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{{Infobox body of water|name=Danau Nyos|image=Nyos Lake.jpg|caption=|image_bathymetry=|caption_bathymetry=|location=[[Region Barat Laut, Kamerun]]|coords={{coord|06|26|17|N|010|17|56|E|type:waterbody_region:CM|display=inline,title}}|type=[[Danau meromiktik|Meromiktik]], [[Letusan limnik|danau limnik aktif]], [[danau kawah]]|inflow=''sumber subakuatik''|outflow=|catchment=|basin_countries=Kamerun|length={{convert|2,0|km|mi|abbr=on}}|width={{convert|1,2|km|mi|abbr=on}}|area={{convert|1,58|km2|acre|abbr=on}}|depth={{convert|94,9|m|ft|abbr=on}}|max-depth={{convert|208|m|ft|abbr=on}}|volume={{convert|0,15|km3|}}|residence_time=|shore=|elevation={{convert|1091|m|ft|abbr=on}}|islands=|cities=<!-- Map -->|pushpin_map=Cameroon#Africa|pushpin_label_position=|pushpin_map_alt=Lokasi Danau Nyos di Kamerun.|pushpin_map_caption=<!-- Below -->|website=|reference=}}
[[Image:Lake_nyos.jpg|right|350px|thumb|Lake Nyos, Cameroon]]
'''Danau Nyos''' adalah sebuah danau [[kawah gunung api]] di [[Kamerun]], [[Afrika Barat]], terletak di {{coor d|6.36|N|10.15|E}}. Pada [[1986]] danau ini melepaskan awan raksasa [[karbon dioksida]], yang mengakibatkan [[sufokasi]] (kekurangan oksigen) sampai 1800 orang di desa sekitarnya.▼
 
▲'''Danau Nyos''' adalah sebuah danau [[kawah gunung api]] di [[Kamerun]], [[Afrika Barat]], terletak di {{coor d|6.36|N|10.15|E}}. Pada [[1986]] danau ini melepaskan awan raksasa [[karbon dioksida]], yang mengakibatkan [[sufokasi]] (kekurangan [[oksigen]]) sampai 1800 orang di desa sekitarnya.
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==Formation and geological history==
 
Kantong magma yang terletak di dasar danau ini mengeluarkan [[karbon dioksida]] ke dalam air, mengubahnya menjadi [[asam karbonat]]. Nyos adalah salah satu dari tiga danau yang diketahui jenuh dengan karbon dioksida akibat mekanisme ini, dan karenanya rentan terhadap [[letusan limnik]].
[[Image:Lake_nyos_map.jpg|left|thumb|150px|Map showing the location of Lake Nyos]]
Lake Nyos fills a roughly circular [[maar]] in the [[Oku Volcanic Field]], an explosion crater caused when a [[lava flow]] interacts violently with [[groundwater]]. The maar is believed to have formed in an eruption about 400 years ago, and is 1,800 m (5,900 feet) across and 208 m (682 feet) deep. 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 crustal 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.
 
==Gas saturationLihat pula ==
 
* [[Hukum Henry]]▼
Lake Nyos is one of only three lakes in the world known to be saturated with [[carbon dioxide]] - the others are [[Lake Monoun]], also in Cameroon about 100km 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 [[kilogram]]s of CO<sub>2</sub> annually.
* [[Hukum Raoult]].▼
 
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 the cold water at the lake's bottom is dissolved in great amounts.
 
For most of the time, the lake waters are 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:Cow killed by Lake Nyos gasses.jpg|thumb|right|150px|A cow suffocated by gasses 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. On [[August 21]], [[1986]], an event occurred at Lake Nyos which triggered the sudden release of about 1.6 million [[tonne]]s of CO<sub>2</sub>. The gas rushed up two nearby valleys, displacing all the air and suffocating up to 1800 people within 20&nbsp;km of the lake.
 
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 caused 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 CO<sub>2</sub> is denser than [[air]], the gas flowed up two valleys in a layer tens of metres deep, displacing the air and suffocating all the people and animals. 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 ==
 
The scale of the disaster led to much study on how a similar occurrence could be prevented. Estimates of the rate of carbon dioxide entering the lake suggested that outgassings could occur every 10-30 years.
 
The solution proposed by scientists to the threat posed by Lake Nyos was that pipes should be extended into the lower regions of the lake, allowing a controlled and continuous outgassing. International efforts have since installed a pipe running from the surface anchored to a [[raft]] that allows the deeper areas of the lake to release their CO<small><sub>2</sub></small> to the surface in controlled small amounts. It is hoped this will reduce the maximum levels of CO<small><sub>2</sub></small> in the future, and prevent any possibility of the lake turning over. Degassing began in 2001 and is continuing steadily.
 
Following the Lake Nyos tragedy, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. [[Lake Kivu]] in [[Rwanda]], 2000 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.
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== Lihat juga ==
 
▲*[[Hukum Henry]]
▲*[[Hukum Raoult]].
 
== Referensi ==
 
* 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.
* 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. &nbsp;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. &nbsp;1039-1041
 
== Pranala luar ==
 
* [http://perso.wanadoo.fr/mhalb/nyos/ Lake Nyos incident] {{Webarchive|url=https://web.archive.org/web/20060424195401/http://perso.wanadoo.fr/mhalb/nyos/ |date=2006-04-24 }}
* [http://www.biology.lsa.umich.edu/~gwk/research/nyos.html Lake Nyos research] {{Webarchive|url=https://web.archive.org/web/20060210053007/http://www.biology.lsa.umich.edu/%7Egwk/research/nyos.html |date=2006-02-10 }}
* [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 (television)|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] {{Webarchive|url=https://web.archive.org/web/20080509122156/http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyos.html |date=2008-05-09 }}
* [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
 
[[Kategori:Danau di Afrika|Nyos]]
 
[[af:Nyosmeer]]
[[de:Nyos-See]]
[[en:Lake Nyos]]
[[eo:Nyos]]
[[fi:Nyosjärvi]]
[[fr:Lac Nyos]]
[[he:אגם ניוס]]
[[hu:Nyos-tó]]
[[it:Lago Nyos]]
[[ja:ニオス湖]]
[[lt:Nioso ežeras]]
[[lv:Niosas ezers]]
[[pl:Nyos]]
[[pt:Lago Nyos]]
[[ro:Nyos]]
[[ru:Ниос]]
[[sk:Nyos (jazero)]]
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