Everything Everywhere Daily: History, Science, Geography & More - Limnic Eruptions: The Rarest Natural Disaster

Episode Date: January 10, 2023

Early in the morning of August 21, 1986, in a valley near Lake Nyos, Cameroon, something horrible happened.  1,746 people were killed, as were over 3,500 cattle and almost every other animal that breathed air.  There were no signs of violence or destruction. Everyone and everything seemed to have simply died.   They were the victims of one of Earth's rarest and most frightening disasters.  Learn more about limnic eruptions, what they are, and how they can be prevented on this episode of Everything Everywhere Daily. Subscribe to the podcast!  https://link.chtbl.com/EverythingEverywhere?sid=ShowNotes -------------------------------- Executive Producer: Charles Daniel Associate Producers: Peter Bennett & Thor Thomsen   Become a supporter on Patreon: https://www.patreon.com/everythingeverywhere Update your podcast app at newpodcastapps.com Discord Server: https://discord.gg/UkRUJFh Instagram: https://www.instagram.com/everythingeverywhere/ Facebook Page: https://www.facebook.com/EverythingEverywhere Facebook Group: https://www.facebook.com/groups/everythingeverywheredaily Twitter: https://twitter.com/everywheretrip Website: https://everything-everywhere.com/everything-everywhere-daily-podcast/ Learn more about your ad choices. Visit megaphone.fm/adchoices

Early in the morning of August 21st, 1986, in a valley near Lake Neos Cameroon, something horrible happened. 1,746 people were killed, as were over 3,500 cattle and almost every other living creature that breathed there. There were no signs of violence or destruction. Everyone and everything seemed to have simply died. They were victims of one of the Earth's rarest and most frightening disasters. Learn more about limnic eruptions, what they are, and how they can be prevented on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time

to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. Every natural disaster you can think of all has one thing in common. You know when it's happening. You cannot miss the high winds of a hurricane or the surging waters of a tsunami or the shaking ground of an earthquake or the explosions and pyroclastic flows of a volcano.

While all of those disasters are horrible, at least you know what's happening to you. What makes a limnic eruption so horrifying is you cannot see, hear, or feel what is happening. So what is a limnic eruption? as the name would suggest it has to do with lakes. Limnic eructions are extremely rare, and only a few have ever been recorded in human history. The earliest known case of a limnic eruption was documented by the Roman historian Plutarch. He noted that in the year 406 BC, the waters of Lake Albano, outside of Rome, surged over its banks and across the surrounding hills. The problem is that Lake Albano isn't a volcanic crater.

There's no tributaries that flow into the lake, and there was no rainfall. There was nothing that would cause the lake to flood. The water in the lake just spontaneously rose up and spilled out of the rim of the crater, destroying farm fields and vineyards. Plutarch wrote about this disaster almost 500 years after it occurred, so he wasn't a witness to the event, nor was he able to speak to eyewitnesses. It was something that was passed along for generations. It was a rather odd story to have survived for 500 years,

a lake just spontaneously rises up and spills over its banks. Fast forward almost 2,000 years from Plutarch. This time, instead of Italy, the place is the African country of Cameroon. The lake in question is Lake Monoon, located in the Oku volcanic field and also situated in a volcanic crater. On August 14, 1984, at 10.30 p.m., something happened at Lake Monoon. A gas cloud reportedly arose over the lake, sometime between 2.30 in the morning and dawn on the 15. 37 people on the eastern side of the lake were killed. The victims were found with slight skin damage,

and all of the plants around the village on the shore of the lake were found to have been crushed as if it was hit by a large wave. The deaths were a total mystery, and things just didn't add up. Some victims were found in a truck. The truck had stopped working, and two of the people in the truck got out and were killed. Two people sitting on top of the truck somehow survived. The working theory for the deaths of Lake Manoon was terrorism.

There had been some fighting in civil strife in Cameroon in the past, so the explanation was plausible, and quite frankly, nothing else made sense, other than somebody was testing a biological weapon in the area. There was no means or motive, but what else could it be? Well, just two years later, something similar and much more devastating happened. And again, this took place in Cameroon. This time, the event took place in Lake Nios, located only 100 kilometers away from Lake Manoon. Lake Nios was very similar to Lake Manoon. It's located in the same volcanic field, and the lake was also located in a volcanic crater. However, Lake Nios was five times larger than Lake Monoon, and more than twice as deep.

In the early hours of August 21, 1986, an event similar to that which took place at Lake Monoon occurred. This time, the results were far worse. There were several villages located below the lake in a valley on the side of the crater. Witnesses who came across the scene described it as if it had been hit by a neutron bomb, a bomb that kills people but doesn't damage any property. 1,746 people were killed, along with 3,500 cattle. Most of the dead died in their sleep. Some victims were found as far as 16 miles away from the lake. The few survivors reported a rapid loss of consciousness and the scent of sulfur. Some of the victims had skin damage,

as in Lake Manoon, but there was no evidence of heat or chemical burns. This was too large of an event to have been terrorism. With more victims and more survivors, enough data was gathered to get an idea of what happened. A limnic eruption. A limnic eruption happens when you have dissolved gases at the bottom of a lake. In this case, carbon dioxide was trapped at the bottom of both Lake Nios and Lake Monoon. The carbon dioxide got there from venting from a volcano that sat below the lakes. Over time, the dissolved CO2 built up at the bottom of the lake. CO2's ability to be dissolved in water depends on several factors, including pressure and temperature. The higher the pressure, the more CO2 can be held in the water. And likewise, the colder the water, the more CO2 can be held. In the lakes in question,

they were both deep with much cooler water at the bottom than at the top. In very deep lakes like these, water at the bottom does not mix with water at the top. There's a layer known as a thermocline that separates cooler water from warmer water. The thermocline effectively prevents the cooler water from mixing with the warmer water. Such lakes with layers that do not mix are known as Meromictic lakes. Most lakes are not Meromictic lakes, and the waters will mix at least once per year. Only one lake in a thousand in the world is a Merlemytic lake. The result is that the cooler water, which is under high pressure, just sits at the bottom of the lake, building up an enormous amount of dissolved CO2, which is never released because the water is never disturbed and never

mixed with the water above it. The dissolved CO2 also makes the water heavier, which further prevents the water from mixing with the lighter, warmer water above. However, when the water is disturbed, the results can be dramatic. If you want a relatable example of what can happen, just open a can of soda. The sudden release of pressure causes the dissolved carbon dioxide in the soda to turn into bubbles and come out of the solution. That is basically what happened at both lakes Nios and Lake Monoon, which disturbed the lower layer of water where all the CO2 is being held. The best guess is that it was a landslide on the banks of the lake or some small volcanic event which occurred at the bottom of the lake. When all of the CO2 rich water was disturbed, it changed the pressure and temperature,

which caused a massive release of CO2 gas all at once, just like opening a bottle of soda. The release of the gas further disturbs the water with bubbles, causing even more turbulence, releasing even more gas in a cascade. This giant gas bubble is how the flood that Plutarch spoke of in Lake Albano could have occurred. Once this gas reaches the surface of the lake, it doesn't just float away. CO2 is one and a half times the density of air. Because it's heavier than air, the cloud will just sit there until it dissipates, or it will flow downhill. And that is why the truck at Lake Monoon didn't run. The engine was literally deprived of oxygen. And it also explains, why the men who got out of the truck on the ground died,

but the men at the top of the truck managed to survive. It's also why the villages below the lake crater in Nios were affected because CO2 was heavier than air. The victims never knew what hit them. CO2 is odorless, colorless, and tasteless. They would have been asphyxiated, no different than if they had a plastic bag over their head. Despite the fact that these two events occurred within two years of each other,

this is an extremely rare phenomenon. Only certain lakes are candidates for a limnic eruption. Even then, it might take centuries for enough CO2 to build up to dangerous levels. Once liminologist and geologists had figured out what happened, the next question was identifying other lakes which were candidates and how to figure out ways to prevent it from happening. There actually is a lake that is a candidate for a limnic eruption. And if it were to happen, it would be far worse than any of the other limnic eruptions which had previously occurred. Lake Kivu is on the border of the Democratic Republic of Congo and Rwanda. Lake Kivu is the eighth largest lake in Africa,

and its volume of water is 3,300 times greater than Latt of Lake Nios. And more importantly, there were only 14,000 people who lived in the vicinity of Lake Nios. However, there are 2 million people who live around Lake Kivu. And in the case of Lake Kivu, the gas trapped at the bottom is CO2 and methane. Were there to be a major event at Lake Kivu, there would be an additional risk of methane igniting when it reached the surface. And this is not a theoretical concern. Researchers believe that a limnic eruption may have occurred in Lake Kivu about 5,000 years ago. Over the last 50 years, CO2 levels at the bottom of the lake have increased by over 10%,

and methane levels have increased by over 20%. There is a methane extraction industry on the lake, and the hope is that this is causing enough low-level disturbance to vent the methane as well as some of the CO2. Likewise, a ventilation pipe has been installed at Lake Nios to remove some of the dissolved CO2 at the bottom of the lake. And I'll close by answering a question that some of you might be thinking. If the conditions necessary for a limnic eruption are a deep lake in a volcanic crater in a region with volcanism, there is a very prominent lake that fits the bill. Crater Lake in Oregon, a United States National Park.

Crater Lake is the deepest volcanic crater lake in the world. It's part of the Cascade volcanic arctic arbor. which includes active volcanoes such as Mount St. Helens. So, could a limnic eruption happen at Crater Lake? And the answer is no. And the reason has to do with temperature. All of the lakes I've mentioned so far lie in tropical areas, or at least in places where it seldom snows or freezes. Crater Lake gets a tremendous amount of snow. When the cold freezing snow lands in the lake, it sinks because of its cold temperature. This causes gradual but constant convection in the which slowly circulates the water. It isn't much, but it's enough to prevent a dramatic CO2 buildup.

Limnic eruptions are certainly very dangerous, but they're not something to worry about on your next trip to a lake. Conditions have to be perfect, and there needs to be some sort of event to trigger the eruption, and it takes centuries for the gas to build up to dangerous levels. Moreover, once a potential lake has been identified, steps can be taken to prevent a disaster from occurring. Hopefully, now that we know how limnic eruptions work and can identify lakes that are potential candidates, we can avoid tragedies like Lake No Noon and Lake Nios from ever happening again. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Thor Thompson and Peter Bennett. Today's review comes from listener

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