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43-562: Lake Nyos ( / ˈ n iː oʊ s / NEE -ohs ) is a crater lake in the Northwest Region of Cameroon , located about 315 km (196 mi) northwest of Yaoundé , the capital. 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 volcanic dam impounds the lake waters. A pocket of magma lies beneath

86-418: A limnic eruption occurred at Lake Nyos, triggering the sudden release of about 100,000–300,000 tons (some sources state as much as 1.6 million tonnes) of CO 2 . This gas cloud rose at nearly 100 kilometres per hour (62 mph) and spilled 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

129-454: A pyroclastic density current or a pyroclastic cloud ) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra ) that flows along the ground away from a volcano at average speeds of 100 km/h (30 m/s; 60 mph) but is capable of reaching speeds up to 700 km/h (190 m/s; 430 mph). The gases and tephra can reach temperatures of about 1,000 °C (1,800 °F). Pyroclastic flows are

172-425: A large cloud of CO 2 , which suffocated 1,746 people and 3,500 livestock in nearby towns and villages, the most notable one being Chah , 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

215-448: 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. 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

258-425: A pyroclastic flow traveled for several hundreds of meters above the sea. A pyroclastic flow can interact with a body of water to form a large amount of mud, which can then continue to flow downhill as a lahar . This is one of several mechanisms that can create a lahar. In 1963, NASA astronomer Winifred Cameron proposed that the lunar equivalent of terrestrial pyroclastic flows may have formed sinuous rilles on

301-438: A research team at Kiel University , Germany, of pyroclastic flows moving over the water. When the reconstructed pyroclastic flow (stream of mostly hot ash with varying densities) hit the water, two things happened: the heavier material fell into the water, precipitating out from the pyroclastic flow and into the liquid; the temperature of the ash caused the water to evaporate, propelling the pyroclastic flow (now only consisting of

344-425: 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 mixing of the supersaturated deep water with the upper layers of the lake, where the reduced pressure allowed the stored CO 2 to effervesce out of solution. It is believed that about 1.2 cubic kilometres (0.29 cu mi) of gas

387-400: 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

430-467: Is 1,800 m (5,900 ft) across and 208 m (682 ft) 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

473-619: Is located in the caldera of Mount Mazama . It is the deepest lake in the United States with a depth of 594 m (1,949 ft). Crater Lake is fed solely by falling rain and snow, with no inflow or outflow at the surface, and hence is one of the clearest lakes in the world. The highest volcano in the world, 6,893-m (22,615-ft) Ojos del Salado in Chile , has a permanent crater lake about 100 m (330 ft) in diameter at an elevation of 6,390 m (20,965 ft) on its eastern side. This

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516-440: Is most likely the highest lake of any kind in the world. Due to their unstable environments, some crater lakes exist only intermittently. Caldera lakes in contrast can be quite large and long-lasting. For instance, Lake Toba ( Indonesia ) formed after its eruption around 75,000 years ago. At around 100 kilometres (62 mi) by 30 kilometres (19 mi) in extent and 505 metres (1,657 ft) deep at its deepest point, Lake Toba

559-548: Is sometimes abbreviated to PDC (pyroclastic density current). Several mechanisms can produce a pyroclastic flow: Flow volumes range from a few hundred cubic meters to more than 1,000 cubic kilometres (240 cu mi). Larger flows can travel for hundreds of kilometres, although none on that scale has occurred for several hundred thousand years. Most pyroclastic flows are around one to ten cubic kilometres ( 1 ⁄ 4 – 2 + 1 ⁄ 2  cu mi) and travel for several kilometres. Flows usually consist of two parts:

602-508: Is the largest crater lake in the world. While many crater lakes are picturesque, they can also be deadly. Gas discharges from Lake Nyos in Cameroon suffocated 1,800 people in 1986, and crater lakes such as Mount Ruapehu 's (New Zealand) often contribute to destructive lahars . Certain bodies of water, although their formation is directly related to volcanic activity, are not usually referred to as crater lakes, including: Pyroclastic flow A pyroclastic flow (also known as

645-525: Is weakening. A geological tremor could cause this natural levee to give way, allowing water to rush into downstream villages all the way into Nigeria and allowing large amounts of carbon dioxide to escape. Lake Nyos lies within the Oku Volcanic Field , located near the northern boundary of the Cameroon Volcanic Line, a zone of volcanoes and other tectonic activity that extends southwest to

688-524: The 1883 eruption of Krakatoa , supported by experimental evidence, shows that pyroclastic flows can cross significant bodies of water. However, that might be a pyroclastic surge , not flow, because the density of a gravity current means it cannot move across the surface of water. One flow reached the Sumatran coast as far as 48 kilometres (26 nautical miles) away. A 2006 BBC documentary film, Ten Things You Didn't Know About Volcanoes , demonstrated tests by

731-639: The basal flow hugs the ground and contains larger, coarse boulders and rock fragments, while an extremely hot ash plume lofts above it because of the turbulence between the flow and the overlying air, admixing and heating cold atmospheric air causing expansion and convection. Flows can deposit less than 1 meter to 200 meters in depth of loose rock fragment. The kinetic energy of the moving cloud will flatten trees and buildings in its path. The hot gases and high speed make them particularly lethal, as they will incinerate living organisms instantaneously or turn them into carbonized fossils: Testimonial evidence from

774-418: The crater rim , is filled by water. The water may come from precipitation , groundwater circulation (often hydrothermal fluids in the case of volcanic craters) or melted ice . Its level rises until an equilibrium is reached between the rates of incoming and outgoing water. Sources of water loss singly or together may include evaporation , subsurface seepage, and, in places, surface leakage or overflow when

817-510: The Mt. Cameroon stratovolcano . The field consists of volcanic maars and basaltic scoria cones . Lake Nyos is located south of the dirt road from Wum , about 30 km (19 mi) to the west, to Nkambé 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 (31 mi) from the Nigerian border to the north, and lies on

860-574: The Northwest Province and the Nigerian states of Taraba and Benue . 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. A United Nations team led by Olaf Van Duin and Nisa Nurmohamed of the Netherlands ' Ministry of Transport and Public Works inspected

903-412: 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. 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

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946-491: 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),

989-674: The dark is nuée ardente (French, "burning cloud"); this was notably used to describe the disastrous 1902 eruption of Mount Pelée on Martinique , a French island in the Caribbean. Pyroclastic flows that contain a much higher proportion of gas to rock are known as "fully dilute pyroclastic density currents" or pyroclastic surges . The lower density sometimes allows them to flow over higher topographic features or water such as ridges, hills, rivers, and seas. They may also contain steam, water, and rock at less than 250 °C (480 °F); these are called "cold" compared with other flows, although

1032-431: 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 natural dam composed of volcanic rock . At its narrowest point,

1075-406: The lake Nyos disaster. Stikvallei [Choke Valley] (2013), a non-fiction account of the lake Nyos disaster by Frank Westerman . Volcanic crater lake Lakes in calderas fill large craters formed by the collapse of a volcano during an eruption. Lakes in maars fill medium-sized craters where an eruption deposited debris around a vent. Crater lakes form as the created depression, within

1118-473: 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 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. In 2005, Isaac Njilah, a geologist at the University of Yaoundé , suggested that

1161-534: The lake and leaks carbon dioxide (CO 2 ) into the water, changing it into carbonic acid . Nyos is one of only three lakes known to be saturated with carbon dioxide in this way, and therefore prone to limnic eruptions (the others being Lake Monoun , also in Cameroon, and Lake Kivu in the Democratic Republic of Congo and Rwanda ). In 1986, possibly as the result of a landslide, Lake Nyos suddenly emitted

1204-401: The lake bed, charging the waters of Lake Nyos with an estimated 90 million tonnes of CO 2 . 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,

1247-464: The lake is stable and the CO 2 remains in solution in the lower layers. However, over time, the water becomes supersaturated , and if an event such as an earthquake or landslide occurs, large amounts of CO 2 may suddenly come out of solution. Although a sudden outgassing of CO 2 had occurred at Lake Monoun in 1984, a similar threat from Lake Nyos was not anticipated. However, on August 21, 1986,

1290-438: The lake level reaches the lowest point on its rim. At such a saddle location, the upper portion of the lake is contained only by its adjacent natural volcanic dam ; continued leakage through or surface outflow across the dam can erode its included material, thus lowering lake level until a new equilibrium of water flow, erosion, and rock resistance is established. If the volcanic dam portion erodes rapidly or fails catastrophically,

1333-402: 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

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1376-406: 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

1419-432: The lake. These use a pump to initially lift water from the bottom of the lake, heavily saturated with CO 2 , 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 Assistance funded

1462-485: The lighter material) along on a bed of steam at an even faster pace than before. During some phases of the Soufriere Hills volcano on Montserrat, pyroclastic flows were filmed about 1 km ( 1 ⁄ 2  nmi) offshore. These show the water boiling as the flow passes over it. The flows eventually built a delta, which covered about 1 km (250 acres). Another example was observed in 2019 at Stromboli when

1505-539: The most deadly of all volcanic hazards and are produced as a result of certain explosive eruptions ; they normally touch the ground and hurtle downhill or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. The word pyroclast is derived from the Greek πῦρ ( pýr ), meaning "fire", and κλαστός ( klastós ), meaning "broken in pieces". A name for pyroclastic flows that glow red in

1548-515: 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 m (1.8 billion ft) of water flooding downhill into areas of

1591-634: The northern slopes of the Massif du Mbam , drained by streams running north, then northwest, to the Katsina-Ala River in Nigeria which is part of the Benue River basin. 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 a maximum of 12,000 years ago, and

1634-447: The occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of such floods is common to all natural dam types. These lakes may become soda lakes , many of which are associated with active tectonic and volcanic zones. A well-known crater lake, which bears the same name as the geological feature, is Crater Lake in Oregon . It

1677-434: The pressure on the wall would be reduced significantly. 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. Nyos: Η τελετή της αθωότητας [Nyos: The ceremony of innocence] (2016), a novel by Basileios Drolias focusing on

1720-431: 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 deposits. 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 of magma , which releases carbon dioxide and other gases; the gases then travel upward through

1763-436: The temperature is still lethally high. Cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. Fronts of some pyroclastic density currents are fully dilute; for example, during the eruption of Mount Pelée in 1902, a fully dilute current overwhelmed the city of Saint-Pierre and killed nearly 30,000 people. A pyroclastic flow is a type of gravity current ; in scientific literature, it

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1806-462: The wall measures 40 metres (130 ft) high and 45 metres (148 ft) wide. 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, and Lake Kivu on the border between the Democratic Republic of the Congo and Rwanda . A magma chamber beneath the region is an abundant source of carbon dioxide, which seeps up through

1849-414: Was released. 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. 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

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