Lake Nyos Disaster
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On 21 August 1986, a limnic eruption at Lake Nyos in northwestern
Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...
killed 1,746 people and 3,500 livestock. The eruption triggered the sudden release of about 100,000–300,000 tons of
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
(CO2). The gas cloud initially rose at nearly and then, being heavier than air, descended onto nearby villages, suffocating people and livestock within of the lake. A degassing system has since been installed at the lake, with the aim of reducing the concentration of in the waters and therefore the risk of further eruptions. Along with the Lake Monoun disaster two years earlier, it is one of only two recorded limnic eruptions in history.


Eruption and gas release

What triggered the catastrophic
outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (whic ...
is not known. Most geologists suspect a
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
, but some believe that a small
volcanic eruption A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...
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 because witnesses did not report feeling any tremors on the morning of the disaster, this hypothesis is unlikely. The event resulted in the
supersaturated In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. Most commonly the term is applied to a solution of a solid in a ...
deep water rapidly mixing with the upper layers of the lake, where the reduced pressure allowed the stored to effervesce out of solution. It is believed that about of gas was released. The normally blue waters of the lake turned a deep red after the outgassing, due to
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
-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. Scientists concluded from evidence that a column of water and foam formed at the surface of the lake, spawning a wave of at least that swept the shore on one side. Since carbon dioxide is 1.5 times the density of air, the cloud hugged the ground and moved down the valleys, where there were various villages. The mass was about thick, and travelled downward at . For roughly , the gas cloud was concentrated enough to suffocate many people in their sleep in the villages of Nyos, Kam, Cha, and Subum. About 4,000 inhabitants fled the area, and many of these developed respiratory problems,
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...
s, and
paralysis Paralysis (: paralyses; also known as plegia) is a loss of Motor skill, motor function in one or more Skeletal muscle, muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory d ...
as a result of the gas cloud. It is a possibility that other
volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (Vesicular texture, vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from ...
es were released along with the , as some survivors reported a smell of gunpowder or rotten eggs, which indicates that
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
and
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
were present at concentrations above their odour thresholds. However, was the only gas detected in samples of lake water, suggesting that this was the predominant gas released and as such the main cause of the incident.


Effects on survivors

Reporters in the area described the scene as "looking like the aftermath of a neutron bomb." One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:Following the eruption, many survivors were treated at the main hospital in
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, the country's capital. It was believed that many of the victims had been poisoned by sulphur-based gases. Poisoning by these gases would lead to burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled. Interviews with survivors and pathologic studies indicated that victims rapidly lost consciousness and that death was caused by asphyxiation. At nonlethal levels, can produce sensory hallucinations, such that many people exposed to report the odor of sulfuric compounds when none are present. Skin lesions found on survivors represent pressure sores, and in a few cases exposure to a heat source, but there is no evidence of chemical burns or of flash burns from exposure to hot gases.


Degassing

The scale of the disaster led to much study on how a recurrence could be prevented. Several researchers proposed the installation of degassing columns from rafts in the middle of the lake. The principle is to slowly vent the by lifting heavily saturated water from the bottom of the lake through a pipe, initially by using a pump, but only until the release of gas inside the pipe naturally lifts the column of effervescing water, making the process self-sustaining. : Starting from 1995, feasibility studies were successfully conducted, and the first permanent degassing pipe was installed at the lake in 2001. Two additional pipes were installed in 2011. In 2019 it was determined that the degassing had reached an essentially steady state and that a single one of the installed pipes would be able to self-sustain the degassing process into the future, indefinitely maintaining the at a safe level, without any need for external power.


Similar danger suspected at Lake Kivu

Following the Lake Nyos disaster, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. In 2005,
Lake Kivu Lake Kivu is one of the African Great Lakes. It lies on the border between the Democratic Republic of the Congo and Rwanda, and is in the Albertine Rift, the western branch of the East African Rift. Lake Kivu empties into the Ruzizi River, which ...
in the
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, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence that outgassing events around the lake happened about every thousand years. However, a study undertaken in 2018 and released in 2020 found flaws in the 2005 study, including a possible bias in the conversion of concentrations to partial pressures, to an overestimation of concentrations, or to a problem of calibration of sensors at high pressure. The 2020 study found that when these errors were accounted for, the risk of a gas eruption at Lake Kivu did not seem to be increasing over time.


Popular culture

*In '' The Exodus Decoded'' (2006), journalist Simcha Jacobovici references the Lake Nyos disaster to explain how the Biblical plagues (such as the
Nile River The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the longest river i ...
turning into "blood", mass death of livestock, the outbreak of
boils A boil, also called a furuncle, is a deep folliculitis, which is an infection of the hair follicle. It is most commonly caused by infection by the bacterium ''Staphylococcus aureus'', resulting in a painful swollen area on the skin caused by an ...
and death of the firstborn) occurred due to the Minoan eruption at
Santorini Santorini (, ), officially Thira (, ) or Thera, is a Greek island in the southern Aegean Sea, about southeast from the mainland. It is the largest island of a small, circular archipelago formed by the Santorini caldera. It is the southern ...
circa 1600 BCE.


See also

* Lake Monoun *
List of natural disasters by death toll A natural disaster is a sudden event that causes widespread destruction, major collateral damage, or loss of life, brought about by forces other than the acts of human beings. A natural disaster might be caused by earthquakes, flooding, volcani ...


References


External links


Google Earth view of the area around Lake Nyos
{{Authority control 1986 natural disasters 1986 in Cameroon Natural disasters in Cameroon 20th-century volcanic events Gas explosions August 1986 in Africa Volcanic tsunamis 1986 disasters in Africa