Being a very rare and bizarre occurrence in nature, there are 3 known exploding lakes in the world, dubbed the “African Lakes of Death” — Lake Nyos, Lake Kivu, and Lake Monoun.
There are weak spots in the earth’s crust in Cameroon, Africa, where magma — liquid rock — rises from the earth’s mantle. The magma shoots up quickly and vertically, cutting a tube towards the surface. If it hits wet rock as it rises it explodes, blasting a crater in the ground, then water fills the craters and they become lakes. This is how Lake Monoun was formed over 18,000 years ago, and Lake Nyos about 400 years ago.
Lake Nyos
Lake Nyos is a crater lake in the Northwest Region of Cameroon, about 200 miles (322 km) northwest of Yaoundé. It’s a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity, and a natural dam of volcanic rock hems in the lake’s waters.
Exploding Lake Nyos.
A pocket of magma lies beneath the lake and leaks carbon dioxide into the water, changing it into carbonic acid.
The lake suddenly exploded, emitting a massive cloud of about 1.6 million tons of CO2 on August 21, 1986, which suffocated 1,700 people and 3,500 livestock in nearby villages. Though not entirely unprecedented, it was the first known large-scale asphyxiation caused by a natural event.
It was reported that farmers living near the lake heard rumbling just as a foamy spray shot hundreds of feet out of the lake — known as a limnic eruption — rising at about 62 mph (100 km/h) and a massive white cloud collected over the water growing to 328 feet (100 meters) tall and flowed across the land. When people near the lake went to investigate the noise, they lost consciousness.
The gas spilled over the northern lip of the lake into a valley running from Cha to Subum, and then rushed down 2 valleys branching off it to the north, as the monstrous cloud channelled it into settlements causing inhabitants in the area to collapse within a few breaths of the deadly gases. The worst affected villages were Cha, Nyos, and Subum. All but 4 people on high ground died in Nyos and Kam — the first villages hit by the cloud.
The valley split and the cloud followed, killing people up to 15.5 miles (25 kilometers) away from the Lake Nyos. Bodies and cattle were found lying on the ground in the valley when the cloud began to dissipate 2 days later. Some revived after being unconscious for up to 36 hours to find their family, neighbors, and livestock all dead.
The lake had also changed — it was shallower and its formerly picturesque blue hue had turned to a deep rust color. It’s believed that about 1.2 cubic kilometers (0.29 cu mi) of gas 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 oxidized by the air. The level of the lake dropped by about a meter and trees near the lake were knocked down.
Exploding Lake Nyos as it appeared less than 2 weeks after the eruption on August 29, 1986. Areas once covered with water are especially visible around the shore of the lake.
Scientists concluded from evidence that a 300-foot (91 m) 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 a wave of at least 80 feet (24 m) that would scour the shore of one side.
It’s believed that many of the victims had been poisoned by a mixture of gases including hydrogen and sulfur gases. Poisoning by these gases would lead to burning pains in the eyes and nose, coughing and signs of asphyxiation similar to being strangled, as like ‘being gassed by a kitchen stove.’
Following the disaster, the lake was dubbed the “Deadliest Lake” by Guinness World Records in 2008.
One survivor, Joseph Nkwain from Subum, described the distaster when he awoke after the gases had struck:
“I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible.”
“I heard my daughter snoring in a terrible way, very abnormal. When crossing to my daughter’s bed I collapsed and fell. I was there till 9 o’clock in the (Friday) morning until a friend of mine came and knocked at my door.”
“I was surprised to see that my trousers were red, had some stains like honey. I saw some starchy mess on my body. My arms had some wounds. I didn’t really know how I got these wounds”
“I opened the door. I wanted to speak, my breath would not come out.”
“My daughter was already dead. I went into my daughter’s bed, thinking that she was still sleeping. I slept till it was 4:30 p.m. in the afternoon on Friday.”
“(Then) I managed to go over to my neighbors’ houses. They were all dead. I decided to leave (because) most of my family was in Wum.”
“I got my motorcycle. A friend whose father had died left with me (for) Wum. As I rode through Nyos I didn’t see any sign of any living thing. (When I got to Wum), I was unable to walk, even to talk. My body was completely weak.”
Exploding Lake Nyos, silty after the limnic eruption.
Being about 1.5 times as dense as air, carbon dioxide caused the cloud to ‘hug’ the ground and descend down the valleys where various villages were located. The mass was about 164 feet (50 meters) thick and it traveled downward at a rate of 12 to 31 mph (20 to 50 km/h). For roughly 14 miles (23 kms) the cloud remained condensed and dangerous, suffocating many of the people sleeping in Nyos, Kam, Cha, and Subum.
A change in skin color on some bodies led scientists to think that the gas cloud may have contained a dissolved acid such as hydrogen chloride as well, but that hypothesis is disputed. Many victims were found with blisters on their skin. This is believed to have been caused by pressure ulcers, which likely formed from the low levels of oxygen present in the blood of those asphyxiated by the carbon dioxide.
Thousands of cattle and wild animals were also asphyxiated, but no official counts were made. Vegetation nearby was mostly unaffected except for that which grew immediately adjacent to the lake which was damaged or destroyed by a 16.4 foot (5-meter) tsunami from the violent eruption.
About 4,000 inhabitants fled the area, and many of these developed respiratory problems, lesions, and paralysis as a result of the gases.
A cow suffocated by gases from Lake Nyos
Cattle suffocated by CO2 at Lake Nyos.
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 about 400 years ago, and is 5,900 feet (1,800 meters) across and 682 feet 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 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 50 miles (80 km) directly below the lake resides a pool of magma, which lets off carbon dioxide and other gases and the gasses then travel upward through the earth.
The fumes are then ensnared by the natural springs encircling the lake, ultimately rising to the surface of the water and leading into the lake. This was the cause for the presence of carbon dioxide and other gases contained within the lake.
The lake waters are held in place by a natural dam composed of volcanic rock. At its narrowest point, the wall measures 130 feet (40 meters) high and 148 feet (45 meters) wide.
It’s unknown 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.
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 CO2 to effervesce out of solution.
Additional Threats of Weakening Dam
The lake also poses a threat today due to its weakening natural wall. A geological tremor could cause this natural dike to give way, allowing water to rush into downstream villages all the way into Nigeria and allowing much carbon dioxide to escape.
French scientists working on degassing Lake Nyos.
On August 18, 2005, Dr. Isaac Njilah, a geologist at the University of Yaoundé, suggested that 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 cause the lake wall to give way, resulting in up to1.8 billion cubic feet (50 million cu m) of water flooding downhill into areas of the Northwest Province and the Nigerian states of Taraba and Benue. Dr. Njilah estimates that the area is home to more than 10,000 people.
The Cameroonian government 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 the dam over 3 days in September 2005 and confirmed that the natural lip had weakened. Van Duin believed that the dam would breach within the next 10 or 20 years.
One possible means of averting the 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 was lowered by about 66 feet (20 m), the pressure on the wall would be reduced significantly.
Lake Kivu
As one of the African Great Lakes and one of the 3 ‘erupting lakes,’ Lake Kivu is only a stone’s throw away from Nyurangongo volcano, with thousands of years worth of dissolved volcanic gases trapped in its waters.
Exploding Lake Kivu shore at Gisenyi.
Surrounded by majestic mountains, it’s situated on the border between the Democratic Republic of the Congo and Rwanda, and is in the Albertine (western) Rift, a part of the Great Rift Valley that’s slowly being pulled apart, causing volcanic activity in the area, and making it particularly deep. Its maximum depth of 1575 feet (480 m) is ranked 15th in the world.
The world’s 10th-largest inland island, Idjwi, lies in Lake Kivu, as well as the tiny island of Tshegera, which also lies within the boundaries of Virunga National Park.
Lake Kivu’s Potential Danger
Lake Kivu is not only 2,000 times larger than Lake Nyos — it’s also located in a far more densely populated area, with over 2 million people living along its shores. Fortunately, it hasn’t reached a high level of CO2 saturation, yet.
Exploding Lake Kivu.
If the water were to become heavily saturated, it could become an even greater risk to human and animal life, since it’s located very close to a potential trigger — Mount Nyiragongo, an active volcano that erupted in January 2002. It’s also located in an active earthquake zone and close to other active volcanoes.
Analysis of Lake Kivu’s geological history indicates sporadic massive biological extinction on millennial timescales. The trigger for violent lake overturns in Lake Kivu’s case is unknown but volcanic activity is suspected. The gaseous chemical composition of exploding lakes is unique to each lake — in Lake Kivu’s case, methane and carbon dioxide due to lake water interaction with a volcano.
There is an estimated 256 cubic kilometers of carbon dioxide. The methane is reported to be produced by microbial reduction of the volcanic CO2.
The risk from a possible Lake Kivu overturn would be catastrophic, dwarfing other documented lake overturns at Lakes Nyos and Monoun, due to the millions of people living in the lake basin.
Exploding Lake Kivu, African lakes of death.
Cores from the Bukavu Bay area of the lake reveal that the bottom has layered deposits of the rare mineral monohydrocalcite interlain with diatoms, on top of sapropelic sediments with high pyrite content which are found at 3 different intervals. The sapropelic layers are believed to be related to hydrothermal discharge and the diatoms to a bloom which reduced the carbon dioxide levels low enough to precipitate monohydrocalcite.
Scientists hypothesize that sufficient volcanic interaction with the lake’s bottom water that has high gas concentrations would heat water, force the methane out of the water, spark a methane explosion, and trigger a nearly simultaneous release of carbon dioxide.
The carbon dioxide would then suffocate massive numbers of people in the lake basin as the gases roll off the lake surface. It’s also possible that the lake could spawn lake tsunamis as gas explodes out of it.
The risk posed by Lake Kivu began to be understood during the analysis of more recent events at Lake Nyos. Lake Kivu’s methane was originally thought to be merely a cheap natural resource for export, and for the generation of cheap power. Once the mechanisms that caused lake overturns began to be understood, so did awareness of the risk the lake posed to the local population.
Methane Extraction for Power Resource
Lake Kivu has recently been found to contain approximately 72 billion cubic yards (55 billion cu m) of dissolved methane gas at a depth of 1,000 feet (300 m) — if burnt over 1 year, it would give an average power of about 100 gigawatts.
Exploding Lake Kivu.
Until 2004, extraction of the gas was done on a small scale, with the extracted gas being used to run boilers at the Bralirwa brewery in Gisenyi.
As far as large-scale exploitation of this resource is concerned, the Rwandan government is in negotiations with a number of parties to produce methane from the lake. Extraction is said to be cost-effective and simple because once the gas-rich water is pumped up, the dissolved gases — primarily carbon dioxide, hydrogen sulphide and methane — begin to bubble out as the water pressure gets lower.
This project is expected to increase Rwanda’s energy generation capability by as much as 20 times and will enable Rwanda to sell electricity to neighboring African countries.
A problem associated with the prevalence of methane is that of mazuku — a pocket of oxygen-poor air that can be lethal to any human or animal life inside. The term comes from Swahili and means ‘evil wind.’
The beach on Lake Kivu at Gisenyi, Rwanda.
Shore at Gisenyi on Lake Kivu.
Mazukus are created when an odorless and invisible gas such as carbon dioxide accumulates in pockets low to the ground. CO2 is heavier than air which causes it to stay close to the ground, and is also undetectable by human olfactory or most visual conditions.
The first European to visit the lake was German Count Adolf von Götzen in 1894. Since then it’s been caught up in the conflict between Hutu and Tutsi people in Rwanda, and their allies in DR Congo, which led to the 1994 Rwandan Genocide and the First and Second Congo Wars. Lake Kivu gained notoriety as a place where many of the victims of the genocide were dumped.
Exploding Lake Monoun
On August 15, 1984, the Lake Monoun exploded in a limnic eruption, which resulted in the release of a large amount of carbon dioxide that killed 37 local residents. The cause of the deaths was a mystery at first, and reasons such as terrorism were suspected. Further investigation and the similar event 2 years later at Lake Nyos led to the currently accepted explanation.
Exploding Lake Monoun.
Several people reported hearing a loud noise that night around 10:30pm. 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 3:00am 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 tsunami.
Being located in West Province, Cameroon, that lies in the Oku Volcanic, while the lake is near the center of a volcanic field 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.
It’s believed that emission of carbon dioxide in a limnic eruption is 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, although there is no clear consensus.
Exploding Lake Monoun.
Exploding Lake Monoun.
Among the victims were some of the riders in a truck carrying 12 people. The truck’s engine stopped working, and the people inside the truck got out and were killed. However, 2 people sitting on top of the truck survived because their elevated position allowed them to breathe.
Lake Quilotoa
There is also Lake Quilotoa in Ecuador which is rich in CO2, very deep, and in a tropical climate. Some scientists consider it a potential analog of Lake Nyos.
Lake Quilotoa.
Quilotoa is a water-filled caldera and the westernmost volcano in the Ecuadorian Andes. The 2-mile (3 km) wide caldera was formed by the collapse of a dacite volcano following a catastrophic VEI-6 eruption about 800 years ago, which produced pyroclastic flows and lahars that reached the Pacific Ocean, and spread an airborne deposit of volcanic ash throughout the northern Andes.
The caldera has since accumulated an 820 foot (250 m) deep crater lake, which has a greenish color as a result of dissolved minerals. Fumaroles are found on the lake floor and hot springs occur on the eastern flank of the volcano.
Quilotoa is a tourist site of growing popularity. The route to the summit — the small town of Quilotoa — is generally traveled by hired truck or bus from the town of Zumbahua 17 km to the South.
A number of simple hostels have developed in the immediate area, and offer services such as mules and guides for the 5-hour hike around the caldera, a half-hour hike down and 1-2 hour hike back up the 400 meter vertical ascent, and very basic lodging down in its bowl. Camping is permitted at the bottom of the crater, but there is no potable water other than half-liter bottles sold at the hostel, and only a single pit toilet, located in the hostel.
Lake Quilotoa.
Lake Quilotoa.
Road between Zumbahua and Lake Quilotoa.
Degassing Lakes
To prevent a repetition of these disasters, efforts have been under way for several years to develop a solution to remove the gas from these lakes and prevent a build-up that could lead to another catastrophe. A team of French scientists began experimenting at Lake Monoun and Lake Nyos in 1990 using siphons to degas the waters in a controlled manner, though additional tubes are needed to make the lake safe.
Lake Nyos.
A pipe is positioned vertically in the lake with its upper end above the water’s 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.
Interestingly, only a small amount of water has to initially be mechanically pumped through the pipe to start the flow. As the 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 causing a large fountain at the surface.
The degassifying water acts as a pump, drawing more water into the bottom of the pipe, and creating a self-sustaining flow. This is the same process that leads to a natural eruption, but in this case it’s 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 are also fears that the CO2 from the pipes could settle on the surface of the lake forming a thin layer of unbreathable air and thus causing problems for wildlife.
In January 2001, a single pipe was installed on Lake Nyos. A 2nd pipe was installed at Lake Monoun in late 2002. These 2 pipes are thought to be sufficient to prevent an increase in CO2 levels, removing approximately the same amount of gas as that naturally entering at the lake bed. In January 2003, an 18-month project had been given approval to fully degas Lake Monoun, but appears to have been subsequently cancelled.
Degassing Lake Nyos.
The scale of the disaster led to much study on how a recurrence could be prevented. Estimates of the rate of carbon dioxide entering the Lake Nyos suggested that outgassings could occur every 10 to 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.
Following the Lake Nyos tragedy, scientists investigated other African lakes to see if a similar phenomenon could happen elsewhere. Lake Kivu in Rwanda, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence for outgassing events around the lake about every 1000 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 fortunately 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.
While Lake Kivu could be degassed in a manner similar to Lake Monoun and Lake Nyos, due to the size of the lake and the volume of gas involved such an operation would be expensive, running into millions of dollars. The about 500 million tons of carbon dioxide in the lake is a little under 2% of the amount released annually by human fossil fuel burning. Therefore the process of releasing it could potentially have costs beyond building and operating the system.
A scheme initiated in 2010 to utilize methane trapped in the lake as a fuel source to generate electricity in Rwanda has led to a degree of CO2 degassing.
During the procedure for extracting the flammable gas used to fire power stations on Kivu’s shore, some CO2 is removed in a process known as scrubbing. It remains unclear whether enough of the gas will be removed in this way to ensure the danger of a limnic eruption posed by Lake Kivu will be completely eliminated.
A study in September 2005 by George Kling and other researchers at the University of Michigan found that gas was not being removed from Lake Monoun quickly enough to ensure that the disaster never happens again. Kling recommended the lowering of the existing pipe and the addition of a new one in order to release more carbon dioxide.
Limnic Eruptions
A limnic eruption — also referred to as a lake overturn — is a rare type of natural disaster in which carbon dioxide suddenly erupts from deep lake water, suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising CO2 displaces water.
Lake Nyos before and after the eruption. Iron forced to the surface after the
eruption oxidized, turning the lake a brown rust color.
Scientists believe landslides, volcanic activity, or explosions can trigger such an eruption. Lakes in which such activity occurs may be known as limnically active lakes or exploding lakes. Some features of limnically active lakes include:
• CO2-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 CO2 saturations
• Proximity to areas with volcanic activity
It’s such a rare and bizarre phenomenon that to date there are only 2 recorded eruptions of this kind in history, at Lake Nyos and Lake Monoun.
Scientists have recently determined from investigations into the mass casualties in the 1980′s at Lake Monoun and Lake Nyos, that limnic eruptions and volcanic eruptions, although indirectly related, are actually separate types of disaster events.
Due to the nature of the event, it’s hard to determine if limnic eruptions have happened elsewhere. Sample sediments from the Lake Kivu were taken by Professor Robert Hecky from the University of Michigan which showed that an event caused living creatures in the lake to go extinct approximately every 1000 years, and caused nearby vegetation to be swept back into the lake.
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.
For a limnic eruption to occur, the lake must be nearly saturated with gas. In the 2 known cases, the major component was CO2, however, in Lake Kivu, scientists are concerned about the concentrations of methane gas as well. This CO2 may come from volcanic gas emitted from under the lake or from decomposition of organic material.
Before a lake is saturated, it behaves like an unopened can of soda pop — the CO2 is dissolved in the water. In both the lake and the soft drink, CO2 dissolves much more readily at higher pressure. This is why bubbles in a can of soda only form after the drink is open. The pressure is released and 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 at the bottom. This means that huge amounts of CO2 can be dissolved in large, deep lakes. Also, CO2 dissolves more readily in cooler water, such as that at the bottom of a lake. A small rise in water temperature can lead to the release of a large amount of CO2.
Once the lake is saturated with CO2, it becomes very unstable, and a trigger is all that’s needed to set off an eruption. In the case of the 1986 eruption at Lake Nyos, landslides were the suspected triggers, but an actual volcanic eruption, an earthquake, an explosion, or even wind and rain storms are other possible triggers.
The trigger pushes some of the saturated water higher in the lake, where the pressure is insufficient to keep the CO2 in solution. Bubbles start forming and the water is lifted even higher in the lake, where even more of the CO2 comes out of solution. This process forms a column of gas. At this point the water at the bottom of this column is pulled up by suction, and it too loses its CO2 in a runaway process. This eruption pours CO2 into the air and can also displace water to form a tsunami.
There are several reasons this type of eruption is very rare:
• First, there must be a source of the CO2, so only regions with volcanic activity are at risk.
• Second, temperate lakes such as North America’s Great Lakes, turn over each spring and fall as a result of seasonal air temperature changes, mixing water from the bottom and top of the lake, so CO2 that builds up at the bottom of the lake is brought to the top where the pressure is too low for it to stay in solution and it escapes into the atmosphere.
• Finally, a lake must be quite deep to have enough pressure to dissolve large volumes of CO2. So only in deep, stable, tropical, volcanic lakes such as Lake Nyos are limnic eruptions possible.
Once an eruption occurs, a large CO2 cloud forms above the lake and expands to the neighboring region. Because CO2 is denser than air, it has a tendency to sink to the ground while pushing breathable air up.
As a result, life forms that need to breathe oxygen suffocate once the CO2 cloud reaches them, as there is very little oxygen in the cloud. The CO2 can make human bodily fluids very acidic, potentially causing CO2 poisoning. As victims gasp for air they actually hurt themselves more by sucking in the CO2 gas.
Killer Lakes – National Geographic
