terravelCameroon · Africa
Lake Nyos
What is Lake Nyos, and where is it?
Lake Nyos is a crater lake in northwestern Cameroon, located 315 kilometers from the capital Yaoundé. Perched on an inactive volcano's flank within the Oku volcanic plain, it sits along the Cameroon volcanic line. The lake is notable for being saturated with carbon dioxide from magma beneath it, making it one of only three such lakes globally.
Location on the Cameroon Volcanic Line
Lake Nyos occupies a crater in the Oku Volcanic Field, near the northern boundary of the Cameroon Volcanic Line—a zone of volcanic and tectonic activity extending southwest toward Mount Cameroon. The lake sits approximately 315 kilometers northwest of Yaoundé and lies 50 kilometers south of the Nigerian border. Nearby villages include Cha, Nyos, Munji, Djingbe, and Subum, accessible via a dirt road connecting Wum to the west and Nkambé to the east. Streams draining the northern slopes of the Massif du Mbam flow north and northwest from the lake toward the Katsina-Ala River in Nigeria, which feeds into the Benue River basin.
The Cameroon Volcanic Line itself reflects deep geological history. After South America and Africa separated through plate tectonics roughly 110 million years ago, West Africa experienced rifting, though less intensely. This rifting, known as the Mbéré Rift Valley, allowed magma to reach the surface along a line extending through Cameroon. The crustal extension continues to shape the region's volcanic character, with Mount Cameroon also positioned on this fault line. Lake Nyos thus represents one node in a broader pattern of volcanism that has defined the landscape for millions of years.
Formation as an Explosion Crater
Lake Nyos fills a roughly circular maar—an explosion crater formed when lava interacted violently with groundwater. Geologists believe the crater formed within the past 12,000 years. The lake measures approximately 1,800 meters across and reaches a depth of 208 meters. A natural dam of volcanic rock holds the water in place; at its narrowest point, this barrier stands 40 meters high and 45 meters wide. The surrounding landscape bears the geological signature of its origins: old lava flows and pyroclastic deposits encircle the lake, remnants of the violent forces that carved the crater.
Beneath the lake, approximately 80 kilometers directly below the surface, a pool of magma continues to release carbon dioxide and other gases. These fumes travel upward through the earth, dissolving in natural springs that encircle the lake before rising to the surface and leaching into the water. This ongoing subsurface activity distinguishes Lake Nyos from typical crater lakes. The lake's waters are thermally stratified, with colder, denser, CO2-saturated water accumulating in the lower layers while warmer water remains above. Over long periods, carbon dioxide gas is absorbed in great quantities, creating conditions that make the lake geologically unique and potentially hazardous.
Carbon Dioxide Saturation and the 1986 Disaster
Lake Nyos is one of only three lakes in the world known to be saturated with carbon dioxide, alongside Lake Monoun in Cameroon and Lake Kivu, which straddles the Democratic Republic of Congo and Rwanda. The saturation results from magma beneath the region continuously seeping carbon dioxide into the lake. Usually the lake remains stable, with CO2 confined to lower layers. Over time, however, the water becomes supersaturated. If a disturbance occurs—such as an earthquake, landslide, or heavy rainfall triggering overturn—large amounts of CO2 can suddenly escape.
On August 21, 1986, such an event occurred. A limnic eruption released an estimated 100,000 to 300,000 tons of CO2 (some sources cite as much as 1.6 million tonnes). The gas cloud rose at nearly 100 kilometers per hour and spilled over the northern lip of the lake into a valley running east to west from Cha to Subum, then rushed down two valleys branching northward. The cloud displaced all air in its path, suffocating 1,746 people within 25 kilometers of the lake and killing 3,500 livestock. Villages most affected were Cha, Nyos, and Subum; Cha was abandoned after the incident. The normally blue lake waters turned deep red as iron-rich water from the depths rose and oxidized in air. The lake level dropped approximately one meter. Scientists believe a landslide most likely triggered the catastrophe, though a small volcanic eruption on the lake bed or cool rainwater causing overturn remain possible explanations.
Degassing Systems and Ongoing Risks
The 1986 disaster prompted urgent research into prevention methods. Estimates suggested outgassings could occur every 10 to 30 years. In response, researchers proposed degassing columns that use pumps to lift water from the lake's bottom, where CO2 saturation is highest. As pressure decreases during ascent, gas is released safely into the atmosphere. A French team directed by Michel Halbwachs demonstrated feasibility at Lake Monoun in 1992 and at Lake Nyos in 1995. The U.S. Office of Foreign Disaster Assistance funded a permanent installation at Nyos in 2001, with two additional pipes installed in 2011 by Halbwachs and his French-Cameroonian team.
Beyond gas saturation, the lake faces a second threat: the natural volcanic dam weakens. Erosion has created holes and pockets in the upper layer, and water already seeps through the lower section. Landslides have reduced external dam strength. A geological tremor could cause the wall to fail, potentially releasing up to 50 million cubic meters of water into downstream areas of Cameroon's Northwest Province and Nigerian states of Taraba and Benue. In 2005, a United Nations team confirmed the dam had weakened, with one expert predicting breach within 10 to 20 years—a scenario that has not yet occurred. The Cameroonian government denies any immediate threat. Possible mitigation includes strengthening the wall or introducing a drainage channel to lower the water level by approximately 20 meters, which would reduce pressure significantly.
Resettlement and Ecological Recovery
Despite the documented risks from carbon dioxide saturation and dam failure, the area surrounding Lake Nyos is being resettled. Inhabitants cite ancestral ties to the land and the exceptional fertility of the soil as reasons for returning. Some settlers are newcomers attracted by agricultural potential. This resettlement occurs alongside ongoing degassing efforts and monitoring, reflecting a complex negotiation between geological hazard and human attachment to place.
The 1986 disaster caused profound ecological damage. The sudden release of CO2 and the subsequent chemical changes in the lake devastated aquatic life, including tilapia, crabs, snails, and frogs, resulting in significant biodiversity loss. The lake's ecosystem has been recovering since, though the long-term effects of continued degassing operations on aquatic communities remain an area of scientific interest. The disaster also prompted investigation of other African lakes; Lake Kivu, 2,000 times larger than Lake Nyos, was found to be similarly supersaturated, with geological evidence suggesting outgassing events occur approximately every thousand years.
Lake Nyos at a glance
Questions about Lake Nyos
What caused the 1986 Lake Nyos disaster?
On August 21, 1986, a limnic eruption released 100,000 to 300,000 tons of carbon dioxide from the lake. The trigger remains uncertain; most geologists suspect a landslide, though a small volcanic eruption, cool rainwater causing overturn, or an earthquake are also possible. The event killed 1,746 people and 3,500 livestock within 25 kilometers of the lake.
How do the degassing tubes work?
Degassing columns use pumps to lift water from the lake's bottom, where CO2 saturation is highest. As pressure decreases during ascent, carbon dioxide is released safely into the atmosphere. Once initiated, the process becomes self-powered. A permanent installation was funded in 2001, with two additional pipes added in 2011.
Why is Lake Nyos saturated with carbon dioxide?
A pool of magma lies approximately 80 kilometers directly beneath the lake. This magma continuously releases carbon dioxide and other gases that travel upward through the earth, dissolving in natural springs around the lake before leaching into the water. Over long periods, the lake absorbs CO2 in great quantities, becoming supersaturated.
What other lakes have similar carbon dioxide saturation?
Only two other lakes are known to be saturated with carbon dioxide: Lake Monoun, also in Cameroon, and Lake Kivu, which is shared by the Democratic Republic of Congo and Rwanda. Lake Kivu is 2,000 times larger than Lake Nyos and shows geological evidence of outgassing events occurring approximately every thousand years.
Is the natural dam at Lake Nyos at risk of collapse?
Yes. Erosion has weakened the volcanic rock dam, creating holes and pockets in the upper layer, with water already seeping through lower sections. Landslides have reduced external strength. A geological tremor could cause failure, potentially releasing up to 50 million cubic meters of water downstream. A 2005 UN team confirmed weakening, though predictions of imminent collapse have not materialized.
Sources and further reading
This article was written from the reference material below, retrieved and reviewed for source alignment on September 13, 2026. Use official local sources for changing access or travel information.
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Test yourself
Which African lake is held back by a volcanic dam and sits atop an inactive volcano in a remote caldera?
Lake Nyos in Cameroon is uniquely defined by its location on an inactive volcano's flank, held back by a natural volcanic dam that creates the crater lake—a geological feature not shared by High Atlas (a mountain range), Nyungwe Forest (a rainforest), or Osun-Osogbo Grove (a sacred grove).
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