Lake Nyos, Cameroon, August 1986

If you’ve never been to a crater lake – you really should go see one. They sit in deep geologic cups formed by an extinct volcanic crater. As you climb the outer rim,  the lake itself is often hidden from sight. The experience of hiking over the rim of the crater and suddenly looking down on an expanse of beautiful green trees and plants thriving in the lava soil surrounding the water jewel in the center is other-worldly. The water is a color that you only find in your imagination – the deepest blues, emeralds, and jades. As you descend steeply to the water’s edge, the lush trees and plant life give way to reveal a body of water the color of sapphire or jade. The part of you that is still connected to ancient feelings knows that you are in a strange and magical place.

Crater Lake, Oregon

Geologically, crater lakes form after a volcano has finished erupting, and the central area collapses into a chalice-shaped cone or caldera. Crater lakes are not filled with water from rivers or streams. Water seeps in from the surrounding rock and the caldera collects rainwater over many years. Debris settles, minerals concentrate, and the water clarifies to a crystalline brightness.  

There are about 300 crater or volcanic lakes throughout the world. In the US, they are mostly located in the northwest. Oregon has the most famous one aptly named Crater Lake. Klamath Indians thought Crater Lake a site too sacred to even gaze upon without risking death and lasting sorrow. If you went there now, for example, you might still see the “Old Man” of the lake. Once a 35-foot tall mountain hemlock, it’s been floating in the water for well over 100 years. No big deal, until you discover that it is floating vertically as if it was planted in the water! It has slowly sunk, but to this day, about 3 feet of it sticks straight up in the air as it slowly bobs around the lake. Park Rangers used to row out to it, climb on it, and get their picture taken. Not any more. Sudden misfortune and horrible weather seem to follow those who taunt the Old Man of the lake. 

To further explore the crater lakes, head to Cameroon, in West Africa. The Bantu tribes occupy the highlands around those lakes where they have prospered with agriculture, trade, and ironwork. They know that these lakes are infused with evil spirits that command fear and respect, the most notable spirit being Mami Wata. They tell stories of the lakes disappearing at midday to reveal the homes of the dead, only to reappear if the person would shout. The flat reflective surface of these lakes plays tricks on the eye and stirs the soul. The reflected sky on the mirror-like surface seems as real in the water as it does in the air above it. Mami Wata is always depicted in West African culture as a beautiful and alluring woman with a snake wrapped around her torso. She can take the form of a mermaid or a human, and it is said she attracts young men to come into the water, often to their death. Mami Wata can take a full human figure as well and will wander around on market day looking for her next victim. Members of the Fulani tribes who live in the villages below Lake Nyos are a little less inclined to believe such stories. They are Muslim cattle herders who began to move into this mountainous region in Cameroon from the north roughly a century ago.  They pay no mind to the dangers of Mami Wata.

To really understand the terrible power and mystery of crater lakes, you have to travel back in time to a typical market day in the rainy season, on August 21, 1986, in Lower Nyos village in Cameroon. Wander through the market and go from stall to stall. You’ll see villagers under small grass canopies selling cassette tapes, rugs, steel pans, palm oil, grains, and spices. The skies will occasionally interrupt the routine with a cloudburst. You would see for yourself what everyone will later remember.  This was the kind of routine day that everyone will recall as beautiful, only perhaps because it ended in such a horrifying way.

Lake Nyos is about 3500 feet above sea level in Cameroon near the border of Nigeria. Lower Nyos village lies in the valley below Lake Nyos, while Upper Nyos village peeks out over the lake. Lower Nyos village, like neighbors Cha, Subum, and Fang, are situated along the river Mbum. In the rainy season, when Lake Nyos overflows its small spillway, water runs down the granite hills into the Mbum and the valleys below. The Fulani herders who live in these valleys do not think much about Mami Wata and her wicked ways. They enjoyed raising their cattle on the fertile lands in these valleys. Like any typical market day in the wet season, after the chores were done, the cattle looked after, and the children tucked in the villagers headed to bed. 

Lake Nyos, Cameroon

Joseph Nkwain lived by himself in Subum, below Lake Nyos, in the Mbum river valley. His daughter was staying with him on holiday from school. Joseph remembers being jolted awake at 11:30 PM on the night of August 21, 1986, by a loud airplane noise. Thinking he was dreaming, he was at first bewildered. His skin was hot, and he was surrounded by overpowering smell – dry, acrid, and like gunpowder. He heard his daughter snoring, not from a deep sleep, but rather breathing in a frighteningly unusual way. He got up to check on her and collapsed. He lay on the ground for nine more hours until the next morning when he was awakened by a neighbor, also recovering, banging on his door. As he got up from the ground, Joseph noticed he was covered in honey-colored stains with a starchy residue. He had circular burn wounds or abrasions on his body. Unable to speak, he crawled to his daughter’s bed. She would not respond. He collapsed again. Finally, at 4:30 PM, he was able to stand and take full stock of his situation. His daughter lay motionless in her bed, now dead. He stumbled weakly out of his house and walked to his neighbor’s house. Upon entering, he found them all to be lifeless as well. Some were lying in doorways as if they had tried to flee and collapsed after a few steps. Others in their beds as if they simply never woke up. Cattle were dead in the fields. Chickens were killed in their coops. Strangely, even vultures, flies, and small ants were dead. 

Joseph went back and found his only living neighbor lying in his bed, too weak to stand up.  Leaving him, Joseph got on his motorcycle and rode through the village of Nyos to the neighboring village of Cha. There were no survivors, only dead bodies, dead cattle, dead chickens, death everywhere. As he got further away from Nyos, he would occasionally encounter a few survivors like himself.  They were wandering around confused and feeling ill and coughing with burns on their bodies, headaches, and muscle pains. The few chicken or cattle that survived staggered around no better off. Joseph slowly made his way on his motorcycle to his workplace at the Wum Area Development Center, some 36 miles away. His boss, hearing his incredible story and seeing him so ill, took him from Wum to the hospital. 

Slowly, survivors began to make their way to the hospital over the next day or so. They would all tell the same mysterious story. One minute lying in bed, the next minute awakened dazed and confused with skin burns, walking among the dead. Only the villagers who lived in the highest elevations in Upper Nyos village were able to give an accurate description of events. There, with a clear view of Lake Nyos from their vantage point a few hundred feet above the surface, they described how they watched the lake transform into maleficence. Late in the evening before sunset, the Lake started to make popping and hissing sounds and jets of water shot up from the surface. From this, a ghostly plume of vapor emerged. The water level in the lake rose, and it turned muddy red. The popping and hissing were so loud that villagers a few miles away who could not see the lake assumed that an inter-tribal gunfight was underway. Over 3 hours, the lake labored and expelled and a monstrous 150-foot cloud of hot, wet vapor. Once airborne, the mist snaked down the mountainside, following the valley floors to the villages below. Death was determined by whether you were covered by the vapor cloud or not. Wherever it covered the earth, it snuffed out all living things. It extinguished kerosene lamps. It was silent, deliberate, and instantly deadly.

Hadari, a Fulani cattle herder, saw it for himself. He lived on a hillside above the lake. The rumbling noise awoke him as well, and he rushed out to see the ghostly plume of vapor emerge. The stench gagged him. He rushed back to his home and hurriedly took his family to higher ground and hid in the bush. Even when the noise finally stopped, they were too frightened to return to their home and waited until the next morning to make their way back to their home. There they saw what everyone else did – evidence of instant death. Bodies in doorways and bodies on beds in positions suggesting instant death, sometimes lying one on top of the other.  

Cattle found dead near Lake Nyos, August 22, 1986

Word of the disaster soon spread as the survivors made their way to distant clinics and hospitals. The death toll reached 1700 people and similar numbers of livestock. Teams from area agencies mobilized and arrived in the area days to weeks later bring aid, but it was too late. Lake Nyos lay silent. It only remained to begin burying the dead and assist the 4,000 refugees whose homes, cattle, and families had been decimated. 

Lake Nyos post-event

Aid workers asked what happened? How could a lake seemingly start to boil? What was the gas cloud that emerged from the lake? Why was it so deadly? Would the lake boil again? Emit another deadly monster? The Bantu’s knew the answers. They recognize the capricious hand of Mami Wata. They knew not to trust Mami Wata, not to be enchanted by her evil beauty and live below the lake within the grasp of her deadly spirt. No, it was only the scientists that came in weeks to months later who could not agree on what happened. 

After word of the disaster spread, a sense of urgency arose in the scientific community to find an explanation and prevent the next catastrophe. Volcanologists from research labs around the world, such as the University of Savoie Mont Blanc in the French Alps, arrived on the scene and began to investigate. Although Lake Nyos seemed quiet, a simple experiment revealed much. Investigators rowed out to the center of the lake and took a sample of water deep below the now seemingly calm surface. The water, once brought up to the surface and opened, began to bubble and fizz like a bottle of soda. There was dissolved gas in the lake! Testing revealed that the gas was carbon dioxide (CO2) – the same gas in carbonated soda or water. Perhaps the volcano that formed Lake Nyos was not so dormant after all. Did a massive gas eruption originate from the remnants of the volcano, broil up through the lake and into the atmosphere? Or was it slowly infusing the lake with CO2 saturated water, and creating a soda can waiting to explode? Maybe it was neither of those?  Maybe CO2 had gradually built up from decomposing organic material deep in the crater. The heavy rain on market day might have caused a mudslide into the lake sufficient to shake the soda can, cause the lake to release its gasses, and overflow the crater. 

Meanwhile, scientific experts and locals began to connect some fascinatingly similar dots. Locals recalled an event, two years earlier, at nearby Lake Monoun that killed 37 in a nearby village. Although unnoticed internationally when it happened, it now fit the same pattern as Nyos. Perhaps it was the entire chain of crater lakes that was a threat to explode! This would confirm the concept that a steady supply of water saturated with CO2 was continually dissolving into the lakes and, in fact, the lakes would explode again. But when? Scientists began by measuring the amount of dissolved CO2 remaining in the lake. Their results concerned them greatly. It would only take 10 more years for Nyos to be sufficiently saturated with gas to explode once again.

Carbon dioxide gas explains the sudden deadly nature of the vapor cloud. Carbon dioxide is an odorless colorless gas that is exhaled from our bodies as a waste product of respiration. Plants, conversely, absorb carbon dioxide. Carbon dioxide is a greenhouse gas produced naturally in every exhaled breath of animals, by the decomposition of organic material, and burning carbon-based fuels. Dry ice is the solid form of carbon dioxide. Throw a piece in a bucket of water, and a ghostly mist will boil out. What you are witnessing is a carbon dioxide gas from the dry ice warming up. That mist is probably very close to the cloud that emerged from Lake Nyos. That mist perhaps also dragged some sulfur-containing compounds such as methane gas along with it – giving it the odor of rotten eggs, matches, or gunpowder.

There is a good reason we exhale carbon dioxide from our bodies. It is the by-product of our oxygen-based metabolism and is poisonous to all living things. At first, your body responds by increasing the rate of respiration to exhale it – but of course, this only causes a higher amount of carbon dioxide to be inhaled. Then as the acidity of your blood worsens, cellular functions cease. The rising levels in the brain have a narcotic effect, depressing brain function, and slowing respiration. This is the death spiral, as slowing respirations prohibit exhalation of the CO2 gas. As a result, the acid level rises, and finally, the heart and lungs cease to function. Victims might sleep through the experience on their way to death or awaken enough to get up and staggered a few steps before collapsing. The CO2 cloud would also displace any oxygen in the air, thus extinguishing kerosene lamps, candles, and the like.   

In the end, scientists agreed that CO2 was dissolving into the lake over time, that the lake had a capacity to absorb lethal amounts of this gas, and that it was only a matter of time before Nyos or another crater lake would explode again with lethal effects. A simple, low cost, workable solution was needed. Finally, in 1992 at Lake Monoun, a team of engineers from the French Ministry of the Environment demonstrated the feasibility of an elegantly simple solution to removing the gas from the lake – a drinking straw. 

Make no mistake, this was no ordinary drinking straw. First, it was made of polyethylene pipe, so that it was light enough to be placed deep in the lake by hand. Second, once assembled, it was 230 feet long. It was inserted into the lake one section at a time, each piece connected to the next working from a floating platform. With a bit of priming from a pump at the top of the pipe, the laws of physics are set into motion. As water is drawn to the surface, dissolved gas is eliminated, thus making the water lighter. Lighter water floats to the top of denser water, thus creating a sucking force to draw more water up the column on its own. Water is then pulled into the pipe from top to the bottom as a result of the suction and voila! The spontaneous eruption of a 70-foot geyser of carbonated water shot into the air over the lake. Once the details were worked out, it was clear that a handful of these types of straws in the lake could remove enough of the gas so that the lake would not erupt again. 

Six years later, a fully operational degassing pipe was installed at Lake Nyos. The urgency of the project was clearly evident when the new geyser went 164 feet into the air – 110 feet higher than the first test pipe six years prior. Similar pipes were installed at nearby Lake Monoun and at Lake Kivu in Rwanda. Furthermore, enthusiasm for this particular solution grew when it was discovered that Lake Kivu not only was full of carbon dioxide, it also had a massive store of dissolved methane gas. If safely extracted, this could provide a source of fuel and a new industry for the nation of Cameroon.  

Degassing Lake Nyos with CO2 vent

But taming Mami Wata is never so easy. The degassing of these large lakes is adding tons of CO2 into the atmosphere. Furthermore, the water that is coming to the surface has a low amount of oxygen and a high amount of iron hydroxide, which could prove deadly to the fish in the lake. Now that it is continuously being stirred, Lake Nyos has the reddish color of this iron hydroxide. So the process of taming the natural world, while at the same time preserving its inherent balance – however episodically violent – goes on. 


Think you are safe from such exotic disasters as exploding West African crater lakes? You might think again. Sitting in a large depression in eastern California, Mammoth Mountain is a young volcano on the southwest rim of Long Valley Caldera. The area is known for its skiing, hiking, and camping and draws about a million visitors a year. The last eruption of this volcano was about 200 years ago, but earthquakes are relatively frequent. In 1989, geologists reported a series of small earthquakes in the vicinity of nearby Horseshoe Lake, which caused no apparent damage. Months later, 100 acres of dead and dying trees in the region caught the eye of the US Forest Service. The killer – exceptionally high concentrations of CO2 in the soil. Since then, the death zone continues to expand. It even took the life of a healthy 58-year-old cross country skier from Torrance CA, who was found dead face down in the snow, the victim of CO2 poisoning.


Remember, it’s a dangerous planet – we only survive it. 


S.J.Freeth The anecdotal evidence, did it help or hinder investigation of the Lake Nyos gas disaster?

F. LeGuern, E. Shanklin, and S. Tenor Witness accounts of the catastrophic event of August 1986 at Lake Nyos (Cameroon)
E. Shanklin Exploding lakes and maleficent water in Grassfields legends and myth

P Baxter, M. Kupilia Acute health impact of the gas release at Lake Nyos, Cameroon, 1986




rjhamiltonmd View All →

Professor and Chair of Emergency Medicine at Drexel University College of Medicine and a Medical Toxicologist
Views are my own created for the purposes of furthering medical education using #FOAMED

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