DiscoverScroll article

On 21 August 1986, a limnic eruption at Lake Nyos in northwestern Cameroon killed 1,746 people and 3,500 livestock.

The eruption triggered the sudden release of about 100,000–300,000 tons of carbon dioxide (CO2). The gas cloud initially rose at nearly 100 km/h (62 mph; 28 m/s) and then, being heavier than air, descended onto nearby villages, suffocating people and livestock within 25 km (16 miles) of the lake. A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in the waters and therefore the risk of further eruptions. Along with the Lake Monoun disaster two years earlier, it is one of only two recorded limnic eruptions in modern human history.

Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake. Once CO2 bubbles nucleate within a saturated layer of the lake water, they rise and grow, attracting in their wake deeper water available for ex-solution, feeding the chain reaction process : the entire lake overturns through an ascending column of rising and expanding bubbles. The event resulted in the supersaturated deep water rapidly mixing with the upper layers of the lake, where the reduced pressure allowed the stored CO2 to effervesce out of solution. The normally blue waters of the lake turned a deep red after the outgassing, due to iron‑rich water from the deep rising to the surface and being oxidised by the air. The level of the lake dropped by about a metre and trees near the lake were knocked down. Scientists concluded from evidence that a 100 metres (330 ft) column of water and foam formed at the surface of the lake, spawning a wave of at least 25 metres (82 ft) that swept the shore on one side. For roughly 23 kilometres (14 mi), the gas cloud was concentrated enough to suffocate many people in their sleep in the villages of Nyos, Kam, Cha, and Subum. However, CO2 was the only gas detected in samples of lake water, suggesting that this was the predominant gas released and as such the main cause of the incident.

The principle is to slowly vent the CO2 by lifting heavily saturated water from the bottom of the lake through a pipe, initially by using a pump, but only until the release of gas inside the pipe naturally lifts the column of effervescing water, making the process self-sustaining. Starting from 1995, feasibility studies were successfully conducted, and the first permanent degassing pipe was installed at the lake in 2001.

Following the Lake Nyos disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. In 2005, Lake Kivu in the Democratic Republic of the Congo, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence that outgassing events around the lake happened about every thousand years. The 2020 study found that when these errors were accounted for, the risk of a gas eruption at Lake Kivu did not seem to be increasing over time.

In The Exodus Decoded (2006), journalist Simcha Jacobovici references the Lake Nyos disaster to explain how the Biblical plagues (such as the Nile River turning into "blood", mass death of livestock, the outbreak of boils and death of the firstborn) occurred due to the Minoan eruption at Santorini circa 1600 BCE. Jacobovici proposed that the Exodus may have coincided with the eruption of Santorini, arguing that seismic activity could have contributed to events described in the biblical narrative, including the plagues and the parting of the Red Sea. Jacobovici also suggested that the biblical Red Sea may have referred to a freshwater lake near modern-day Ismailia.

Quick Facts

• In 2005, Lake Kivu in the Democratic Republic of the Congo, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence that outgassing events around the lake happened about every thousand years.
• A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in the waters and therefore the risk of further eruptions.
• The gas cloud initially rose at nearly 100 km/h (62 mph; 28 m/s) and then, being heavier than air, descended onto nearby villages, suffocating people and livestock within 25 km (16 miles) of the lake.
• Along with the Lake Monoun disaster two years earlier, it is one of only two recorded limnic eruptions in modern human history.
• Following the Lake Nyos disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere.

Source material: Wikipedia - "Lake Nyos disaster". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.