Lake Nyos disaster

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

Lake Nyos disaster
Lake Nyos as it appeared eight days after the eruption
Date21 August 1986 (1986-08-21)
LocationCameroon
Coordinates6.437698°N 10.297975°E / 6.437698; 10.297975
TypeLimnic eruption
Deaths1,746

The eruption triggered the sudden release of about 100,000–300,000 tons (1.6 million tons, according to some sources) of carbon dioxide (CO
2).[1][2] The gas cloud initially rose at nearly 100 kilometres per hour (62 mph) and then, being heavier than air, descended onto nearby villages, displacing all the air and suffocating people and livestock within 25 kilometres (16 mi) of the lake.[3][4]

A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO
2 in the waters and therefore the risk of further eruptions.

Eruption and gas cloud

It is not known what triggered the catastrophic outgassing.[5][6][7] Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake.[8][9] 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 because witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely. 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.[10]

It is believed that about 1.2 cubic kilometres (0.29 cu mi) of gas was released.[11] 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 m (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.[12]

Since carbon dioxide is 1.5 times the density of air, the cloud hugged the ground and moved down the valleys, where there were various villages. The mass was about 50 metres (160 ft) thick, and travelled downward at 20–50 kilometres per hour (12–31 mph). 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.[3] About 4,000 inhabitants fled the area, and many of these developed respiratory problems, lesions, and paralysis as a result of the gas cloud.[13]

It is a possibility that other volcanic gases were released along with the CO2, as some survivors reported a smell of gunpowder or rotten eggs which indicates that sulfur dioxide and hydrogen sulfide were present at concentrations above their odour thresholds. 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.[13]

Effects on survivors
Cattle suffocated by carbon dioxide from Lake Nyos

One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:

"I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible ... I heard my daughter snoring in a terrible way, very abnormal ... When crossing to my daughter's bed ... I collapsed and fell. I was there till nine o'clock in the (Friday) morning ... until a friend of mine came and knocked at my door ... I was surprised to see that my trousers were red, had some stains like honey. I saw some ... starchy mess on my body. My arms had some wounds ... I didn't really know how I got these wounds ... I opened the door ... I wanted to speak, my breath would not come out ... My daughter was already dead ... I went into my daughter's bed, thinking that she was still sleeping. I slept till it was 4.30 in the afternoon ... on Friday. (Then) I managed to go over to my neighbours' houses. They were all dead ... I decided to leave ... (because) most of my family was in Wum ... I got my motorcycle ... A friend whose father had died left with me (for) Wum ... As I rode ... through Nyos I didn't see any sign of any living thing ... (When I got to Wum), I was unable to walk, even to talk ... my body was completely weak."[3][14]

Following the eruption, many survivors were treated at the main hospital in Yaoundé, the country's capital. It was believed that many of the victims had been poisoned by a mixture of gases that included hydrogen and sulfur. Poisoning by these gases would lead to burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled.[7]

Interviews with survivors and pathologic studies indicated that victims rapidly lost consciousness and that death was caused by CO2 asphyxiation. [15] At nonlethal levels, CO2 can produce sensory hallucinations, such that many people exposed to CO2 report the odor of sulfuric compounds when none are present. [15] Skin lesions found on survivors represent pressure sores, and in a few cases exposure to a heat source, but there is no evidence of chemical burns or of flash burns from exposure to hot gases. [15]

Aftermath

The scale of the disaster led to much study on how a recurrence could be prevented.[16] Several researchers proposed the installation of degassing columns from rafts in the middle of the lake.[17][18] The principle is to slowly vent the CO
2 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.[19]

Starting from 1995, feasibility studies were successfully conducted, and the first permanent degassing tube was installed at Lake Nyos in 2001. Two additional pipes were installed in 2011.[20][21] In 2019 it was determined that the degassing had reached an essentially steady state and that a single one of the installed pipes would be able to self-sustain the degassing process into the future, indefinitely maintaining the CO
2 at a safe level of without any need for external power.[22]

Following the Lake Nyos disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. Lake Kivu in the Democratic Republic of 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 Greek novel by Basileios Drolias focusing on the Lake Nyos disaster and the degassing of the lake was published in 2016.[23]

See also

References
  1. Socolow, Robert H. (July 2018). "Can We Bury Global Warming? (2005)". Scientific American. 293 (1): 49–55. doi:10.1038/scientificamerican0705-49. PMID 16008301.
  2. Mathew Fomine, Forka Leypey (2011). "The Strange Lake Nyos CO2 Gas Disaster". Australasian Journal of Disaster and Trauma Studies. 2011–1. ISSN 1174-4707. Retrieved February 4, 2016.
  3. "Lake Nyos (1986)". San Diego State University. March 31, 2006. Retrieved December 19, 2008.
  4. Smolowe, Jill (September 8, 1986). "Cameroon the Lake of Death". TIME. 128 (10): 34–37. Archived from the original on February 27, 2009. Retrieved December 9, 2013.
  5. Cotel, Aline J (March 1999). "A Trigger Mechanism for the Lake Nyos Disaster". Journal of Volcanology and Geothermal Research. 88 (4): 343–347. Bibcode:1999JVGR...88..343C. doi:10.1016/s0377-0273(99)00017-7.
  6. Rouwet, Dmitri; Tanyileke, Greg; Costa, Antonio (July 12, 2016). "Cameroon's Lake Nyos Gas Burst: 30 Years Later". Eos. 97. doi:10.1029/2016eo055627.
  7. BBC contributors (August 21, 1986). "21 August: 1986: Hundreds gassed in Cameroon lake disaster". BBC. Retrieved December 19, 2008.
  8. Rice, A (April 2000). "Rollover in Volcanic Crater Lakes: A Possible Cause for Lake Nyos Type Disasters". Journal of Volcanology and Geothermal Research. 97 (1–4): 233–239. Bibcode:2000JVGR...97..233R. doi:10.1016/s0377-0273(99)00179-1.
  9. Aka, FestusTongwa (2015). "Depth of Melt Segregation Below the Nyos Maar-Diatreme Volcano (Cameroon, West Africa): Major-Trace Element Evidence and Their Bearing on the Origin of CO2 in Lake Nyos". Volcanic Lakes. Advances in Volcanology. Springer Berlin Heidelberg. pp. 467–488. doi:10.1007/978-3-642-36833-2_21. ISBN 9783642368325.
  10. Kusakabe, Minoru; Ohsumi, Takashi; Aramaki, Shigeo (November 1989). "The Lake Nyos Gas Disaster: Chemical and Isotopic Evidence in Waters and Dissolved Gases from Three Cameroonian Crater Lakes, Nyos, Monoun and Wum". Journal of Volcanology and Geothermal Research. 39 (2–3): 167–185. Bibcode:1989JVGR...39..167K. doi:10.1016/0377-0273(89)90056-5.
  11. "The Strangest Disaster of the 20th Century". Neatorama. May 21, 2007. Archived from the original on September 29, 2011. Retrieved June 20, 2010.
  12. David Brown (February 1, 2000). "Scientists hope to quiet Cameroon's killer lakes". The Washington Post. Retrieved December 19, 2008.
  13. Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide?, BMJ, Volume 298, May 27, 1989,
  14. A. Scarth. USGS, 1999.
  15. Kling, George; Clark, Michael; Compton, Harry; Devine, Joseph; Evans, Williams; Humphrey, Alan; Koenigsberg, Edward; Lockwood, John; Tuttle, Michele; Wagner, Glen (10 April 1987). "The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa". Science. 236 (4798): 169–175.
  16. Kling, G. W.; Evans, W. C.; Tanyileke, G.; Kusakabe, M.; Ohba, T.; Yoshida, Y.; Hell, J. V. (2005). "Degassing Lakes Nyos and Monoun: Defusing certain disaster". Proceedings of the National Academy of Sciences. 102 (40): 14185–90. doi:10.1073/pnas.0502274102. PMC 1242283. PMID 16186504.
  17. Halbwachs, Michel; Sabroux, Jean-Christophe (20 April 2001). "Removing CO2 from Lake Nyos in Cameroon". Science. 292 (5516): 438. doi:10.1126/science.292.5516.438a. ISSN 0036-8075. PMID 11330293.
  18. Schmid, Martin; Halbwachs, Michel; Wüest, Alfred (1 June 2006). "Simulation of CO2 Concentrations, Temperature, and Stratification in Lake Nyos for Different Degassing Scenarios". Geochemistry, Geophysics, Geosystems. 7 (6): n/a. Bibcode:2006GGG.....7.6019S. doi:10.1029/2005GC001164. ISSN 1525-2027.
  19. Degassing Lake Nyos project http://pagesperso-orange.fr/mhalb/nyos/nyos.htm
  20. "Degassing the "Killer Lakes" Expedition 2001". pagesperso-orange.fr. Archived from the original on 2009-02-06. Retrieved 2016-08-22.
  21. "Science Actualités – Ressources – Cité des sciences et de l'industrie – Expositions, conférences, cinémas, activités culturelles et sorties touristiques pour les enfants, les parents, les familles – Paris". Universcience.fr. Archived from the original on January 3, 2012. Retrieved October 17, 2012.
  22. Halbwachs, Michel; Sabroux, Jean-Christophe; Kayser, Gaston (2020). "Final step of the 32-year Lake Nyos degassing adventure: Natural CO2 recharge is to be balanced by discharge through the degassing pipes". Journal of African Earth Sciences. 167: 103575. doi:10.1016/j.jafrearsci.2019.103575. ISSN 1464-343X.
  23. Drolias, Basileios (2016). "Nyos". Kedros. OCLC 971991694. Cite journal requires |journal= (help)
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