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Lake Nyos is a crater lake that is situated in Cameroon’s northwestern region some 196 miles from the capital city of Yaoundé. The lake lies on the Oku volcanic plain next to an inactive volcano, which, in turn, is on top of the nation’s line of volcanic activity. The deep lake has an average depth of about 311 feet and a maximum depth of around 682 feet. Underneath it, there are magma pockets that occasionally leak carbon dioxide into the water, resulting in a high acidity level in the lake.
When the Lake Nyos disaster happened on August 21, 1986, it caused the death of 1,746 humans and 3,500 livestock. The disaster was caused by a limnic eruption, a rare type of eruption that happens when dissolved carbon dioxide in water erupts as a deadly cloud that can suffocate living things. Another name for a limnic eruption is a lake overturn. Since the disaster, a degassing system has been set up in order to reduce the concentration of carbon dioxide in the lake.
To this day, three decades later, scientists are still not sure of the exact cause of the deadly eruption of that fateful day. Some experts attribute the cause to a landslide, others stick to a small volcanic eruption on the lake’s bed, and others theorize the cause as cool rainwater. Those who argued that it was an earthquake have long since changed their theories since there were no tremors detected. In addition, none of the witnesses reported a tremor.
As stated before, the water is extremely saturated with carbon dioxide from the magma pocket below. The deeper waters of the lake are more saturated than the top layers. The vicious explosion happened because there was a rapid mixing of water from the bottom and the top, which meant an equally quick change of pressure. Consequently, the changes in pressure caused an effervescence that brought about the cloud.
Experts are not sure but the effervesced carbon dioxide could have been anywhere between 100,000 and 300,000 tons. Some sources go so much as to estimate a whopping 1.6 million tons. The water from the lakebed, which is rich in iron, was rapidly oxidized as it came to the surface thus changing the water from the normal blue to a deep red. In addition, the water level dropped by about a meter.
Once the cloud mass was formed, it rose up for a bit before descending into the nearby villages. The mass, which has a thickness of about 160 feet, descended because carbon dioxide is about 1.5 times denser than air. Once it reached the villages, it displaced the air and suffocated plenty of people in their sleep, especially within a radius of about 14 miles. Some of the villages within the radius included Nyos, Subum, Cha, and Kam. About 4,000 people fled but many of those developed health conditions such as lesions and paralysis.
Possibility of Other Gases
As the lake was on top of a magma pocket, it is possible that other gases were released as well. Knowledge of volcanic eruptions shows that, aside from carbon dioxide, other gases released may include water vapor and sulfides. Indeed, some of the survivors reported a smell like rotten eggs, which is an indicator of either sulfur dioxide or hydrogen sulfide or both. Any water vapor would have mixed with the water to form an acidic mixture that may have added to the damage. However, carbon dioxide was the dominant gas.
Effects and Aftermath
A dark cloud hung over the villages months after the horrific event. An account of one survivor named Joseph Nkwain outlines the horrific events of the day. Joseph narrated that he heard his daughter snoring in an abnormal manner before her death. On his way to her bed, he collapsed only for a friend to wake him up later. He woke up to see wounds on his arms and red stains on his trousers. While leaving the village later on a motorcycle, he saw no sign of any living thing. Joseph and many other survivors were seen to at a hospital in Yaoundé. Most of the victims suffered extra poisoning that further supported the presence of sulfur and hydrogen.
Authorities acted on the matter soon after in order to prevent a similar disaster, which is where the idea for degassing columns arose. The idea behind degassing columns is to lift saturated water from the lake bed slowly in order to release gas safely. The first column was installed in 2001 followed by two more in 2011.
There are other lakes in Africa that are similar to Lake Nyos, such as the DRC’s Lake Kivu, which is considerably bigger (about 2,000 times bigger) than Lake Nyos. In order to check if similar happenings could occur, experts studied Lake Kivu. They found that similar events happened around the lake every millennium.