Chemistry:Lake Nyos disaster

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Short description: 1986 limnic eruption in Cameroon

Lake Nyos disaster
Lake Nyos as it appeared eight days after the eruption
Lake Nyos disaster is located in Cameroon
Lake Nyos disaster
Lake Nyos disaster
Date21 August 1986 (1986-08-21)
LocationCameroon
Coordinates [ ⚑ ] : 6°26′N 10°18′E / 6.44°N 10.30°E / 6.44; 10.30
TypeLimnic eruption
Deaths1,746
Non-fatal injuries845

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

The eruption triggered the sudden release of about 100,000–300,000 tons of carbon dioxide (CO2).[2][3] The gas cloud initially rose at nearly 100 kilometres per hour (62 mph; 28 m/s) and then, being heavier than air, descended onto nearby villages, suffocating people and livestock within 25 kilometres (16 mi) of the lake.[4][5]

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. Along with the Lake Monoun disaster two years earlier, it is one of only two recorded limnic eruptions in history.[6]

Eruption and gas release

What triggered the catastrophic outgassing is not known.[7][8][9] Most geologists suspect a landslide, but some believe that a small volcanic eruption may have occurred on the bed of the lake.[10][11] A third possibility is that cool rainwater falling on one side of the lake triggered the overturn. Other scientists offer that no external action is needed to start this event. “The horizontal layering of the water column is due to the differential diffusion of CO2 and heat but, contrary to salt (which stabilises the thermohaline stratification of the oceans), carbon dioxide has a solubility that is limited by temperature, making the stratification intrinsically unstable. Thus, there is even no need of an external trigger (landslide, earthquake or heavy rain) to upset the stratification 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.”[12]

The event resulted in the supersaturated deep water rapidly mixing with the upper layers of the lake, where the reduced pressure allowed the stored CO
2 to effervesce out of solution.[13]

It is believed that about 1.2 cubic kilometres (4.2×1010 cu ft) of gas was released.[14] 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[15] and trees near the lake were knocked down.[16]

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.[17]

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; 5.6–13.9 m/s). 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.[4] About 4,000 inhabitants fled the area, and many of these developed respiratory problems, lesions, and paralysis as a result of the gas cloud.[18]

It is a possibility that other volcanic gases were released along with the CO
2, 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, CO
2 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.[18]

Effects on survivors

Cattle suffocated by carbon dioxide from Lake Nyos

Reporters in the area described the scene as "looking like the aftermath of a neutron bomb."[19] One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:[4][20]

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 morning (of Friday, the next day) ... 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 (the same day). (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.

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 sulphur-based gases. Poisoning by these gases would lead to burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled.[9]

Interviews with survivors and pathologic studies indicated that victims rapidly lost consciousness and that death was caused by CO
2 asphyxiation.[21] At nonlethal levels, CO
2 can produce sensory hallucinations, such that many people exposed to CO
2 report the odor of sulfuric compounds when none are present.[21] 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.[21]

Degassing

The scale of the disaster led to studies on how a recurrence could be prevented.[22] Several researchers proposed the installation of degassing columns from rafts in the middle of the lake.[23][24] 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.[12][25]

Starting from 1995, feasibility studies were successfully conducted, and the first permanent degassing pipe was installed at the lake in 2001. Two additional pipes were installed in 2011.[16][12][26] 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, without any need for external power.[27]

Similar danger suspected at Lake Kivu

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.[28]

However, a study undertaken in 2018 and released in 2020 found flaws in the 2005 study, including a possible bias in the conversion of concentrations to partial pressures, to an overestimation of concentrations, or to a problem of calibration of sensors at high pressure. 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.[29]

  • 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.[30][31]

See also

References

  1. ↑ Hammond, Trevor (2018-08-01). "Lake Nyos Disaster: August 21, 1986". Fishwrap. https://blog.newspapers.com/lake-nyos-disaster-august-21-1986/. 
  2. ↑ Socolow, Robert H. (July 2005). "Can We Bury Global Warming?". Scientific American 293 (1): 49–55. doi:10.1038/scientificamerican0705-49. ISSN 0036-8733. PMID 16008301. Bibcode: 2005SciAm.293a..49S. https://www.scientificamerican.com/article/can-we-bury-global-warmin/. 
  3. ↑ Mathew Fomine, Forka Leypey (2011). "The Strange Lake Nyos CO2 Gas Disaster". Australasian Journal of Disaster and Trauma Studies 2011-1. ISSN 1174-4707. http://www.massey.ac.nz/~trauma/issues/2011-1/fomine.htm. Retrieved 2016-02-04. 
  4. ↑ 4.0 4.1 4.2 Camp, Vic (2006-03-31). "Lake Nyos (1986)". San Diego State University. http://www.geology.sdsu.edu/how_volcanoes_work/Nyos.html. 
  5. ↑ Smolowe, Jill; Phillips, B. J. (1986-09-08). "Cameroon the Lake of Death". TIME 128 (10): 34–37. http://www.time.com/time/magazine/article/0,9171,962228-1,00.html. Retrieved 2013-12-09. 
  6. ↑ Ohba, Takeshi, et al. "A Depression Containing CO2-Enriched Water at the Bottom of Lake Monoun, Cameroon, and Implications for the 1984 Limnic Eruption." Frontiers in Earth Science, vol. 10, May 2022, p. 766791. DOI.org (Crossref), https://doi.org/10.3389/feart.2022.766791.
  7. ↑ Cotel, Aline J. (March 1999). "A trigger mechanism for the Lake Nyos disaster". Journal of Volcanology and Geothermal Research 88 (4): 343–347. doi:10.1016/s0377-0273(99)00017-7. ISSN 0377-0273. Bibcode: 1999JVGR...88..343C. 
  8. ↑ Rouwet, Dmitri; Tanyileke, Greg; Costa, Antonio (2016-07-12). "Cameroon's Lake Nyos Gas Burst: 30 Years Later". Eos 97. doi:10.1029/2016eo055627. ISSN 0096-3941. https://eos.org/science-updates/cameroons-lake-nyos-gas-burst-30-years-later. Retrieved 18 February 2022. 
  9. ↑ 9.0 9.1 "Hundreds gassed in Cameroon lake disaster". BBC. 1986-08-21. https://news.bbc.co.uk/onthisday/hi/dates/stories/august/21/newsid_3380000/3380803.stm. 
  10. ↑ 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. doi:10.1016/s0377-0273(99)00179-1. ISSN 0377-0273. Bibcode: 2000JVGR...97..233R. https://www.sciencedirect.com/science/article/abs/pii/S0377027399001791. Retrieved 18 February 2022. 
  11. ↑ Aka, Festus Tongwa (2015-03-03). "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 978-3642368325. 
  12. ↑ 12.0 12.1 12.2 Halbwachs, Michel; Grangeon, Jacques; Sabroux, Jean-Christophe; Wong, Brice (c. 2001). "Degassing Lake Nyos project". https://mhalb.pagesperso-orange.fr/nyos/nyos.htm. 
  13. ↑ 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. doi:10.1016/0377-0273(89)90056-5. ISSN 0377-0273. Bibcode: 1989JVGR...39..167K. https://www.sciencedirect.com/science/article/abs/pii/0377027389900565. Retrieved 18 February 2022. 
  14. ↑ Alex (2007-05-21). "The Strangest Disaster of the 20th Century". http://www.neatorama.com/2007/5/21/the-strangest-disaster-of-the-20th-century/. 
  15. ↑ "Gas cloud kills Cameroon villagers" (in en). A&E Television Networks. 2009-11-13. https://www.history.com/this-day-in-history/gas-cloud-kills-cameroon-villagers. 
  16. ↑ 16.0 16.1 Witucki, Mary (2018). DISASTER RISK IN THE LAKE NYOS AREA, CAMEROON: EFFECTS OF THE GAS HAZARD AND SOCIALLY PRODUCED VULNERABILITY (PDF) (Master of Science in Geology thesis). Houghton, Michigan: Michigan Technological University. doi:10.37099/mtu.dc.etdr/758. OCLC 1150782660. S2CID 134744487. ProQuest 13422443. Archived from the original on 2023-12-31. Retrieved 2023-12-31.
  17. ↑ Brown, David (2000-02-01). "Scientists hope to quiet Cameroon's killer lakes". The Seattle Times. The Washington Post. https://archive.seattletimes.com/archive/?date=20000201&slug=4002291. 
  18. ↑ 18.0 18.1 Baxtor, Peter J.; Kapila, M.; Mfonfu, D. (1989-05-27). "Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide?". The BMJ 298 (6685): 1437–1441. doi:10.1136/bmj.298.6685.1437. ISSN 0959-8138. PMID 2502283. PMC 1836556. https://www.bmj.com/content/bmj/298/6685/1437.full.pdf. Retrieved 18 February 2022. 
  19. ↑ DeYoung, Karen (1986-08-27). "Cameroon Toll above 1500". The Washington Post (Yaounde, Cameroon). https://www.washingtonpost.com/wp-dyn/content/article/2006/07/19/AR2006071901345.html?nav=rss_world/africa. 
  20. ↑ A. Scarth. USGS, 1999.
  21. ↑ 21.0 21.1 21.2 Kling, George W.; Clark, Michael A.; Compton, Harry R.; Devine, Joseph D.; Evans, William C.; Humphrey, Alan M.; Koenigsberg, Edward J.; Lockwood, John P. et al. (1987-04-10). "The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa". Science 236 (4798): 169–175. doi:10.1126/science.236.4798.169. PMID 17789781. Bibcode: 1987Sci...236..169K. https://zenodo.org/record/1230976. Retrieved 14 June 2022. 
  22. ↑ Kling, George W.; Evans, William C.; Tanyileke, Greg; Kusakabe, Minoru; Ohba, Takeshi; Yoshida, Yutaka; Hell, Joseph V. (2005-10-04). "Degassing Lakes Nyos and Monoun: Defusing certain disaster". Proceedings of the National Academy of Sciences 102 (40): 14185–14190. doi:10.1073/pnas.0502274102. PMID 16186504. 
  23. ↑ Halbwachs, Michel; Sabroux, Jean-Christophe (2001-04-20). "Removing CO
    2     from Lake Nyos in Cameroon"    . Science 292 (5516): 438. doi:10.1126/science.292.5516.438a. ISSN 0036-8075. PMID 11330293. https://www.science.org/doi/10.1126/science.292.5516.438a. Retrieved 18 February 2022.     
  24. ↑ Schmid, Martin; Halbwachs, Michel; Wüest, Alfred (2006-06-01). "Simulation of CO
    2     concentrations, temperature, and stratification in Lake Nyos for different degassing scenarios"    . Geochemistry, Geophysics, Geosystems 7 (6): 1–14. doi:10.1029/2005GC001164. ISSN 1525-2027. Bibcode: 2006GGG.....7.6019S. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A5288. Retrieved 10 December 2019.     
  25. ↑ "January February 2001 expedition". http://pagesperso-orange.fr/mhalb/nyos/2000/index2000.htm. 
  26. ↑ "Le degazage du lac Nyos". http://www.universcience.fr/fr/science-actualites/film-as/wl/1248122455252/le-degazage-du-lac-nyos/. 
  27. ↑ Halbwachs, Michel; Sabroux, Jean-Christophe; Kayser, Gaston (2020). "Final step of the 32 year Lake Nyos degassing adventure: Natural CO
    2     recharge is to be balanced by discharge through the degassing pipes". Journal of African Earth Sciences 167. doi:10.1016/j.jafrearsci.2019.103575. ISSN 1464-343X. Bibcode: 2020JAfES.16703575H.     
  28. ↑ Schmid, Martin; Halbwachs, Michel; Wehrli, Bernhard; Wüest, Alfred (July 2005). "Weak mixing in Lake Kivu: New insights indicate increasing risk of uncontrolled gas eruption". Geochemistry, Geophysics, Geosystems 6 (7): Q07009. doi:10.1029/2004GC000892. Bibcode: 2005GGG.....6.7009S. https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A5020. Retrieved 14 June 2022. 
  29. ↑ Bärenbold, Fabian; Boehrer, Bertram; Grilli, Roberto; Mugisha, Ange; von Tümpling, Wolf; Umutoni, Augusta; Schmid, Martin (25 August 2020). "No Increasing Risk of a Limnic Eruption at Lake Kivu: Intercomparison Study Reveals Gas Concentrations Close to Steady State". PLoS One 15 (8): 11. doi:10.1371/journal.pone.0237836. PMID 32841245. Bibcode: 2020PLoSO..1537836B. 
  30. ↑ "Water Into Blood?". Biblical Archaeology Society. https://library.biblicalarchaeology.org/images/bsba320606203ljpg/. 
  31. ↑ Sivertsen, Barbara J. (2009). "The Minoan Eruption". The Parting of the Sea: How Volcanoes, Earthquakes, and Plagues Shaped the Story of the Exodus. Princeton University Press. p. 25. ISBN 978-0-691-13770-4. 



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