Introduction to Lake Nyos
Lake Nyos (; NEE-ohs ) is a crater lake in the Northwest Region of Cameroon, about 315 km or 196 miles northwest of the capital Yaoundé. It is a very deep lake found high on the flanks of a dormant volcano found in the volcanic plain of Oku along the line of volcanic activities in Cameroon. A volcanic wall dams the water of the lake.
Beneath the lake lies a pocket of magma, from which carbon dioxide (CO2) leaks into the water and changes it to carbonic acid. Nyos is only one of three lakes known to be saturated in this way and consequently prone to limnic eruptions, with the others being Lake Monoun, also located 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, the most notable one being Chah, which was abandoned after the incident. The limnic eruption did not only devastate human and livestock populations but also diversified aquatic lives like that of the tilapia, crabs, snails, and frogs, which was a significant loss in biodiversity both in and around the lake.
Although not a first, it was the largest known asphyxiation caused by a natural phenomenon. To avoid the repetition of the event, a degassing tube siphoning water from the bottom layers to the top, letting the carbon dioxide leak in a safe amount, was installed in 2001. Two more tubes were added in 2011.
Today, the lake also threatens with its natural wall weakening. The geological tremor may cause the natural levee to break off, and waters may rush through the downstream villages into Nigeria. A lot of carbon dioxide may be released.
Geography
Lake Nyos is situated within the Oku Volcanic Field, which is on the northern side of the Cameroon Volcanic Line, an area of volcanoes and other tectonic activity that extends southwest to the Mt. Cameroon stratovolcano. The field is characterized by volcanic maars and basaltic scoria cones.
Lake Nyos is a volcanic crater lake located in the Northwest region of Cameroon, in Central Africa. Specifically, it is situated in the Oku volcanic field, which is part of the larger Cameroon volcanic line—a chain of active and dormant volcanoes that stretches through Cameroon. The lake itself is positioned at an altitude of approximately 1,000 meters (3,280 feet) above sea level, nestled in a remote and mountainous area. The nearest major town to the lake is Bambili town, which is about 35 kilometers in the north-eastern part, although it still remains sparsely populated and relatively isolated.
The geographical coordinates of Lake Nyos are about 6.22°N latitude and 10.21°E longitude. The lake is situated within the larger volcanic landscape of the Western High Plateau, which is marked by rugged topography, steep slopes, and deep valleys. The surrounding landscape is lush and green, featuring tropical rainforest and savannahs, with the highland area having cooler temperatures compared to the lower coastal regions of Cameroon.
Lake Nyos is a maar lake, which means it was formed in a volcanic crater created by a volcanic eruption. The lake occupies the collapsed caldera of an ancient volcanic eruption, which is believed to have occurred several thousand years ago. Its size is relatively modest, covering an area of about 1.5 square kilometers (0.58 square miles) and reaching a maximum depth of around 208 meters (682 feet). The lake’s waters are unique due to their high concentration of dissolved gases, especially carbon dioxide, which have contributed to a number of extraordinary and dangerous phenomena.
One of the most notable features of Lake Nyos is its potential for hazardous gas release. The lake is stratified, with cooler, denser water at the bottom and warmer, less dense water at the surface. Under normal conditions, the deep waters of the lake store large amounts of carbon dioxide, a byproduct of volcanic activity in the region. This gas is typically trapped by the water’s layers due to the pressure and low mixing of water within the lake. However, if this pressure is disturbed—due to changes in temperature, seismic activity, or other factors—the gas can rapidly escape, potentially creating a deadly release.
This phenomenon was tragically highlighted in 1986 when a massive carbon dioxide eruption occurred, known as the “Lake Nyos disaster.” A sudden release of CO2 from the lake killed over 1,700 people and thousands of livestock in the surrounding villages, as the gas, heavier than air, flowed down into the valleys, displacing oxygen and asphyxiating those in its path. The disaster drew international attention to the dangers of volcanic lakes, especially those with large amounts of dissolved gas.
Despite its remote location, Lake Nyos continues to be closely monitored by scientists and authorities, given the ongoing risks it poses. Researchers have worked to develop methods for safely venting the gas from the lake to prevent another disaster. In recent years, techniques such as degassing projects have been implemented, where gas is slowly released from the lake in a controlled manner, reducing the risk of a sudden and catastrophic outburst. These efforts are part of ongoing research aimed at improving our understanding of volcanic lakes and their behavior.
The region surrounding Lake Nyos remains sparsely populated, with many people in the vicinity still practicing traditional subsistence agriculture, farming, and fishing. Despite the dangers, the area has a rich natural beauty, attracting some adventurous visitors and researchers interested in its volcanic and ecological aspects. The surrounding landscapes are home to a variety of plant and animal species, many of which are endemic to the region.
Lake Nyos is also culturally important to the local communities, especially to the ethnic groups who live in the surrounding areas. The groups usually view the lake with a combination of reverence and caution, since it is both beautiful and dangerous. Local legends and stories about the lake reflect the respect with which the people treat this powerful natural feature, acknowledging the threat it poses while also appreciating its place in the landscape.
In conclusion, Lake Nyos is not only a geographical marvel but also a natural reminder of the volatile forces at work beneath the Earth’s surface. Its location in the Oku volcanic field, its geological features, and its potential for catastrophic gas emissions make it both a subject of scientific study and a reminder of the power of nature. The lessons learned from past disasters continue to shape efforts to monitor and protect the people living near the lake, and the ongoing research into volcanic lakes may help prevent similar tragedies in the future.
Formation and geologic history
Lake Nyos lies south of the dirt road from Wum, roughly 30 km (19 mi) to the west, to Nkambé in the east. Villages along the road in the general area of the lake include Cha, Nyos, Munji, Djingbe, and Subum. It lies 50 km (31 mi) from the Nigerian border to the north, and is on the northern slopes of the Massif du Mbam, drained by streams running north, then northwest, to the Katsina-Ala River in Nigeria, which is part of the Benue River basin.
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 a maximum of 12,000 years ago, and is 1,800 m (5,900 ft) across and 208 m (682 ft) deep.
This 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, though 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 80 kilometers (50 mi) directly below the lake resides a pool of magma, which releases carbon dioxide and other gases; the gases then travel upward through the earth. The fumes dissolve in the natural springs encircling the lake, ultimately rising to the surface of the water and leaching into the lake. However, with advancements in technology, machinery has now been placed at the bottom of the lake to remove the gases, ensuring the safety of the inhabitants in the area.
The lake waters are retained by a natural dam formed by volcanic rock. The wall stands 40 meters (130 ft) high and 45 meters (148 ft) wide at its narrowest point.
Gas saturation
One of only three carbon dioxide-saturated lakes in the world, the others being Lake Monoun in Cameroon and Lake Kivu, which lies between the Democratic Republic of the Congo and Rwanda, Lake Nyos is fed by a large magma chamber located below the region, which seeps up through the lake bed to charge the waters of Lake Nyos with an estimated 90 million tonnes of CO2.
Lake Nyos is thermally stratified, with layers of warm, less dense water near the surface floating on the colder, denser water layers near the lake’s bottom. Over long periods, carbon dioxide gas seeping into the cold water at the lake’s bottom is dissolved in great amounts.
Most of the time, the lake is stable and the CO2 remains in solution in the lower layers. However, over time, the water becomes supersaturated, and if an event such as an earthquake or landslide occurs, large amounts of CO2 may suddenly come out of solution.
1986 disaster
Although a sudden outgassing of CO2 had occurred at Lake Monoun in 1984, a similar threat from Lake Nyos was not anticipated. However, on August 21, 1986, a limnic eruption occurred at Lake Nyos, triggering the sudden release of about 100,000–300,000 tons (some sources state as much as 1.6 million tonnes) of CO2.
This gas cloud rose at nearly 100 kilometers per hour (62 mph) and spilled over the northern lip of the lake into a valley running roughly east–west from Cha to Subum. It then rushed down two valleys branching off to the north, displacing all of the air and suffocating 1,746 people within 25 kilometers (16 mi) of the lake, mostly rural villagers, as well as 3,500 livestock. The villages most affected were Cha, Nyos, and Subum.
From evidence, scientists concluded that at the surface of the lake, a fountain of water and foam, 100 m (330 ft), formed. The massive volume of water that rose suddenly caused much turmoil in the water, which spawned a wave of at least 25 meters (82 ft) that would scour the shore of one side.
It is unknown what caused the massive outgassing. Many geologists suspect it was a landslide, but some think a minor volcanic eruption happened on the bottom of the lake. A third idea is that rainwater hitting the lake on one side cooled down, causing the overturn. Others believe the earthquake was actually minor, while in any case, because nothing had been seen shaking the town that morning during the disaster, the idea appears improbable.
As the matter went, however much of a rumpus might have caused whatever happened, that mixed the highly saturated water in the deeper levels of the lake with its upper layers immediately where reduced pressure provided enough room in solution for dissolved CO2 to effervesce out of.
It is estimated that approximately 1.2 cubic kilometers (0.29 cu mi) of gas was emitted. The usually blue-colored waters of the lake turned deep red after outgassing was lost because the iron-rich water from the deep came up to the surface and oxidized through the action of air. It is said that the level of the lake went down by about a metre and trees close to the lake were uprooted.
Degassing
The 1986 disaster scale called for much study on how to prevent a recurrence. Estimates of the rate of carbon dioxide entering the lake suggested that outgassings could occur every 10–30 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.
Several researchers independently proposed the installation of degassing columns from rafts in the lake. These use a pump to initially lift water from the bottom of the lake, heavily saturated with CO2, until the loss of pressure begins releasing the gas from the diphasic fluid, at which point the process becomes self-powered. In 1992 at Monoun, and in 1995 at Nyos, a French team directed by Michel Halbwachs demonstrated the feasibility of this approach. In 2001, the U.S. Office of Foreign Disaster Assistance funded a permanent installation at Nyos.
In 2011, two additional pipes were installed by Michel Halbwachs and his French-Cameroonian team to assure the complete degassing of Lake Nyos.
After the tragedy, scientists researched other African lakes to determine whether something similar could occur there as well. Lake Kivu, which is 2,000 times bigger than Lake Nyos, was also found to be supersaturated, and geologists discovered that there were evidence for outgassing events about every thousand years around the lake.
In 2002, the eruption of nearby Mount Nyiragongo sent lava flowing into the lake, and fears that a gas eruption could be triggered proved unfounded because 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.
Weakening dam
In 2005, 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 the dam’s strength on the outside. Seismic activity caused by the lake’s volcanic foundation could thus cause the lake wall to give way, resulting in up to 50 million m³ (1.8 billion ft³) of water flooding downhill into areas of the Northwest Province and the Nigerian states of Taraba and Benue.
The Cameroonian government, speaking through Institute of Mining and Geological Research Gregory Tanyi-Leke, acknowledges the weakened wall, but denies that this poses any current 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 three days in September 2005 and confirmed the natural lip had indeed weakened. Van Duin believed that the dam would breach within the next 10 to 20 years.
One way the disaster could perhaps be prevented from happening is strengthening the lake wall, which of course would take plenty of time and money. In addition, the engineers could devise a channel, allowing excess water to drain into it; this would significantly reduce pressure on the wall if the level of water lowered by about 20 m or 66 ft.
1. What Caused the Deadly Gas Release at Lake Nyos in 1986?
In 1986, Lake Nyos in Cameroon became infamous for a catastrophic event that led to the deaths of nearly 1,800 people. The cause was a sudden release of carbon dioxide (CO2), which had been trapped at the bottom of the lake for centuries. The gas, which is heavier than air, was released in a massive eruption, suffocating anyone in the vicinity. While this event has been studied extensively, the precise trigger for the release remains one of the most debated aspects of the disaster.
Scientists believe that a combination of factors, such as volcanic activity beneath the lake and temperature fluctuations, may have caused the lake’s deep waters to destabilize. This would have caused the CO2 to be released rapidly in a phenomenon called a limnic eruption. However, the specific triggers for this sudden release are still not completely understood.
Experts have speculated that an earthquake or a landslide may have disturbed the lake’s stratified layers, which led to the sudden mixing of the gas-rich lower waters with the surface. Others think that seasonal changes in temperature and wind might have contributed to the event. Though research into the causes of the 1986 disaster continues, it remains unclear exactly why the eruption occurred when it did.
In the years following the disaster, scientists and environmentalists have worked to better understand the dynamics of Lake Nyos and prevent similar events from occurring in the future. One solution has been to install degassing pipes in the lake, which allow controlled release of the CO2 gas to prevent another potentially fatal eruption. This action has made the area safer, but the mystery of what specifically caused the 1986 event still remains.
2. Why Are the Gas Bubbles Trapped Under the Lake?
Lake Nyos sits in a volcanic crater, which makes it a highly unusual and dangerous body of water. The lake’s composition is unique because of its high levels of dissolved carbon dioxide, which originates from volcanic activity beneath the lake. This CO2 gas is continually produced by the volcanic activity in the area and is slowly absorbed into the water.
One of the greatest mysteries surrounding Lake Nyos is how the gas bubbles become trapped in the deep waters. The lake is characterized by its stratification, with the surface water being much less dense than the deeper layers. Because the CO2 gas is heavier than water, it remains in the bottom layers of the lake, which is under high pressure. This stratification helps to trap the gas, but the exact process by which the gas stays suspended is still a subject of intense research.
What makes the situation even more mysterious is that the lake has remained relatively stable for centuries, despite the constant input of CO2 gas. Scientists are still trying to understand how the lake manages to keep the gas from escaping until something disturbs the delicate balance. Some researchers hypothesize that the lake’s volcanic nature and particular depth help to maintain this gas storage system, but the true mechanism behind it is not entirely understood.
The most terrifying aspect of the trapped CO2 is that, if disturbed, it can be released in a catastrophic event. The 1986 gas eruption demonstrated just how dangerous it can be when the lake’s natural “cork” is disturbed. Despite efforts to manage the risk with degassing techniques, understanding the long-term behavior of these gas bubbles is still a major mystery that scientists continue to investigate.
3. What Role Does Volcanic Activity Play in Lake Nyos’ Uniqueness?
Volcanic activity is central to understanding the mysteries of Lake Nyos. The lake is situated in a volcanic crater, and beneath it lies an active volcanic system that produces significant amounts of carbon dioxide (CO2). This gas is absorbed into the lake’s water, particularly in the deeper regions, due to the high pressure at the bottom. Over time, the volcanic activity has created a unique situation in which gas builds up in the lake, often without noticeable changes at the surface.
The volcanic processes that feed Lake Nyos’ CO2 supply have been active for thousands of years. However, the precise relationship between the volcanic activity and the gas buildup is still not fully understood. One theory is that the magma below the lake is slowly releasing CO2 over time, which dissolves into the water. The lake itself sits on a tectonic fault line, adding another layer of complexity to the volcanic activity in the region.
Volcanic eruptions, either nearby or beneath the lake itself, could potentially stir the lake’s deep waters, leading to the release of the trapped gas. However, no eruptions have been observed at Lake Nyos in modern history, and yet the gas buildup continues. Some scientists believe that subtle volcanic events could be occurring beneath the lake that have not yet been detected, suggesting that there might be hidden volcanic forces at work beneath the surface.
Furthermore, researchers have considered the possibility that the CO2 accumulation may be influenced by shifts in tectonic plates in the region, though this remains an open question. The complexity of the interaction between volcanic activity and the lake’s gas dynamics is one of the key factors contributing to the ongoing mystery of Lake Nyos.
4. Could an Earthquake Have Triggered the 1986 Gas Release?
The 1986 disaster at Lake Nyos was a significant event in geological studies, with many questions about what caused the deadly release of gas. One of the most widely discussed theories is that an earthquake might have triggered the release of carbon dioxide from the lake. Earthquakes are known to cause disturbances in the earth’s crust, and given Lake Nyos’ location along a tectonic fault line, seismic activity is always a possibility.
While no major earthquake was recorded at the exact moment of the gas release, there was a noticeable tremor in the region around the time of the event. Some researchers suggest that this tremor could have been enough to disturb the delicate layers of gas and water, causing a sudden mixing of the CO2-rich deep waters with the surface. If this disturbance was enough to cause a shift in the water column, it would have led to the explosive release of gas that overwhelmed the surrounding areas.
The timing of the tremor, which occurred just before the gas eruption, has led many scientists to consider this as a potential cause of the event. However, there has been no direct evidence proving that the earthquake alone could have caused such a large-scale release. Still, it is a possibility that cannot be ruled out entirely, and ongoing research into seismic activity in the region may provide more answers.
The earthquake theory also raises important questions about how the lake’s gas storage system behaves under pressure. Could a minor seismic disturbance be enough to trigger such a catastrophic event? This is something scientists continue to investigate, as it would have implications for the safety of the surrounding communities.
5. Why Did Only the People Near the Lake Suffer the Effects of the Gas Release?
The 1986 gas eruption at Lake Nyos claimed the lives of nearly 1,800 people who were living in the nearby villages. One of the most intriguing aspects of the event was that the CO2 gas released from the lake seemed to have a limited effect, mostly suffocating those closest to the lake. People who lived farther away were largely unaffected, even though the gas cloud spread for miles.
The gas that was released from the lake was heavier than air, which meant it stayed close to the ground, accumulating in the valleys and low-lying areas surrounding the lake. Because of this, the villages nearest to the lake, which were situated in these low-lying areas, were the hardest hit. The CO2 cloud enveloped the region, suffocating anyone who was within its reach.
The geography of the area played a significant role in the effects of the gas release. The gas spread more quickly in the valleys because the dense CO2 pooled in these depressions. Higher regions, which were not as susceptible to the gas cloud, saw fewer fatalities. This explains why the people in the surrounding villages near the lake experienced the brunt of the disaster, while those living at higher altitudes were largely safe.
The phenomenon of the gas being concentrated in specific geographic areas remains a key mystery. Scientists continue to study how the landscape, weather patterns, and topography influenced the behavior of the gas and why the effects were so localized.
6. How Did the Ecosystem of Lake Nyos Recover After the Gas Eruption?
After the catastrophic event of 1986, the surrounding ecosystem of Lake Nyos was severely affected. The release of large amounts of CO2 into the atmosphere not only claimed human lives but also caused massive damage to the local fauna and flora. The dense cloud of CO2 displaced oxygen, suffocating both plant and animal life in the vicinity of the lake.
In the aftermath, researchers observed a sharp decline in the aquatic life within the lake. Fish and other organisms were found dead or severely harmed due to the sudden depletion of oxygen in the water. Similarly, the nearby forest and wildlife were affected, as many animals were either killed by the gas or forced to flee the area. The death of so many organisms raised questions about how the ecosystem could recover after such an event.
However, over time, the ecosystem around Lake Nyos began to show signs of recovery. The introduction of degassing techniques, which slowly release CO2 from the lake in a controlled manner, helped to stabilize the water conditions and promote the return of life. Scientists also noted that some species of fish and other organisms began to repopulate the lake in the years following the eruption.
The recovery of the ecosystem has been a slow but ongoing process. The lake’s unique conditions, with high levels of dissolved CO2, make it difficult for typical aquatic life to thrive. Nevertheless, over time, the region has seen a gradual resurgence of both plant and animal species. Still, the full recovery of the ecosystem is uncertain, as there is ongoing research into how these extreme conditions affect long-term biodiversity.
7. How Does Lake Nyos’ CO2 Degassing System Work?
After the 1986 gas eruption at Lake Nyos, scientists and engineers devised a degassing system to prevent a similar catastrophe from happening again. The system works by slowly releasing the CO2 that has been trapped in the deep waters of the lake, reducing the risk of another explosive eruption.
The degassing system consists of large pipes that are anchored to the lakebed. These pipes are designed to reach the deepest parts of the lake where the CO2 is most concentrated. Once the system is activated, gas bubbles are gradually released to the surface through the pipes, where they are safely vented into the atmosphere.
The technology was implemented in the years following the 1986 disaster as a precautionary measure. The hope is that by regularly releasing the gas in a controlled manner, the pressure in the lake will be reduced, and the risk of a sudden and catastrophic gas eruption will be minimized.
While the degassing system has been successful in reducing the risks of CO2 buildup, some questions remain about its long-term effectiveness. Will it be enough to prevent another event? Could the system fail under certain conditions? These are still unanswered questions that researchers are working to resolve.
8. Why Is Lake Nyos’ CO2 Concentration So High?
One of the most striking features of Lake Nyos is its exceptionally high concentration of dissolved carbon dioxide. The lake’s volcanic activity produces CO2, which dissolves into the water, particularly in the deeper, colder layers. Unlike most other bodies of water, Lake Nyos has accumulated a large volume of CO2, making it highly unstable.
The high CO2 concentration can be attributed to the lake’s position in a volcanic crater, where the volcanic activity below continually releases gas into the water. Additionally, the lake’s depth and the fact that it is a closed basin, meaning it has limited water exchange with other bodies of water, contribute to the accumulation of gas over time.
While scientists understand the basic processes that contribute to the high CO2 concentration, they still don’t fully understand why the lake has such an extraordinary buildup of gas. There are several theories, but none of them have been conclusively proven. Some researchers suggest that the particular geological conditions of the area may play a significant role, while others point to the unique combination of factors that make Lake Nyos different from other lakes.
This unusually high concentration of CO2 is both a scientific mystery and a serious environmental concern. Understanding how the lake’s CO2 is produced and retained is crucial for mitigating the risks of future eruptions.
9. Could Climate Change Influence the Behavior of Lake Nyos?
As with many natural phenomena, the potential impact of climate change on Lake Nyos has become a topic of increasing interest. The lake’s stability is influenced by a number of environmental factors, including temperature, atmospheric pressure, and precipitation patterns. Climate change could affect these factors and potentially influence the behavior of the lake’s gas buildup.
Warmer temperatures, for example, could lead to more frequent or intense mixing of the lake’s layers, which could disturb the trapped CO2 and cause a sudden release. Additionally, changes in precipitation patterns could alter the lake’s water levels and contribute to changes in the way gas is dissolved into the water.
While the full impact of climate change on Lake Nyos is still uncertain, it’s possible that rising global temperatures could make the situation more unpredictable. Researchers are closely monitoring the lake’s behavior in relation to these environmental changes to determine how vulnerable it might be to future events.
The question of how climate change will influence the behavior of such an extraordinary natural phenomenon remains an open one, and scientists continue to study the lake’s interactions with its environment to understand the full scope of the issue.
10. Why Are People Still Living Near Lake Nyos Despite the Risks?
Despite the catastrophic events of 1986, people continue to live in the vicinity of Lake Nyos, and the area is still populated today. One reason for this is the reliance of the local population on the natural resources surrounding the lake. Many villagers depend on farming and fishing in the area, which has led them to remain despite the known risks.
Another factor is the absence of immediate signs of danger. Since the installation of the degassing system and the relative stability of the lake in recent years, many people believe the risk of another catastrophic eruption has been mitigated. However, this perception may be misleading, as there are still many unknowns about the lake’s behavior.
Researchers have raised concerns about the potential long-term risks associated with living near Lake Nyos. While the degassing system has reduced the immediate threat, it does not eliminate the possibility of another eruption. Local governments and environmental agencies have taken steps to educate the population about the risks, but many people continue to live near the lake, either due to necessity or a lack of alternative options.
The decision to live near the lake is complicated by both practical and cultural factors, as the residents have deep connections to the land. Understanding why people continue to live in this dangerous area and finding ways to support them while ensuring their safety is another mystery surrounding Lake Nyos.
