Limnic eruption

A limnic eruption, also known as a lake overturn, is a rare type of natural disaster in which dissolved carbon dioxide (CO
2
) suddenly erupts from deep lake waters, forming a gas cloud capable of suffocating wildlife, livestock, and humans. A limnic eruption may also cause tsunamis as the rising CO
2
displaces water. Scientists believe earthquakes, volcanic activity, and other explosive events can serve as triggers for limnic eruptions. Lakes in which such activity occurs are referred to as limnically active lakes or exploding lakes. Some features of limnically active lakes include:

  • CO
    2
    -saturated incoming water
  • A cool lake bottom indicating an absence of direct volcanic interaction with lake waters
  • An upper and lower thermal layer with differing CO
    2
    saturations
  • Proximity to areas with volcanic activity

Investigations of the Lake Monoun and Lake Nyos casualties led scientists to classify limnic eruptions as a distinct type of disaster event, even though they can be indirectly linked to volcanic eruptions.[1]

Lake nyos
Lake Nyos shortly after a limnic eruption.

Historical occurrences

Limnic eruption is located in Cameroon
Lake Monoun
Lake Monoun
Lake Nyos
Lake Nyos
Locations of the two recorded limnic eruptions in modern history, Cameroon

Due to the largely invisible nature of the underlying cause (CO2 gas) behind limnic eruptions, it is difficult to determine to what extent eruptions have occurred in the past. In recent history, this phenomenon has been observed twice. The first recorded limnic eruption occurred in Cameroon at Lake Monoun in 1984, causing asphyxiation and death of 37 people living nearby.[2] A second, deadlier eruption happened at neighbouring Lake Nyos in 1986, this time releasing over 80 million m3 of CO2, killing around 1,700 people and 3,500 livestock, again by asphyxiation.[3]

A third lake, Lake Kivu, rests on the border between the Democratic Republic of the Congo and Rwanda, and contains massive amounts of dissolved CO2. Sediment samples from the lake taken by Professor Robert Hecky (University of Michigan) showed an event caused living creatures in the lake to go extinct around every 1000 years, and caused nearby vegetation to be swept back into the lake. Limnic eruptions can be detected and quantified on a CO2 concentration scale by taking air samples of the affected region.

The Messel pit fossil deposits of Messel, Germany, show evidence of a limnic eruption there in the early Eocene. Among the victims are perfectly preserved insects, frogs, turtles, crocodiles, birds, anteaters, insectivores, early primates, and paleotheres.

Causes

For a lake to undergo a limnic eruption, the water must be nearly saturated with gas. CO2 was the primary component in the two observed cases (Lake Nyos and Lake Monoun). In Lake Kivu, scientists are concerned about the concentrations of methane gas as well. CO2 may originate from volcanic gas emitted from under the lake or from decomposition of organic material. Before a lake is saturated, it behaves like an unopened carbonated beverage (e.g., a soft drink): the CO2 is dissolved in the water. In both the lake and the soft drink, CO2 dissolves much more readily at higher pressure (Henry's law). This is why bubbles in a can of soda form only after the can is opened; when the pressure is released, the CO2 comes out of solution. In the case of lakes, the bottom is at a much higher pressure; the deeper it is, the higher the pressure is at the bottom. Therefore, huge amounts of CO2 can be dissolved in large, deep lakes. CO2 also dissolves more readily in cooler water, such as that found at a lake bottom. A small rise in water temperature can lead to the release of a large amount of CO2.

Once a lake is saturated with CO2, it is very unstable, but a trigger is needed to set off an eruption. In the case of the 1986 Lake Nyos eruption, landslides were the suspected triggers, but a volcanic eruption, an earthquake, or even wind and rain storms are potential triggers. Another possible cause of a limnic eruption is gradual gas saturation at specific depths which can trigger spontaneous gas development.[4] For any of these cases, the trigger pushes some of the gas-saturated water higher in the lake, where pressure is insufficient to keep CO2 in solution. As bubbles start forming the water is lifted even higher in the lake (buoyancy), where yet more CO2 comes out of solution. This process forms a column of gas, at which point the water at the bottom of this column is pulled up by suction, and it, too, loses CO2 in a runaway process. This eruption discharges CO2 into the air and can displace enough water to form a tsunami.

Limnic eruptions are exceptionally rare for several reasons. First, a CO2 source must exist (regions with volcanic activity are most at risk). Second, the vast majority of lakes are holomictic (i.e., their layers mix regularly), preventing a buildup of dissolved gases. Only meromictic lakes do not mix and remain stratified, allowing CO2 to remain dissolved. It is estimated only one meromictic lake exists for every 1,000 holomictic lakes. Finally, a lake must be deep enough to have sufficient pressure to dissolve large amounts of CO2.

Consequences

Cow killed by Lake Nyos gasses
Bovine killed by the 1986 limnic eruption at Lake Nyos

Once an eruption occurs, a large CO2 cloud forms above the lake and expands to the surrounding region. Because CO2 is denser than air, it has a tendency to sink to the ground, simultaneously displacing breathable air, resulting in asphyxia. CO2 can make human bodily fluids highly acidic and potentially cause CO2 poisoning. As victims gasp for air, they actually accelerate asphyxia by inhaling CO2 gas.

At Lake Nyos, the gas cloud descended into a nearby village where it settled, killing nearly everyone; casualties as far as 25 km (16 mi) were reported. A change in skin color on some bodies led scientists to hypothesize the gas cloud may have contained dissolved acid such as hydrogen chloride, though this hypothesis is disputed.[5] Many victims were found with blisters on their skin, thought to have been caused by pressure ulcers, which were likely caused by low blood oxygen levels in those asphyxiated by carbon dioxide.[6] Nearby vegetation was largely unaffected, except any growing immediately adjacent to the lake. There, vegetation was damaged or destroyed by a 24 m (79 ft) high tsunami caused by the violent eruption.[7]

Degassing

Efforts are under way to develop a solution for removing the gas from these lakes and to prevent a build-up which could lead to another catastrophe. A team led by French scientist Michel Halbwachs began experimenting at Lake Monoun and Lake Nyos in 1990 using siphons to degas the waters of these lakes in a controlled manner.[8] The team positions a pipe vertically in the lake with its upper end above the water surface. Water saturated with CO2 enters the bottom of the pipe and rises to the top. The lower pressure at the surface allows the gas to come out of solution. Only a small amount of water must be mechanically pumped initially through the pipe to start the flow. As saturated water rises, the CO2 comes out of solution and forms bubbles. The natural buoyancy of the bubbles draws the water up the pipe at high velocity resulting in a fountain at the surface. The degassifying water acts like a pump, drawing more water into the bottom of the pipe, and creating a self-sustaining flow. This is the same process which leads to a natural eruption, but in this case it is controlled by the size of the pipe.

Each pipe has a limited pumping capacity and several would be required for both Lake Monoun and Lake Nyos to degas a significant fraction of the deep lake water and render the lakes safe. The deep lake waters are slightly acidic due to the dissolved CO2 which causes corrosion to the pipes and electronics, necessitating ongoing maintenance. There is some concern CO2 from the pipes could settle on the surface of the lake forming a thin layer of unbreathable air and thus potentially causing problems for wildlife.

In January 2001, a single pipe was installed by the French-Cameroonian team on Lake Nyos, and two more pipes were installed in 2011 with funding support from the United Nations Development Programme.[9][10] A pipe was installed at Lake Monoun in 2003 and two more were added in 2006.[9][10] These three pipes are thought to be sufficient to prevent an increase in CO2 levels, removing approximately the same amount of gas that naturally enters at the lake bed. In January 2003, an 18-month project was approved to fully degas Lake Monoun,[11] and the lake has since been rendered safe.[9]

Lake Kivu's potential dangers

LakeKivu satellite
Satellite image of Lake Kivu.

Lake Kivu is not only 2,000 times larger than Lake Nyos, but is also located in a far more densely populated area, with over two million people living along its shores, and the part within the Democratic Republic of the Congo is a site of active armed conflict and low state capacity for the DRC government. Lake Kivu has not reached a high level of CO2 saturation yet; if the water were to become heavily saturated, a limnic eruption would pose a great risk to human and animal life. Two significant changes in Lake Kivu's physical state have brought attention to a possible limnic eruption: the high rates of methane dissociation and a rising surface temperature.[12] Research investigating historical and present-day temperatures show Lake Kivu's surface temperature is increasing by about 0.12 °C per decade.[12] Lake Kivu is in close proximity to potential triggers: Mount Nyiragongo (an active volcano which erupted in January 2002), an active earthquake zone, and other active volcanoes.

While the lake could be degassed in a manner similar to Lake Monoun and Lake Nyos, due to the size of Lake Kivu and the volume of gas it contains, such an operation would be expensive, running into the millions of dollars. A scheme initiated in 2010 to use methane trapped in the lake as a fuel source to generate electricity in Rwanda has led to a degree of CO2 degassing.[13] During the procedure for extracting the flammable methane gas used to fuel power stations on the shore, some CO2 is removed in a process known as catalyst scrubbing. It is unclear whether enough gas will be removed to eliminate the danger of a limnic eruption at Lake Kivu.

See also

References

  1. ^ Volcanic Lakes and Gas Releases USGS/Cascades Volcano Observatory, Vancouver, Washington.
  2. ^ Sigurdsson, H.; Devine, J.D.; Tchua, F.M.; Presser, F.M.; Pringle, M.K.W.; Evans, W.C. (1987). "Origin of the lethal gas burst from Lake Monoun, Cameroun". Journal of Volcanology and Geothermal Research. 31 (1–2): 1–16. Bibcode:1987JVGR...31....1S. doi:10.1016/0377-0273(87)90002-3.
  3. ^ Kling, George W.; Clark, Michael A.; Wagner, Glen N.; Compton, Harry R.; Humphrey, Alan M.; Devine, Joseph D.; Evans, William C.; Lockwood, John P.; et al. (1987). "The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa". Science. 236 (4798): 169–75. Bibcode:1987Sci...236..169K. doi:10.1126/science.236.4798.169. PMID 17789781.
  4. ^ Tassi, Franco (2014). "An overview of the structure, hazards, and methods of investigation of Nyos-type lakes from the geochemical perspective". Journal of Limnology. 73 (1). doi:10.4081/jlimnol.2014.836 – via EBSCO host.
  5. ^ Freeth, SJ (1989). "Lake Nyos disaster". BMJ. 299 (6697): 513. doi:10.1136/bmj.299.6697.513-a. PMC 1837334. PMID 2507040.
  6. ^ BBC Horizon programme "Killer Lakes"
  7. ^ Gusiakov, V.K. (2014). "Tsunami impact on the African continent: historical cases and hazard evaluation". In Ismail-Zadeh, A.; Urrutia Fucugauchi, J.; Kijko, A.; Takeuchi, K.; Zaliapin, I. (editors) (eds.). Extreme Natural Hazards, Disaster Risks and Societal Implications. Cambridge: Cambridge University Press. p. 230. ISBN 978-1-107-03386-3.CS1 maint: uses editors parameter (link)
  8. ^ *BBC Cameroons "killer lake" degassed
  9. ^ a b c Jones, Nicola (2010). "Battle to degas deadly lakes continues". Nature. 466 (7310): 1033. doi:10.1038/4661033a. PMID 20739980.
  10. ^ a b Nasr, Susan (24 March 2009). "How did Lake Nyos suddenly kill 1,700 people?". HowStuffWorks.com. Retrieved 18 April 2013.
  11. ^ Nicola Jones (1 February 2003). "Lake to lose its silent killer". newscientist. Retrieved 2009-08-20.
  12. ^ a b Katsev, Sergei (2014). "Recent Warming of Lake Kivu". PLOS ONE. 9 (10): e109084. Bibcode:2014PLoSO...9j9084K. doi:10.1371/journal.pone.0109084. PMC 4189960.
  13. ^ Rice, Xan (16 August 2010). "Rwanda harnesses volcanic gases from depths of Lake Kivu". The Guardian. London.

External links

Asphyxiant gas

An asphyxiant gas is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation). Because asphyxiant gases are relatively inert and odorless, their presence in high concentration may not be noticed, except in the case of carbon dioxide (hypercapnia).

Toxic gases, by contrast, cause death by other mechanisms, such as competing with oxygen on the cellular level (e.g. carbon monoxide) or directly damaging the respiratory system (e.g. phosgene). Far smaller quantities of these are deadly.

Notable examples of asphyxiant gases are methane, nitrogen, argon, helium, butane and propane. Along with trace gases such as carbon dioxide and ozone, these compose 79% of Earth's atmosphere.

Brosno dragon

The Brosno dragon, also known as Brosnya (Russian: Бросня), is a lake monster which in Russian folklore is said to inhabit Lake Brosno, near Andreapol in western Russia. It is described as resembling a dragon and is the subject of a number of regional legends, some which are said to date back to the 13th century.

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 gases from solvents when the compounds they are working on are possibly air- or oxygen-sensitive (air-free technique), or when bubble formation at solid-liquid interfaces becomes a problem. The formation of gas bubbles when a liquid is frozen can also be undesirable, necessitating degassing beforehand.

Disaster

A disaster is a serious disruption occurring over a relatively short period of time that causes widespread human, material, economic or environmental loss which exceeds the ability of the affected community or society to cope on a timely basis

using its own resources. Developing countries suffer the greatest costs when a disaster hits – more than 95 percent of all deaths caused by hazards occur in developing countries, and losses due to natural hazards are 20 times greater (as a percentage of GDP) in developing countries than in industrialized countries.

Goma

Goma is the capital of North Kivu province in the eastern Democratic Republic of the Congo. It is located on the northern shore of Lake Kivu, next to the Rwandan city of Gisenyi. The lake and the two cities are in the Albertine Rift, the western branch of the East African Rift system. Goma lies only 13–18 km (8.1–11.2 mi) south of the active Nyiragongo Volcano. The recent history of Goma has been dominated by the volcano and the Rwandan Genocide of 1994, which in turn fuelled the First and Second Congo Wars. The aftermath of these events was still having effects on the city and its surroundings in 2010. The city was captured by rebels of the March 23 Movement during the M23 rebellion in late 2012, but has since been retaken by government forces.

A pastor infected during the ongoing 2018–19 Kivu Ebola epidemic in the region was found in mid-July 2019 to have travelled to Goma.

Lac Pavin

Lac Pavin is a meromictic crater lake located in the Puy-de-Dôme department of France, between Besse-en-Chandesse and Super-Besse. It gives its name to a cheese: Pavin cheese.

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 flows southwards into Lake Tanganyika.

Lake Monoun

Lake Monoun is a lake in West Province, Cameroon, that lies in the Oku Volcanic Field 5.58°N 10.59°E / 5.58; 10.59. On August 15, 1984, the lake exploded in a limnic eruption, which resulted in the release of a large amount of carbon dioxide that killed 37 people. At first, the cause of the deaths was a mystery, 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.

Lake Nyos

Lake Nyos 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 the lake and leaks carbon dioxide (CO2) into the water, changing it into carbonic acid. Nyos is one of only three known exploding lakes to be saturated with carbon dioxide in this way, 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 a large cloud of CO2, which suffocated 1,746 people and 3,500 livestock in nearby towns and villages. 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 natural levée 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 disaster

On 21 August 1986, a limnic eruption at Lake Nyos in northwestern Cameroon killed 1,746 people and 3,500 livestock.

The eruption triggered the sudden release of about 100,000–300,000 tons (1.6 million tons, according to some sources) of carbon dioxide (CO2). The gas cloud initially rose at nearly 100 kilometres per hour (62 mph) and then, being heavier than air, descended onto nearby villages, displacing all the air and suffocating people and livestock within 25 kilometres (16 mi) of the lake.A degassing system has since been installed at the lake, with the aim of reducing the concentration of CO2 in the waters and therefore the risk of further eruptions.

Lake stratification

Lake stratification is the separation of lakes into three layers:

Epilimnion: the top of the lake.

Metalimnion (or thermocline): the middle layer, which may change depth throughout the day.

Hypolimnion: the bottom layer.The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water's density with temperature. Cold water is denser than warm water and the epilimnion generally consists of water that is not as dense as the water in the hypolimnion. However, the temperature of maximum density for freshwater is 4 °C. In temperate regions where lake water warms up and cools through the seasons, a cyclical pattern of overturn occurs that is repeated from year to year as the cold dense water at the top of the lake sinks. For example, in dimictic lakes the lake water turns over during the spring and the fall. This process occurs more slowly in deeper water and as a result, a thermal bar may form. If the stratification of water lasts for extended periods, the lake is meromictic.

In shallow lakes, stratification into epilimnion, metalimnion, and hypolimnion often does not occur, as wind or cooling causes regular mixing throughout the year. These lakes are called polymictic. There is not a fixed depth that separates polymictic and stratifying lakes, as apart from depth, this is also influenced by turbidity, lake surface area, and climate.The lake mixing regime (e.g. polymictic, dimictic, meromictic) describes the yearly patterns of lake stratification that occur during most of the years. However, short-term events can influence lake stratification as well. Heat waves can cause periods of stratification in otherwise mixed, shallow lakes, while mixing events such as storms or large river discharge, can break down stratification.The accumulation of dissolved carbon dioxide in three meromictic lakes in Africa (Lake Nyos and Lake Monoun in Cameroon and Lake Kivu in Rwanda) is potentially dangerous because if one of these lakes is triggered into limnic eruption, a very large quantity of carbon dioxide can quickly leave the lake and displace the oxygen needed for life by people and animals in the surrounding area.

Natural resource and environmental managers are often challenged by problems caused by lake and pond thermal stratification. Fish die-offs have been directly associated with thermal gradients, stagnation, and ice cover. Excessive growth of plankton may limit the recreational use of lakes and the commercial use of lake water. With severe thermal stratification in a lake, the quality of drinking water also can be adversely affected. For fisheries managers, the spatial distribution of fish within a lake is often adversely affected by thermal stratification and in some cases may indirectly cause large die-offs of recreationally important fish. One commonly used tool to reduce the severity of these lake management problems is to eliminate or lessen thermal stratification through aeration. Many types of aeration equipment have been used to thermally destratify lakes. Aeration has met with some success, although it has rarely proved to be a panacea.Lake mixing regimes can shift in response to increasing air temperatures. Some dimictic lakes can turn into monomictic lakes, while some monomictic lakes might become meromictic, as a consequence of rising temperatures.

Mazuku

In geology, a mazuku (Swahili: 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 heavier than air, which causes it to flow downhill, hugging the ground like a low fog, and is also undetectable by human olfactory or visual senses in most conditions.

Mazuku can be related to volcanic activity or to a natural disaster known as a limnic eruption. In the first case, noxious gases are released from the Earth's crust into the atmosphere, whereas in the second case the gases originate deep in a lake and boil rapidly to the surface. Because of their nature as sporadic and subtle events, few mazuku have been recorded, but there is a growing understanding of them based on historical and fossil evidence.

Natural disaster

A natural disaster is a major adverse event resulting from natural processes of the Earth; examples are floods, hurricanes, tornadoes, volcanic eruptions, earthquakes, tsunamis, and other geologic processes. A natural disaster can cause loss of life or damage property, and typically leaves some economic damage in its wake, the severity of which depends on the affected population's resilience (ability to recover) and also on the infrastructure available.An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population. In a vulnerable area, however, such as Nepal during the 2015 earthquake, an earthquake can have disastrous consequences and leave lasting damage, which can require years to repair.

Pockmark (geology)

Pockmarks are craters in the seabed caused by fluids (gas and liquids) erupting and streaming through the sediments.

Pockmarks were discovered off the coasts of Nova Scotia, Canada in the late 1960s by Lew King and Brian McLean of the Bedford Institute of Oceanography. Pockmarks are uncommon on the land surface, and are expected in the ocean.

They were discovered off Nova Scotia, using a new side scan sonar developed in the late 1960s by Kelvin Hughes.

The craters off Nova Scotia are up to 150 m (490 ft) in diameter and 10 m (33 ft) deep. Pockmarks have been found worldwide. Discovery was aided by the use of high-resolution multibeam acoustic systems for bathymetric mapping. In these cases, pockmarks have been interpreted as the morphological expression of gas or oil leakage from active hydrocarbon system or a deep overpressured petroleum reservoir.

Protopsephurus

Protopsephurus is an extinct genus of paddlefish which existed in China during the Barremian age to the Aptian age of the Early Cretaceous period. It contains the species Protopsephurus liui, which was measured to be up to be one meter in length.

The Exodus Decoded

The Exodus Decoded is a documentary film aired April 16, 2006 on The History Channel. The program was created by Israeli-Canadian filmmaker Simcha Jacobovici and producer/director James Cameron. (The two would later work together on The Lost Tomb of Jesus.) The documentary explores the supposed evidence for the Biblical account of the Exodus. Its claims and methods were criticized by Biblical scholars and mainstream scientists.Jacobovici suggests that the Exodus took place around 1500 BC, during the reign of pharaoh Ahmose I, and that it coincided with the Minoan eruption. In the documentary, the plagues that ravaged Egypt in the Bible are explained as having resulted from that eruption and a related limnic eruption in the Nile Delta, similar to what occurred in the 1980s at Lake Nyos in Cameroon. While much of Jacobovici's archaeological evidence for the Exodus comes from Egypt, some comes from Mycenae on mainland Greece, such as a gold ornament that somewhat resembles the Ark of the Covenant.

The documentary makes extensive use of computer animation and visual effects made by Gravity Visual Effects, Inc., based in Toronto. It runs for 90 minutes and was first aired in Canada on April 16, (Easter Day) 2006 (Discovery Channel Canada). Shown in the US on August 20, 2006 (History Channel US), UK on December 23, 2006 (Discovery Channel UK), Spain on December 25, 2006 (Cuatro) and Israel on April 3, 2007 (Channel 2).

Vulcanobatrachus

Vulcanobatrachus is an extinct genus of fossil frog. The new genus which contains the single species Vulcanobatrachus mandelai found at Marydale, South Africa was recently described. The genus owes its name to the fact that fossils were recovered from an extinct volcanic crater lake of Late Cretaceous origin. The fossil frogs are assumed to have died following a limnic eruption (a degassing event possibly of CO2) by the volcano.

The existence of fossil specimens was discovered accidentally in the late 1970s during prospecting of the volcanic kimberlite pipe for diamonds by de Beers Mining Company. Specimens of Vulcanobatrachus mandelai are curated by Iziko Museums, Gardens, Cape Town.

Wum

Wum is a town and commune in Cameroon. It is the capital of Menchum division in the Northwest Province.

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