Lake Nyos

"Nyos" redirects here. For the orchestra, seeNational Youth Orchestra of Scotland.

Lake Nyos
Lake Nyos Lake Nyos
Location	Northwest Region, Cameroon
Coordinates	06°26′17″N010°17′56″E
Type	Meromictic,limnically active lake,volcanic crater lake
Primary inflows	subaquatic source
Basincountries	Cameroon
Max. length	2.0 km (1.2 mi)
Max. width	1.2 km (0.75 mi)
Surface area	1.58 km2(390 acres)
Average depth	94.9 m (311 ft)
Max. depth	208 m (682 ft)
Water volume	0.15 km3(120,000 acre⋅ft)
Surface elevation	1,091 m (3,579 ft)

Lake Nyos(/ˈniːoʊs/NEE-ohs)is acrater lakein theNorthwest RegionofCameroon,located about 315 km (196 mi) northwest ofYaoundé,the capital.Nyos is a deeplakehigh on the flank of an inactivevolcanoin theOku volcanic plainalong theCameroon lineof volcanic activity. Avolcanic damimpounds the lake waters.

A pocket ofmagmalies beneath the lake and leakscarbon dioxide(CO₂) into the water, changing it intocarbonic acid.Nyos is one of only three lakes known to be saturated with carbon dioxide in this way, and therefore prone tolimnic eruptions(the others beingLake Monoun,also in Cameroon, andLake Kivuin theDemocratic Republic of CongoandRwanda).

In 1986, possibly as the result of a landslide,Lake Nyos suddenly emitted a large cloud of CO₂,whichsuffocated1,746 peopleand 3,500 livestock in nearby towns and villages, the most notable one beingChah,which was abandoned after the incident.The limnic eruption not only devastated human and livestock populations but also had a profound impact on the diverse aquatic life, including tilapia, crabs, snails, and frogs, leading to a significant loss of biodiversity in and around the lake.

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. A geological tremor could cause this naturalleveeto give way, allowing water to rush into downstream villages all the way intoNigeriaand allowing large amounts of carbon dioxide to escape.

Geography

Lake and vicinity fromLandsat 8,2014

Lake Nyos lies within theOku Volcanic Field,located near the northern boundary of the Cameroon Volcanic Line, a zone of volcanoes and other tectonic activity that extends southwest to the Mt. Cameroonstratovolcano.The field consists of volcanicmaarsand basalticscoria cones.

Formation and geologic history

Lake Nyos is located south of the dirt road fromWum,about 30 km (19 mi) to the west, toNkambéin the east. Villages along the road in the vicinity of the lake includeCha,Nyos, Munji, Djingbe, and Subum. The lake is 50 km (31 mi) from the Nigerian border to the north, and lies on the northern slopes of theMassif du Mbam,drained by streams running north, then northwest, to the Katsina-Ala River in Nigeria which is part of theBenue Riverbasin.

Lake Nyos fills a roughly circularmaarin theOku Volcanic Field,an explosion crater caused when alava flowinteracted violently withgroundwater.The maar is believed to have formed in an eruption a maximum of 12,000 years ago, and is 1,800 m (5,900 ft) across and 208 m (682 ft) deep.The area has been volcanically active for millions of years—afterSouth AmericaandAfricawere split apart byplate tectonicsabout 110 million years ago,West Africaalso experienced rifting, although to a lesser degree. The rift is known as theMbéré Rift Valley,andcrustalextension has allowedmagmato reach the surface along a line extending through Cameroon.Mount Cameroonalso lies on this fault line. Lake Nyos is surrounded by old lava flows andpyroclasticdeposits.

Although Nyos is situated within an extinct volcano, magma still exists beneath it. Approximately 80 kilometres (50 mi) directly below the lake resides a pool ofmagma,which releases carbon dioxide and other gases; the gases then travel upward through the earth. The fumes then dissolve in the natural springs encircling the lake, ultimately rising to the surface of the water and leaching into the lake. But with advanced in technology now there are machinery placed at the bottom of the lake to remove the gases, so as to make the inhabitants of the area free from danger.

The lake waters are held in place by a naturaldamcomposed ofvolcanic rock.At its narrowest point, the wall measures 40 metres (130 ft) high and 45 metres (148 ft) wide.

Gas saturation

Lake Nyos is one of only three lakes in the world known to be saturated with carbon dioxide—the others areLake Monoun,also in Cameroon, andLake Kivuon the border between theDemocratic Republic of the CongoandRwanda.Amagma chamberbeneath 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 milliontonnesof CO₂.

Lake Nyos is thermallystratified,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 CO₂remains in solution in the lower layers. However, over time, the water becomessupersaturated,and if an event such as anearthquakeorlandslideoccurs, large amounts of CO₂may suddenly come out of solution.

1986 disaster

Main article:Lake Nyos disaster

Lake Nyos as it appeared just over a week after the eruption; August 29, 1986.

Although a suddenoutgassingof CO₂had occurred atLake Monounin 1984, a similar threat from Lake Nyos was not anticipated. However, on August 21, 1986, alimnic eruptionoccurred at Lake Nyos, triggering the sudden release of about 100,000–300,000tons(some sources state as much as 1.6 million tonnes)of CO₂.This gas cloud rose at nearly 100 kilometres per hour (62 mph) andspilled 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.

Cattlesuffocated by carbon dioxide from Lake Nyos

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 mi xing of the supersaturated deep water with the upper layers of the lake, where the reduced pressure allowed the stored CO₂toeffervesceout 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 toiron-rich water from the deep rising to the surface and beingoxidisedby the air. The level of the lake dropped by about a metre and trees near the lake were knocked down.

Degassing

See also:Limnic eruption § Degassing

The scale of the 1986 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 showsthat 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. These use a pump to initially lift water from the bottom of the lake, heavily saturated with CO₂,until the loss of pressure begins releasing the gas from the diphasic fluid, at which point the process becomes self-powered.In 1992 at Monoun, and in 1995 at Nyos, a French team directed by Michel Halbwachs demonstrated the feasibility of this approach. In 2001, the U.S.Office of Foreign Disaster Assistancefunded a permanent installation at Nyos.

In 2011, two additional pipes were installed by Michel Halbwachs and his French-Cameroonian team to assure the complete degassing of Lake Nyos.

Degassing pump schematic

Following the disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere.Lake Kivu,2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence for outgassing events around the lake about every thousand years. The eruption of nearbyMount Nyiragongoin 2002 sentlavaflowing into the lake, raising fears that a gas eruption could be triggered, but it was not, as the flow of lava stopped well before it got near the bottom layers of the lake, where the gas is maintained in solution by the water pressure.

Weakening dam

In 2005, Isaac Njilah, a geologist at theUniversity of Yaoundé,suggested that the natural dam ofvolcanic rockthat keeps in the lake's waters could collapse in the near future.Erosionhas 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 m³(1.8 billion ft³) of water flooding downhill into areas of the Northwest Province and the Nigerian states ofTarabaandBenue.

The Cameroonian government, speaking through Gregory Tanyi-Leke of the Institute of Mining and Geological Research, acknowledges the weakening wall, but denies that it presents any immediate threat. AUnited Nationsteam led by Olaf Van Duin and Nisa Nurmohamed of theNetherlands' 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 believed that the dam would breach within the next 10 to 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 m (66 ft), the pressure on the wall would be reduced significantly.

Return of population

Despite the risks from carbon dioxide and collapse of the lake's retaining wall, the area is being resettled. Settlers cite the wish to return to ancestral lands (although some are newcomers) and the great fertility of the land as reasons for their return.

In popular culture

Nyos: Η τελετή της αθωότητας[Nyos: The ceremony of innocence] (2016), a novel by Basileios Drolias focusing on the lake Nyos disaster.

Stikvallei[Choke Valley] (2013), a non-fiction account of the lake Nyos disaster byFrank Westerman.

See also

• Carbon sequestration– Storing carbon in a carbon pool
• Limnic eruption– Type of natural disaster
• Limnology– Science of inland aquatic ecosystems
• Mazuku– Pocket of carbon dioxide–rich air that can be lethal
• Meromictic lake– Permanently stratified lake with layers of water that do not intermix

Further reading

• "Cameroon scientist denies dam about to collapse"(August 23, 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 (September 28, 2005)."Cameroon dam could collapse in 10 years-UN experts".Reuters.
• Musa, Tansa (August 18, 2005)."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
• Stager, J.C. (1987), "Silent Death from Cameroon's Killer Lake", National Geographic, September 1987
• Gideon Aghaindum, Ajeagah (2017) "Eco-autopsy of the lake Nyos disaster in Cameroon: 30 Years After Calamity".

External links

• Media related toLake Nyosat Wikimedia Commons
• Lake Nyos Degassing: in 1995 Michel HALBWACHS with his french scientist team found the solution for lake Nyos degassing problemArchivedNovember 30, 2021, at theWayback Machine
• Lake Nyos incident
• BBC News 'On This Day' article
• BBC news article about the degassing of Lake Nyos
• BBC HorizonepisodeKiller lakes
• USGS information
• Defusing Africa’s Killer Lakes–Smithsonian
• Gas threat grows from Cameroon's lethal lakes—The Guardian
• Lake Nyos – The Vanguard, CameroonArchivedSeptember 4, 2015, at theWayback Machine
• BBC News 27 Sep 2005: Action needed on deadly lakes
• Mechanics of the switching on of the trigger mechanism of limnological catastrophes–Latvianresearch by Nataliya Anatolievna Solodovnik and Anatoliy Borisovich Solodovnik
• BBC Article on Lake KivuA similar problem at Lake Kivu and plans to deal with it
• The Strangest Disaster of the 20th Centuryreprinted from Uncle John's Bathroom Reader: World of Odd.