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Glacial ‘tooth’ caused deadly February flash flood in India

A general view shows the remains of a dam along a river in Tapovan of the Chamoli district on February 8, 2021 destroyed as a result of the flash flood.

A general view shows the remains of a dam along a river in Tapovan of the Chamoli district on February 8, 2021 destroyed as a result of the flash flood.
Photo: Sajjad Hussein / AFP (Getty Images)

In February, a massive avalanche ravaged a mountain valley in the state of Uttarakhand in northern India, causing flash floods and mudslides. A new study discovered that debris broke away from a glacier above the valley and disintegrated so quickly that the resulting friction melted the ice around it, causing the huge wave of deadly water.

Spectacular footage of the disaster showed a torrent of debris and water rushing down a river and crashing through a dam. The disaster left 200 people dead, including many workers from the two hydroelectric plants along the river which collapsed and trapped people inside.

Early local reports indicated that a piece of the nearby Nanda Devi glacier had ruptured and fell into a nearby river, causing the avalanche. But there was “a lot of confusion and a lot of really bad terminology” in the media in the days after the flooding, said Dan Shugar, associate professor of geosciences at the University of Calgary and co-author of the short story. study. He and a team of other scientists came together to figure out what really happened.

The resulting study, published this week in Science, used satellite and seismic data, video footage and digital modeling to reconstruct the causes of the crisis. The two things scientists tried to solve in this glacial thriller were, Shugar said, “what was the cause of the event and where did all the water come from?”

Usually, water surges like those seen in February are associated with what is called a glacial lake overflowing. These occur when the natural dam at the muzzle of a glacier behind which lakes can form weakens and eventually fails, sending a wall of water down the valley. But there was no evidence of a glacial lake in satellite imagery, nor any telltale fingerprints on the landscape typically left by glacial lake flooding. Shugar noticed a “cloud of dust snaking along the valley” which he saw in the first satellite images as well as pieces of the mountain which apparently disappeared the day before and the day before the event.

“We have a landslide playing a role here, but then where does all the water come from? Shugar said.

Shugar and his team went through all possible sources of this wave of water, cutting them off one by one. Using all the information available, the most likely scenario they’ve landed on is pretty wild. Of the 27 million cubic meters of material that tumbled down the mountain that day, about 80% was bedrock, while only 20% was ice. This means that what has fallen is called a hanging glacier.

“It’s stuck to the side of a mountain, very steep, almost like a tooth of ice stuck to the side of the mountain,” said Shugar. The collapse of the hanging glaciers is not entirely unusual – at this particular site, another hanging glacier had collapsed a few years ago – but the fall in this amount of bedrock is new.

“When the bedrock falls, it quickly disintegrates [from] more or less solid bedrock down to clay particles extremely quickly, ”Shugar said. “The frictional energy that is produced and released is in the form of heat. Calculations by some of my co-authors showed that the rock-to-ice ratio here combined with the incredible drop height we saw was almost enough to melt all the ice.

In other words, the bedrock collapsed so quickly that the heat melted the ice, causing a huge stream of water that fell with the wave of dust. When most people these days hear that a glacial collapse caused a disaster, their brains automatically turn to climate change, but it can be a case of geological drifts without absolute proof that warming has played a role. Shugar said her team didn’t have the kind of location-specific temperature data they would need to permanently link the collapse to climate change.

“It’s really, really hard to unequivocally link this to climate change. We can’t do it, ”he said. “Climate change may have played a role here, but we cannot conclusively say ‘yes’ or’ no. “”

However, the disaster highlights just how unpredictable glacial regions can be, especially when humans build infrastructure in sensitive areas. The enormous death toll and the massive wave of destruction are a harbinger for the rapidly changing and increasingly unstable glacial regions.

“As the climate changes, we expect bigger dangerous events like this, and when people get in the way, they will become disasters,” Shugar said. “Maybe the hanging glacier in this case played a role in introducing more meltwater down the slope, maybe the permafrost played a role, we can’t really say. But in the future, we expect more of these kinds of disasters. When we think of large-scale infrastructure, whether it’s a hydroelectric power station in Asia or a pipeline in North America, we have to think not only about what these mountainous landscapes look like today, but what they will look like in 20 years, 50 years. We must think of these landscapes as dynamic.

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