Lake Monoun is a crater lake (
maar) in
West Province, Cameroon
The West Region (french: Région de l'Ouest) is 14,000 km2 of territory located in the central-western portion of the Republic of Cameroon. It borders the Northwest Region to the northwest, the Adamawa Region to the northeast, the Centre ...
, that lies in the
Oku Volcanic Field Oku or OKU may refer to:
*Oku, Cameroon, subdivision in the Northwest Region of Cameroon
** Lake Oku, a crater lake on the Bamenda Plateau in the Northwest Region of Cameroon
** Mount Oku, the largest volcano in the Oku Massif, in the Cameroon Volc ...
. On August 15, 1984, a
limnic eruption
A limnic eruption, also known as a lake overturn, is a very rare type of natural disaster in which dissolved carbon dioxide () suddenly erupts from deep lake waters, forming a gas cloud capable of suffocating wildlife, livestock, and humans. A lim ...
occurred at the lake, which resulted in the release of a large amount of
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
() that killed 37 people. At first, the deaths remained unexplained, and causes such as terrorism were suspected. Further investigation and
a similar event two years later at Lake Nyos led to the currently accepted explanation.
Disaster
![Monoun](https://upload.wikimedia.org/wikipedia/commons/6/65/Monoun.jpg)
Several people reported hearing a loud noise on August 15, 1984, around 22:30. A gas cloud reportedly emanated from a crater in the eastern part of the lake. The resulting deaths of residents in a low-lying area are believed to have occurred between 03:00 and dawn. The victims were said to have
skin burns, which reports later clarified as "skin damage" such as discoloration. Survivors reported that the whitish, smoke-like cloud smelled bitter and acidic. Vegetation was flattened around the eastern part of the lake, probably by a large wave of up to height.
Although Lake Monoun is near the center of a
volcanic field
A volcanic field is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes ...
that includes at least 34 recent craters, the subsequent investigation found that the event was not caused by an eruption or sudden ejection of volcanic gas from the lake. Rather, emission of carbon dioxide in a limnic eruption is thought to be to blame. The cloud's smell and skin damage to victims were not fully explained. Some theories attribute the skin problems to a combination of preexisting conditions and routine postmortem effects like
livor mortis
Livor mortis (Latin: ''līvor'' – "bluish color, bruise", ''mortis'' – "of death"), postmortem lividity (Latin: ''postmortem'' – "after death", ''lividity'' – "black and blue"), hypostasis (Greek: ὑπό, ''hypo'', meaning "under, bene ...
, another medical interpretation says the body's metabolic rate was reduced inducing a severely restricted circulation in
capillary vessels of the skin, resulting in
necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
,
although there is no clear consensus.
Among the victims were some of the riders in a truck carrying twelve people. The truck's engine stopped working as it became starved of oxygen, and the people inside the truck got out and were killed. Two people sitting on top of the truck survived, because their elevated position allowed them to breathe – carbon dioxide is heavier than air (oxygen and nitrogen) which causes it to stay close to the ground.
Two years later, on 21 August 1986, a similar and even more deadly event occurred at
Lake Nyos
Lake Nyos ( ) is a crater lake in the Region of Cameroon, located about 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 ...
, about north-northwest, killing 1,746 people and more than 3,000 livestock.
Along with Lake Nyos and
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, whic ...
, Lake Monoun is one of three lakes in the world known to have high concentrations of gas dissolved deep below the surface and which have the right conditions for a limnic eruption.
Degassing
In March and April 1992 preliminary test were conducted at Lake Monoun using the
gas lift
Gas lift or bubble pumps use the artificial lift technique of raising a fluid such as water or oil by introducing bubbles of compressed air, water vapor or other vaporous bubbles into the outlet tube. This has the effect of reducing the hydrosta ...
method as known in the petroleum industry. Initially a pump (or preferably a compressed gas injection) is needed to pull water from the bottom, but as carbon dioxide begins to come out of
solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Soluti ...
it creates
buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
in the water in the pipes, allowing a self-sustaining process without the need for external energy supply. Due to the very limited funds for the project and construction basically by hand, the solution was the use of
high-density polyethylene
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...
(HDPE) pipes. The material has a specific gravity of 0.96 kg/L which means an almost neutral buoyancy in water. The HDPE plastic is flexible, not brittle, and resistive to chemical and weathering alteration as proven material for natural gas distribution networks. Nevertheless, the CO
2-rich, oxygen-depleted water from the depth is a challenge for steel fittings as
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
occurred, forming
siderite
Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...
and eating away iron. The pipe could be easily solded electrically in the field from standard segments, and deployed with just the help of a few rubber boats plus floats. With some
ballast
Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
, the pipe hangs freely from an anchored raft like a pendulum.
In February 2003, a venting pipe was inserted into the lake, in an effort to prevent the disaster from recurring. In the initial
degassing
Degassing, also known as degasification, is the removal of dissolved gases from liquids, especially water or aqueous solutions. There are numerous methods for removing gases from liquids.
Gases are removed for various reasons. Chemists remove ga ...
phase, an fountain developed from the water tapped at depth.
However, a study found in 2005 that gas was not being removed from the lake quickly enough to ensure that the disaster never happens again. It was recommended to lower the inlet of the existing pipe down to and the addition of a second pipe in order to release more carbon dioxide.
On the other hand, the deep lake water is rich in
iron(II)
In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+.
The adjective ferrous or the prefix ferro- is often used to s ...
ions, which after a while transforms into
limonite
Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxid ...
. As the lake is a fishing ground for local villagers, the effect of a higher iron intake rate in the upper water layer on fishlife needed consideration before scaling up the degassing rate.
In December 2013, the degassing pipe, which has lost its self-lift capability due to the bubbling effect in the riser as a significant amount of CO
2 had been removed from the bottom layers, was upgraded with a small solar-power driven rotary pump. This system has the capability to lift ca. 100 m
3 of bottom water to the surface per day. Nevertheless, the degassing capability is less than the natural inflow of CO
2-rich water, therefore two more of these solar pumps are needed to avoid a long-term build up of higher and dangerous levels of CO
2 in the stratified water levels.
See also
*
Mazuku
In geology, a mazuku ( Swahili for "evil wind") is a pocket of carbon dioxide-rich air that can be lethal to any human or animal life inside. Mazuku are created when carbon dioxide accumulates in pockets low to the ground. CO2 is denser than air, w ...
*
Meromictic lake
A meromictic lake is a lake which has layers of water that do not intermix. In ordinary, holomictic lakes, at least once each year, there is a physical mixing of the surface and the deep waters.
The term ''meromictic'' was coined by the Austr ...
*
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, whic ...
*
Limnic eruption
A limnic eruption, also known as a lake overturn, is a very rare type of natural disaster in which dissolved carbon dioxide () suddenly erupts from deep lake waters, forming a gas cloud capable of suffocating wildlife, livestock, and humans. A lim ...
References
*
External links
The Lake Nyos and Monoun Degassing ProjectKiller lakes in Cameroon may strike again– Reports from the investigation of the disaster
BBC News 27 Sep 2005: Action needed on deadly lakesMechanics of the switching on of the trigger mechanism of limnological catastrophes–
Latvia
Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...
n research by Nataliya Anatolievna Solodovnik and Anatoliy Borisovich Solodovnik
{{DEFAULTSORT:Monoun
Lakes of Cameroon
West Region (Cameroon)
20th-century volcanic events
Mbéré Rift Valley
Rift volcanoes
Volcanoes of Cameroon
Maars of Cameroon
Gas explosions
Volcanic crater lakes
Meromictic lakes
Explosions in Cameroon
Explosions in 1984
August 1984 events in Africa
1984 in Cameroon
Natural disasters in Cameroon
Limnically active lakes