page_title: Lake Nyos
section_title: 1986 disaster
hierarchical_section_title: Lake Nyos / 1986 disaster
caption_attribution_description: English: Combined two photographs to create semi-panoramic view of Lake Nyos. The photos themselves were taken on August 29, 1986, less than a month after the major Limnic eruption. Other version: Image:Tml15-16_Eng.jpg
context_page_description: Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about 315 km northwest of Yaoundé, the capital. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity. A volcanic dam impounds the lake waters.
  A pocket of magma lies beneath the lake and leaks carbon dioxide into the water, changing it into carbonic acid. Nyos is one of only three lakes known to be saturated with carbon dioxide in this way, and therefore prone to limnic eruptions.
  In 1986, possibly as the result of a landslide, Lake Nyos suddenly emitted a large cloud of CO
  2, which suffocated 1,746 people and 3,500 livestock in nearby towns and villages. Though not completely unprecedented, it was the first known large-scale asphyxiation caused by a natural event. To prevent a recurrence, a degassing tube that siphons water from the bottom layers to the top, allowing the carbon dioxide to leak in safe quantities, was installed in 2001. Two additional tubes were installed in 2011.
  Today, the lake also poses a threat because its natural wall is weakening.
context_section_description: Although a sudden outgassing of CO
  2 had occurred at Lake Monoun in 1984, a similar threat from Lake Nyos was not anticipated. However, on August 21, 1986, a limnic eruption occurred at Lake Nyos, triggering the sudden release of about 100,000–300,000 tons (some sources state as much as 1.6 million tonnes) of CO
  2. This gas cloud rose at nearly 100 kilometres per hour (62 mph) and spilled over the northern lip of the lake into a valley running roughly east–west from Cha to Subum. It then rushed down two valleys branching off to the north, displacing all of the air and suffocating 1,746 people within 25 kilometres (16 mi) of the lake, mostly rural villagers, as well as 3,500 livestock. The villages most affected were Cha, Nyos, and Subum.
  Scientists concluded from evidence that a 100 m (330 ft) fountain of water and foam formed at the surface of the lake. The huge amount of water rising suddenly caused much turbulence in the water, spawning a wave of at least 25 metres (82 ft) that would scour the shore of one side.
  It is not known what triggered the catastrophic outgassing. Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake. A third possibility is that cool rainwater falling on one side of the lake triggered the overturn. Others still believe there was a small earthquake, but as witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely. Whatever the cause, the event resulted in the rapid mixing of the supersaturated deep water with the upper layers of the lake, where the reduced pressure allowed the stored CO
  2 to effervesce out of solution.
  It is believed that about 1.2 cubic kilometres (0.29 cu mi) of gas was released. 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.
caption: Lake Nyos as it appeared less than two weeks after the eruption; August 29, 1986.
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