Scientists have solved the mystery behind India’s devastating flood that killed 200 people in February

chamoli disaster
The destroyed Tapovan Vishnugad hydroelectric plant after a devastating flood on February 7, 2021.

  • A massive slab of ice and rock broke off a glacier in the mountains of northern India in February.
  • New research suggests the slab fell a mile down, resulting in a rare flood that killed 200 people.
  • A warming climate is linked to more glacier-related landslides, so experts expect to see more of such floods.
  • See more stories on Insider’s business page.

Imagine a wall of rock and ice 1,800 feet wide falling the length of four Empire State Buildings stacked end-to-end.

A slab that size is responsible for the disaster in northern India that killed more than 200 people and destroyed two power plants four months ago, according to a new study published Thursday.

Just before dawn on February 7, a massive chunk broke off a glacier on Ronti Peak in the Indian Himalayas. The slab dropped more than a mile into the valley below, from its position roughly 18,000 feet above ground, at almost 134 miles per hour.

As the chunk landed, the rock disintegrated and the ice melted, creating a wall of water and debris that swiftly funneled into the river valley below. From there, the mixture cascaded toward the Rishiganaga and Tapovan hydropower plants in India’s Chamoli district. After a curve in the valley slowed the sludge down, it swept into tunnels underneath the plants at speeds of up to 56 miles per hour, trapping and killing many workers inside.

The severity of the event, known as the Chamoli disaster, initially stumped scientists. Typically, landslides in the region don’t kickstart floods as rapid or lengthy as the one that occurred in February.

“A ‘normal’ dry rock avalanche would not have traveled as far as this one did – in other words, would not have reached either the Rishiganga or Tapovan hydroplants,” Dan Shugar, a geoscientist at the University of Calgary and co-author of the new study, told Insider.

Shugar’s team discovered key elements that could explain the disaster’s severity: The initial avalanche’s composition (about 20% ice and 80% rock), coupled with its mile-long fall, resulted in a hyper-mobile torrent of debris that doomed workers in the valley below.

The researchers calculated that the flood was 27 million cubic meters in volume – enough to cover more than 1,600 football fields in 10 feet of debris and still have some left over.

The flood climbed 722 feet up the valley walls

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A computer model shows the path of the Chamoli rock and ice avalanche down Ronti Peak in February 2021.

Flooding and landslides are not uncommon in Uttarakhand, the area of northern India where Chamoli is located. In 2013, heavy rainfall set off devastating floods in the area than killed up to 5,700 people.

After the February disaster, experts initially thought a lake near the top of Ronti Peak had burst after the chunks of glacier holding it together cracked or broke off. Some glacial lakes can hold hundreds of millions of cubic meters of water.

But satellite imagery showed there were no such lakes along the debris flow’s path.

By analyzing maps of the valleys’ terrain, video footage of the event, and earthquake data in the area, Shugar’s team was able to reconstruct what happened.

The chunk of glacier that broke off Ronti Peak in the early morning was, on average, 262 feet thick. When it touched down at the mountain’s base, the slab flattened a section of nearby forest, and threw a thick dust cloud into air. The impact with the valley floor was so violent that the rock and ice therein blended together to form a flood that climbed 722 feet up the valley walls.

It was “almost the ‘optimal’ combination” for melting glacier ice, Holger Frey, a glaciologist at the University of Zurich in Switzerland, told Insider. The massive flood, he added, “facilitated the large reach and destructive nature of this disastrous event.”

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The damaged Dhauliganga hydropower project at Reni village in the Chamoli district of Uttarakhand, India after part of a glacier broke off on February 7, 2021.

‘It’s only a matter of time’ until a disaster like this happens again

The flood caught workers at the hydroplants in Chamoli by surprise.

But according to the study, an early warning system could have given workers six to 10 minutes of notice before the flood reached them. Seismic sensors – which monitor rumblings in the Earth for signs of earthquakes or shifting rock – can detect when an avalanche happens and let workers know if a flood is on its way.

Even if the Chamoli disaster couldn’t have been prevented, Frey said, “a well-designed warning system should be able to warn workers at these plants and allow them to seek safe grounds.”

After all, the conditions that led to the Chamoli disaster aren’t going to disappear any time soon.

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People inspect a site near the damaged Dhauliganga hydropower project.

Evidence from other mountainous regions, like Alaska, suggest glacier-related landslides are increasing in frequency as the climate warms, according to Shugar.

“I expect this would be similar in high mountain Asia,” he said.

Rising air and surface temperatures are linked to more instability in glaciers and an increasing likelihood of landslides high in the mountains. The warmer the Earth becomes, the more glaciers shrink.

“It’s only a matter of time before the next such massive event will happen somewhere in the Himalayas,” Frey said in a press release.

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Decades ago, 9 Russian hikers mysteriously fled their tent and froze to death. A new study sheds light on the cold case.

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A view of a tent rescuers found on February 26, 1959 in the Dyatlov pass. The tent had been cut open from the inside, and most of the campers had fled in socks or barefoot.

  • Nine Russian hikers died mysteriously in the Ural Mountains in 1959.
  • Some bodies were found shoeless, barely clothed, and far from their tent. Most died of hypothermia.
  • A new study suggests a slab avalanche caused by accumulating snow crushed their tent in the night.
  • Visit the Business section of Insider for more stories.

One day into an expedition to the mountains of northern Russia, Yuri Yudin, an avid skier and student at the Ural Polytechnic Institute, felt a pain in his lower back. His sciatic nerve had flared up, and it forced him to leave his group and turn around.

The decision saved his life.

The nine remaining members of the expedition continued hiking and cross-country skiing toward a mountain called Gora Otorten. Then on February 1, 1959, five days after Yudin left, they all died mysteriously.

Rescuers found the group’s large tent, which had been cut open from the inside, nearly four weeks later. The bodies were discovered up to a mile away, down the mountain, some clad in only socks and underwear. Something had caused the hikers to flee shoeless from their tent in temperatures of minus 13 degrees Fahrenheit (minus 25 degrees Celsius).

The “Dyatlov Pass Incident” – named after Igor Dyatlov, the group’s leader – became one of Russia’s most infamous cold cases. The hikers’ immediate causes of death were eventually determined: Six died of hypothermia, and three from blunt force trauma to their chest and head. But the cause of the disaster remained a mystery.

Now, more than 60 years later, a scientific analysis offers an explanation for what happened to Dyatlov’s crew. A study published last month suggests that a small but deadly slab avalanche occurred while the hikers were sleeping. Unlike the snow avalanches typically depicted in movies, a slab avalanche is when a large block of ice slides down a slope. Such a slab crushed part of the hikers’ tent, injuring three of them and forcing the group to flee.

Previous evidence didn’t favor the avalanche theory

Igor Dyatlov Pass
Igor Dyatlov, one of the nine hikers who died during the Dyatlov Pass incident in 1959.

The hikers had set up camp on the slopes of Kholat Saykhl – which translates to “Dead Mountain” in the local Mansi language. They were 12 miles south of their intended destination in the northern Ural mountains.

A photograph recovered from a camera found around the neck of one of the hikers suggests the group pitched camp and ate dinner together on the evening of February 1, 1959. Forensic evidence supports that timeline. 

After the bodies were found, a three-month government investigation determined that a “compelling natural force” had caused the hikers’ deaths, but it didn’t explain what that force was. Their families were left without answers.

Since then, conspiracy theories have run the gamut from a Yeti attack to a run-in with aliens. 

Last picture of the Dyatlov group.Courtesy of the Dyatlov Memorial Foundation
The last photo ever taken of the hikers involved in the Dyatlov Pass incident before they died.

While an avalanche seems like an obvious explanation, it was considered unlikely for years, according to Alexander Puzrin, who co-authored the new study.

“There were several issues with that theory,” Puzrin, a geotechnical engineer from the Swiss Federal Institute of Technology in Zurich, told Insider. 

For one, the rescue team didn’t find any evidence that an avalanche had occurred. It hadn’t snowed that night, which can kickstart an avalanche. More importantly, the angle of the slope on which the hikers pitched their tent wasn’t steep enough for a snow-slide. Avalanches typically happen on slopes of at least 30 degrees.

The hikers’ injuries, too, were uncharacteristic of typical avalanche victims.

Still, Puzrin wasn’t the first to determine that an avalanche must have been to blame. The Investigative Committee of the Russian Federation reopened an investigation into the incident in 2015 and found that an avalanche killed the group. An independent investigation by the Russian Public Prosecutor’s Office, opened in 2019, came to the same conclusion.

dyatlov investigation
Andrei Kuryanov, a Russian federal spokesman, during a press conference announcing that the investigation of the Dyatlov Pass Incident case would be reopened in February 2019.

But none of the investigators offered details.

“They didn’t release the data,” Johan Gaume, Puzrin’s co-author, told Insider. Gaume leads the Snow and Avalanche Simulation Laboratory at the Swiss Federal Institute of Technology Lausanne. “If you say was an avalanche to the relatives without that, how can they trust you?”

That’s the gap the new study fills.

Strong winds doomed the group

By calculating the time between sunset on February 1 and the moment when several of the hikers’ watches stopped, the study authors determined that the group didn’t flee their tent until between 9.5 and 13.5 hours after they’d pitched it, long after they’d eaten and gone to sleep.

The researchers worked out a theory: The hikers had cut into the mountain to create a flat surface for their tent (as shown below). But the slope where they were camping concealed a bit of terrain that was steeper than it seemed, which would enable an overlying slab to slough off under the right conditions.

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An artist’s depiction of the Dyatlov group’s tent installed on a flat surface made from cutting into the slope.

Puzrin’s mathematical models suggest that if enough snow had accumulated on the slope above the tent, a slab could indeed have broken off and slid down. Given that weather records showed it hadn’t snowed that night, the extra snow must have come from strong katabatic winds, the researchers determined – gusts that push air down a slope. These winds likely blew snow down the mountain, where it accumulated on the slope above the tent.

“At a certain point, a crack could have formed and propagated, causing the snow slab to release,” Puzrin said in a press release. Picture a chunk of snow sliding off a gable roof to the ground below.

This wasn’t the hikers’ fault, Puzrin noted: It was the product of compounding coincidences. Had the hikers chiseled away at the mountain slope in a different spot, or had the wind been weaker, there wouldn’t have been an avalanche.

“If they didn’t make the cut, nothing would have happened,” Puzrin said. “But if not for the strong wind or special topography, it wouldn’t have failed and they would’ve woken up and become grandmothers and grandfathers.”

Car-crash tests offered insight into the hikers’ injuries

A dog searches for survivors during a life-saving exercise after avalanche at the Glacier 3000 in Les Diablerets, Switzerland, December 6, 2019. REUTERS/Denis Balibouse
Swiss rescue teams take part in a life-saving exercise after an avalanche at the Glacier 3000 in Les Diablerets, Switzerland, December 6, 2019.

The other counterargument to the avalanche hypothesis was the hikers’ injuries. Broken ribs and fractured skulls aren’t usual outcomes for people caught in avalanches. Typically, avalanche victims asphyxiate to death.

But it’s a different story “if you’re sleeping on the floor of the tent on top of your skis and a 300-kilogram [660-pound] block of snow lands on you,” Gaume said. 

To model what injuries from a slab avalanche would look like, Gaume and Puzrin borrowed data from the automotive industry. In the 1970s, GM took 100 cadavers and hit them with various blocks of different masses at different velocities to model car crashes. The results showed what a prone body would look like if it had been lying on a solid surface then hit with a 16-foot-long, heavy slab. Those injuries would be similar to the ones on the dead hikers, it turned out.

“The injuries would be serious, but not immediately fatal,” Gaume said. That explains how all nine expedition members were able to leave the tent. 

A ‘banal and normal’ answer to a decades-long cold case

Russia_edcp_relief_location_map dyatlov
The location of Dyatlov Pass in Russia.

The Dyatlov Pass mystery became a part of Russian folklore, Puzrin said. Just last year, a series called Pereval Dyatlova rekindled public interest. The show went through various conspiracy theories, including supernatural forces and a romantic spat between the hikers that turned violent. The last episode was about a slab avalanche akin to the one described in the new study.  

“People don’t like something as banal or normal as an avalanche to explain something like this with so many conspiracy theories around it,” Gaume said.

Puzrin added: “We were concerned the reaction in Russia would be ‘thank you for nothing.'”

dyatlov pass
Nine skiers in February 1959 who went on an expedition to Dyatlov Pass and died.

But their analysis still doesn’t address every oddity of the incident. Some of the dead hikers’ clothes had traces of radioactivity, and another group of hikers reported seeing orange spheres in the sky above Dead Mountain on the night Dyatlov’s crew died. (This fueled speculation that UFOs were involved.)

What’s more, two of the bodies were missing eyes and one had no tongue. According to Gaume, however, “one could easily imagine” that during the 26 days before rescuers found the bodies, wildlife gnawed on the remains.

The hikers’ barely clad state, Gaume added, could be attributed to the fact that they panicked.

“Maybe they were afraid of a second avalanche, and didn’t take time to grab their clothes.”

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