomictic, meaning their water mixes regularly. Limnic eruptions require a meromictic lake, where deep layers don't mix with the upper water due to temperature and density differences. This allows CO2 to accumulate in the depths.

Depth: 

The lake needs to be deep enough to hold a significant volume of water under high pressure. This pressure allows more CO2 to dissolve in the bottom layer.

2.     Triggering the Eruption:

While the exact cause remains under investigation, several events are believed to disrupt the lake's stratification, triggering the eruption:

Earthquakes: 

Seismic activity can stir up the layers, causing CO2-rich water to rise.

Volcanic Activity: Volcanic eruptions can inject fresh CO2 directly into the lake or destabilize the water column.

Landslides:

Large landslides can disrupt the lake's stability, triggering an overturn event.

3. The CO2 Release Process:

When a trigger event disrupts the lake's stratification, the CO2-rich bottom layer mixes with the upper, less pressurized water. This sudden pressure drop causes the CO2 to rapidly come out of solution, forming bubbles that rise to the surface. The eruption can expel millions of tons of CO2 into the atmosphere in a short period.

 

4. The Devastating Impact of Limnic Eruptions: A Silent Killer

Limnic eruptions, while rare, unleash a silent killer – carbon dioxide (CO2) – that can have a catastrophic impact on the surrounding environment and its inhabitants. Let's delve into the two main ways limnic eruptions cause widespread devastation:

 

1.      CO2 Asphyxiation:

Invisible Threat: CO2 is a colorless and odorless gas, making it difficult to detect during an eruption.

Denser Than Air: CO2 is denser than air, causing it to hug the ground and flow into valleys, suffocating people and animals on the shore and even miles away.

Silent Killer: Victims don't experience the burning sensation typical of smoke inhalation. Instead, they experience rapid unconsciousness and death due to oxygen deprivation.

2.      Physical Dangers:

Tsunamis and Seiches: The rapid rise of CO2 can displace a massive amount of water, creating waves that can travel like tsunamis, flooding low-lying areas and causing structural damage.

Ecological Disruption: The sudden release of CO2 can acidify the lake water, harming or killing aquatic life. The eruption itself can also stir up bottom sediments, creating further ecological disruption.

 

5. Beyond the immediate loss of life, limnic eruptions can have long-lasting consequences:

Food Security: The death of fish and livestock can disrupt food sources for nearby communities.

Water Contamination: Acidified lake water may become unfit for drinking or irrigation.

Psychological Trauma: The sudden and unexpected nature of these eruptions can leave survivors with long-term psychological trauma.

Understanding the impact of limnic eruptions is crucial for raising awareness and developing mitigation strategies in high-risk areas.

 

6. Case Studies of Limnic Eruptions: A Tale of Two Lakes

Limnic eruptions are rare, but their impact can be devastating. Here's a closer look at two of the most well-documented cases:

1. Lake Monoun Eruption (1984): A Deadly Awakening

Location: Lake Monoun, Cameroon, West Africa

Date: August 15, 1984

Estimated CO2 Release: 30-40 million cubic meters (m³)

Casualties: 37 people

The first recorded limnic eruption occurred at Lake Monoun.  The eruption released a large amount of CO2,  though less significant compared to Lake Nyos. The colorless and odorless gas descended the slopes surrounding the lake, suffocating people in nearby villages. The cause of the eruption remains unclear, with possibilities ranging from a landslide to a small volcanic event at the lake bottom. This event served as a wake-up call to the scientific community, highlighting the dangers posed by limnic eruptions.

 

2. Lake Nyos Disaster (1986): A Tragedy of Immense Proportions

Location: Lake Nyos, Cameroon, West Africa (around 160 km from Lake Monoun)

Date: August 21, 1986

Estimated CO2 Release: 100-300 million metric tons (1.2 billion cubic meters)

Casualties: Over 1,700 people and thousands of livestock

Just two years after Lake Monoun, the world witnessed the deadliest limnic eruption at Lake Nyos. The eruption released a colossal amount of CO2, forming a gas cloud that suffocated people and animals within a 25 km radius. The trigger for this eruption is still debated, with possibilities including a landslide or even sudden changes in air pressure and lake temperature. The Lake Nyos disaster highlighted the need for mitigation strategies in areas with high-risk lakes.

Upoma Das

          Executive Member of 'Nature's Pulse'

          Bachelor of Science in Disaster Management

         Faculty of 'Life and Earth Science'

        Begum Rokeya University, Rangpur