Lake Nyos 238025 225202776 2008-07-12T13:00:07Z Tomtefarbror 696780 restore original correct coordinates by Autodidactyl (6.44° N 10.30° E) {{Infobox lake | lake_name = Lake Nyos | image_lake = Lake_nyos_local.jpg | caption_lake = | image_bathymetry = | caption_bathymetry= | location = [[Northwest Province, Cameroon|Northwest Province]] | coords = {{coor at d|6.44|N|10.30|E|type:waterbody_region:CM}} | type = [[Meromictic]], [[crater lake]] | inflow = ''subaquatic source'' | outflow = | catchment = | basin_countries = Cameroon | length = {{convert|2.0|km|mi|abbr=on|lk=on}} | width = {{convert|1.2|km|mi|abbr=on|lk=on}} | area = {{convert|1.58|km2|acre|abbr=on|lk=on}} | depth = | max-depth = {{convert|208|m|ft|abbr=on|lk=on}} | volume = {{convert|0.15|km3|acre.ft|abbr=on|lk=on}} | residence_time = | shore = | elevation = {{convert|1091|m|ft|abbr=on|lk=on}} | islands = | cities = | frozen = }} '''Lake Nyos''' is a [[crater lake]] in the [[Northwest Province, Cameroon|Northwest Province]] of [[Cameroon]]. 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 natural [[dam]] of [[volcanic rock]] hems in the lake waters. A pocket of [[magma]] lies beneath the lake and leaks [[carbon dioxide]] (CO<sub>2</sub>) into the water, changing it into [[carbonic acid]]. Nyos is one of only three known lakes to be saturated with carbon dioxide in this way, the others being [[Lake Monoun]], at a distance of 100 km SSE, and [[Lake Kivu]] in [[Rwanda]]. On [[21 August]] [[1986]], possibly triggered by a landslide, the lake suddenly emitted a large cloud of CO<sub>2</sub>, which [[Asphyxia|suffocated]] 1,700 people and 3,500 livestock in nearby villages.<ref>New York Times, "Trying to Tame the Roar of Deadly Lakes", February 27, 2001. [http://query.nytimes.com/gst/fullpage.html?res=9F04E2DC1F39F934A15751C0A9679C8B63&sec=&spon=&partner=permalink&exprod=permalink].</ref> Though not completely unprecedented, it was the first known large-scale asphyxiation caused by a natural event. To prevent a repetition, a degassing tube that syphons water from the bottom layers of water to the top allowing the carbon dioxide to leak in safe quantities was installed in 2001, though additional tubes are needed to make the lake safe.<ref>Degassing Lakes Nyos and Monoun: Defusing certain disaster, Proceedings of the National Academy of the Sciences, October 4, 2005, vol. 102, no. 40, 14185-14190</ref> Today, the lake also poses a threat due to its weakening natural wall. A geological tremor could cause this [[Dike (construction)|dike]] to give way, allowing water to rush into downstream villages all the way into [[Nigeria]]. ==Formation and geological history== Lake Nyos is a couple of kilometres south of the dirt road from [[Wum]], about 30 km to the west, to Nkambe in the east. Villages along the road in the vicinity of the lake include Cha, Nyos, Munji, Djingbe, and Subum. The lake is 50 km from the Nigerian border to the north, and lies on the northern slopes of the Massif du Mbam, drained by streams running north then north-west to the Katsina-Ala River in Nigeria, part of the [[Benue River]] basin.<ref>[http://encarta.msn.com/encnet/features/mapcenter/map.aspx?TextLatitude=-0.336785200454403&TextLongitude=29.5037588339211&TextAltitude=6&TextSelectedEntity=1075&MapStyle=Comprehensive&MapSize=Large&MapStyleSelectedIndex=0&searchTextMap=Wum&MapStylesList=Comprehensive&ZoomOnMapClickCheck=on "Map of Wum, Cameroon".] ''MSN Encarta World Atlas''.</ref> Lake Nyos fills a roughly circular [[maar]] in the [[Oku Volcanic Field]], an explosion crater caused when a [[lava flow]] interacted violently with [[groundwater]]. The maar is believed to have formed in an eruption about 400 years ago, and is 1,800 m (5,900 ft) across and 208 m (682 ft) deep<ref>Smithsonian Institution Global Volcanism Program Website, 1999</ref>. The area has been volcanically active for millions of years — after [[South America]] and [[Africa]] were split apart by [[plate tectonics]] about 110 million years ago, [[West Africa]] also experienced rifting, although to a lesser degree. The rift is known as the [[Mbéré Rift Valley]], and [[crust (geology)|crust]]al extension has allowed [[magma]] to reach the surface along a line extending through Cameroon. [[Mount Cameroon]] also lies on this fault line. Lake Nyos is surrounded by old lava flows and [[pyroclastic flow|pyroclastic]] deposits. The lake waters are held in place by a natural [[dam]] composed of [[volcanic rock]]. At its narrowest point, the wall measures 40 metres high and 45 metres wide. ==Gas saturation== Lake Nyos is one of only three lakes in the world known to be saturated with carbon dioxide&mdash;the others are [[Lake Monoun]], also in Cameroon about 100 km away, and [[Lake Kivu]] in [[Rwanda]]. A [[magma chamber]] beneath the region is an abundant source of carbon dioxide, which seeps up through the lake bed, charging the waters of Lake Nyos with an estimated 90 million [[tonne]]s of CO<sub>2</sub>. Lake Nyos is thermally stratified, with layers of warm, less dense water near the surface floating on the colder, denser water layers near the lake's bottom. Over long periods, carbon dioxide gas seeping into the cold water at the lake's bottom is dissolved in great amounts. Most of the time, the lake is stable and the CO<sub>2</sub> remains in solution in the lower layers. However, over time the water becomes [[supersaturation|supersaturated]], and if an event such as an [[earthquake]] or [[volcanic eruption]] occurs, large amounts of CO<sub>2</sub> may suddenly come out of solution. ==The 1986 disaster== [[Image:Tml15-16 Nc.jpg|thumb|300 px|Lake Nyos as it appeared less than two weeks after the eruption; August 29, 1986. Areas once covered with vegetation are especially visible from the divide between photos to the extreme right.]] [[Image:Cow killed by Lake Nyos gasses.jpg|thumb|left|150px|A cow suffocated by gases from Lake Nyos]] Although a sudden outgassing of CO<sub>2</sub> had occurred at [[Lake Monoun]] in 1984, killing 37 local residents, a similar threat from Lake Nyos was not anticipated. However, on [[August 21]], [[1986]], a [[limnic eruption]] occurred at Lake Nyos which triggered the sudden release of about 1.6 million [[tonne]]s of CO<sub>2</sub>. The gas spilled over the northern lip of the lake into a valley running roughly east-west from Cha to Subum, and then rushed down two valleys branching off it to the north, displacing all the air and suffocating some 1,700 people within 20&nbsp;km of the lake, mostly rural villagers, as well as 3,500 livestock. Worst affected villages were Cha, Nyos, and Subum.<ref>[http://www.time.com/time/magazine/article/0,9171,962228-1,00.html Jill Smolowe: "Cameroon the Lake of Death".] ''Time'' Magazine, Monday, Sep. 08, 1986.</ref> About 4,000 inhabitants fled the area, and many of these developed respiratory problems, lesions, and paralysis as a result of the gases.<ref>Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide?, BMJ, Volume 298, 27 May 1989, [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1836556]</ref> 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. 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<sub>2</sub> to [[effervescence|effervesce]] out of solution. It is believed that up to a [[cubic kilometre]] of gas was released. Because pure CO<sub>2</sub> is denser than [[air]], the gas flowed off the mountainous flank in which Lake Nyos rests and down two adjoining valleys in a layer tens of metres deep, displacing the air and suffocating all the people and animals before it could dissipate. 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 [[oxidise]]d by the air. The level of the lake dropped by about a metre, representing the volume of gas released. The outgassing probably also caused an overflow of the waters of the lake. Trees near the lake were knocked down. === Degassing === [[Image:limnic degassing1.jpg|thumb|right|300px|[[France|French]] scientists working on degassing Lake Nyos.]] The scale of the disaster led to much study on how a recurrence could be prevented. Estimates of the rate of carbon dioxide entering the lake suggested that outgassings could occur every 10-30 years, though a recent study shows that release of water from the lake, caused by erosion of the natural barrier that keeps in the lake's water, could in turn reduce pressure on the lake's carbon dioxide and cause a gas escape much sooner. Several researchers independently proposed the installation of degassing columns from rafts in the lake. The principle is simple: a pump lifts water from the bottom of the lake, heavily saturated with CO<small><sub>2</sub></small>, until the loss of pressure begins releasing the gas from the [[diphasic fluid]] and thus makes the process self-powered.<ref> Degassing Lake Nyos project http://pagesperso-orange.fr/mhalb/nyos/nyos.htm</ref> In 1992 at Monoun, and in 1995 at Nyos, a French team demonstrated the feasibility of this approach. In 2001, the US [[Office of Foreign Disaster Assistance]] funded a permanent installation at Nyos.<ref>[http://pagesperso-orange.fr/mhalb/nyos/2000/index2000.htm Degassing the "Killer Lakes" Expedition 2001<!-- Bot generated title -->]</ref> More pipes are expected to be needed to make the lake safe: the original French estimates called for a total of five, and the current OFDA project calls for an additional two pipes, each with ten times the capacity of the single current pipe. Following the Lake Nyos tragedy, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. [[Lake Kivu]] in [[Rwanda]], 2,000 times larger than Lake Nyos, was found also to be supersaturated, and geologists found evidence for outgassing events around the lake about every thousand years. The eruption of nearby [[Mount Nyiragongo]] in 2002 sent [[lava]] flowing into the lake, raising fears that a gas eruption could be triggered, but fortunately it was not, as the flow of lava stopped well before it got near the bottom layers of the lake where the gas is. ==Weakening dam== On [[18 August]], [[2005]], Dr. Isaac Njilah, a geologist at the [[University of Yaoundé]], suggested that the natural [[dam]] of [[volcanic rock]] that keeps in the lake's waters could collapse in the near future. [[Erosion]] has worn the dam away, causing holes and pockets to develop in the dam's upper layer, and water already passes through the lower section. Meanwhile, landslides have reduced dam strength on the outside. Seismic activity caused by the lake's volcanic foundation could thus cause the lake wall to give way, resulting in up to 50 million cubic metres of water flooding downhill into areas of the Northwest Province and the [[Nigeria]]n states of [[Taraba]] and [[Benue]]. Dr. Njilah estimates that the area is home to more than 10,000 people. The Cameroonian government, speaking through Dr. Gregory Tanyi-Leke of the [[Institute of Mining and Geological Research]], acknowledges the weakening wall but denies that it presents any immediate threat. A [[United Nations]] team led by Olaf Van Duin and Nisa Nurmohamed of the [[Netherlands]] Ministry of Transport and Public Works inspected the dam over three days in September 2005 and confirmed that the natural lip had weakened. Van Duin believes that the dam will breach in the next 10 or 20 years. One possible means of averting such a catastrophe would be to strengthen the lake wall, though this would take much time and money. Engineers could also introduce a channel to allow excess water to drain; if the water level were lowered by about 20 metres, the pressure on the wall would be reduced significantly. ==See also== *[[Limnic eruption]] *[[Mazuku]] *[[Meromictic Lakes]] *[[Henry's Law]] *[[Raoult's Law]] *[[Lake Monoun]] *[[Lake Kivu]] *[[Disasters]] ==References== {{reflist}} *{{VNUM|1=0204-03-|2=Oku Volcanic Field}} *[http://za.today.reuters.com/news/newsArticle.aspx?type=topNews&storyID=2005-08-23T160411Z_01_BAN357745_RTRIDST_0_OZATP-CAMEROON-DAM-20050823.XML "Cameroon scientist denies dam about to collapse"] (23 August 2005). Reuters. *Cotel A (1999), ''A trigger mechanism for the Lake Nyos disaster'', American Physical Society, Division of Fluid Dynamics Meeting, November 21-23, 1999 *Decker, R. and Decker, B. (1997) ''Volcanoes'', 3rd edition, WH Freeman, New York. *Musa, Tansa (28 September 2005). [http://www.alertnet.org/thenews/newsdesk/L28726343.htm "Cameroon dam could collapse in 10 years-UN experts".] Reuters. *Musa, Tansa (18 August 2005). [http://za.today.reuters.com/news/NewsArticle.aspx?type=topNews&storyID=2005-08-18T141819Z_01_ALL851430_RTRIDST_0_OZATP-CAMEROON-CATASTROPHE-20050818.XML"Cameroon dam nears collapse, 10,000 lives at risk".] Reuters. *Sano Y., Kusakabe M., Hirabayashi J. ''et al'' (1990), ''Helium and carbon fluxes in Lake Nyos, Cameroon: constraint on next gas burst'', Earth and Planetary Science Letters, v. 99, p. 303-314 *Sano Y., Wakita H., Ohsumi T., Kusakabe M. (1987), ''Helium isotope evidence for magmatic gases in Lake Nyos, Cameroon'', Geophysical Research Letters, v. 14, p. 1039-1041 *[http://www.eawag.ch/research_e/apec/ Scripts/W%FCest_Schmid_DD_Nyos_FM9_12626.pdf Lake Nyos Research] == External links == * [http://perso.wanadoo.fr/mhalb/nyos/ Lake Nyos incident] * [http://www.biology.lsa.umich.edu/~gwk/research/nyos.html Lake Nyos research] * [http://perso.orange.fr/mhalb/nyos/webcam.htm A webcam on the lake Nyos] * [http://newssearch.bbc.co.uk/onthisday/hi/dates/stories/august/21/newsid_3380000/3380803.stm BBC News 'On This Day' article] * [http://news.bbc.co.uk/1/hi/world/africa/1155057.stm BBC news article about the degassing of Lake Nyos] * [[Horizon (BBC TV series)|BBC Horizon]] episode [http://www.bbc.co.uk/science/horizon/2001/killerlakes.shtml Killer lakes] * [http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyos.html Volcano World information] * [http://vulcan.wr.usgs.gov/Glossary/Lakes/description_volcanic_lakes_gas_release.html USGS information] * [http://www.smithsonianmag.si.edu/smithsonian/issues03/sep03/pdf/killer_lakes.pdf Killer Lakes], [[Smithsonian]] magazine * [http://www.guardian.co.uk/naturaldisasters/story/0,7369,1579123,00.html Gas threat grows from Cameroon's lethal lakes] &mdash; article from ''[[The Guardian]]'' newspaper *[http://news.bbc.co.uk/2/hi/science/nature/4285878.stm BBC News 27 Sep 2005: Action needed on deadly lakes] * [http://www.geology.sdsu.edu/how_volcanoes_work/Nyos.html The eruption at Lake Nyos] from sdsu.edu * [http://svs.gsfc.nasa.gov/search/Series/ExplodingLakes.html NASA Exploding Lakes] * [http://www.nyos.lv/?l=2&m=1&c=&p= Mechanics of the switching on of the trigger mechanism of limnological catastrophes] - [[Latvia]]n research by Nataliya Anatolievna Solodovnik and Anatoliy Borisovich Solodovnik * [http://news.bbc.co.uk/2/hi/africa/6624395.stm BBC Article on Lake Kivu] A similar problem at Lake Kivu and plans to deal with it * [http://www.neatorama.com/2007/05/21/the-strangest-disaster-of-the-20th century/ The Strangest Disaster of the 20th Century] reprinted from Uncle John’s Bathroom Reader: World of Odd. {{DEFAULTSORT:Nyos, Lake}} [[Category:1986]] [[Category:1986 natural disasters]] [[Category:History of Cameroon]] [[Category:Lakes of Cameroon]] [[Category:Maar volcanoes]] [[Category:Mbéré Rift Valley]] [[Category:Meromictic lakes]] [[Category:Rift volcanoes]] [[Category:Volcanoes of Cameroon]] [[Category:Volcanic events]] [[Category:Gas explosions]] [[Category:Crater lakes]] [[Category:Explosions in Cameroon]] [[af:Nyosmeer]] [[ca:Llac Nyos]] [[de:Nyos-See]] [[es:Lago Nyos]] [[eo:Nyos]] [[fr:Lac Nyos]] [[id:Danau Nyos]] [[it:Lago Nyos]] [[he:אגם ניוס]] [[lv:Niosas ezers]] [[lt:Nioso ežeras]] [[hu:Nyos-tó]] [[ms:Tasik Nyos]] [[ja:ニオス湖]] [[pl:Nyos]] [[pt:Lago Nyos]] [[ro:Nyos]] [[ru:Ниос]] [[sk:Nyos (jazero)]] [[fi:Nyosjärvi]]