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Three things to know about the disastrous flood in India

On February 7, a flood rose up a river in the Indian state of the Himalayas, Uttarakhand, killing at least 30 people and washing away two hydroelectric power plants.

While rescue workers are searching for more than 100 people who are still missing, officials and scientists are trying to unravel the causes of the flash flood. Did a glacier collapse on top of the mountains and release a huge plug of icy melted water that spilled into the river? Or was the culprit a landslide that then triggered an avalanche? And what link, if any, could these events have with a changing climate?

Here are three things about what may have caused the disaster in Uttarakhand.

1. One possible culprit was the sudden rupture of a glacier high in the mountains.

News immediately after the disaster suggested that the floods were caused by the sudden overflow of a glacial lake at the top of the mountain, an event called a glacial lake eruption flood.

“It’s probably too early to know what exactly happened,” says Anjal Prakash, director of research at the Bharti Institute of Public Policy at the Indian School of Business in Hyderabad. Satellite images show that a section of a glacier was broken, but it is still unknown how that rupture is related to subsequent flooding. One possibility is that the glacier retained a lake of molten water and that heavy snowfall in the region two days earlier added enough volume to the lake for the water to force its way out, breaking the glacier and rising into nearby rivers.

This scenario is certainly in line with the known dangers to the region. “These mountains are very fragile,” says Prakash, who was also lead author of the 2019 Intergovernmental Panel on Climate Change’s special report on the oceans and cryosphere, the icy places on Earth. But, he points out, there is still not much data on the ground to help clarify the events. "Efforts are still focused on relief at this time."

2. Instead you may be to blame for a detachment.

Other researchers argue that the disaster was not caused at all by a glacial lake flood. Instead, says Daniel Shugar, a geomorphologist at the University of Calgary in Canada, satellite images taken during the disaster show the telltale marks of a landslide: a dark scar meandering through the white snow and clouds of dust clogging the air. up. “You could see this train of dust in the valley, and that’s common for a very large landslide,” Shugar says.

“WOW,” he wrote on Twitter on the morning of Feb. 7, posting satellite shots side-by-side of a dark area of ​​possible “massive dust deposition,” in contrast to the same snowy, pristine region of the day before.

Landslides, the sudden failure of a slope, the throwing of rocks and sediments downwards, can be triggered from any type of earthquake to an intense deluge of rain. In the high, snow-capped mountains, cycles of freezing, thawing, and ice again can also begin to break the ground; ice-filled cracks can slowly widen over time, creating the stage for a sudden failure and then disaster.

Satellite images appear to clearly point to a landslide, rather than a typical glacial lake overflow, Shugar says. The force of the landslide could have broken that piece of hanging glacier, he says. Another line of evidence against a sudden eruption of the lake is that “there were no lakes of any size visible” in the satellite images taken over the region.

However, a peripheral question for this hypothesis is where the floodwaters came from. It could be that one of the rivers draining down the mountain was briefly dammed by falling rocks; a sudden release of that dam could send a large plug of river water quickly and disastrously down. “But that’s a pure guess at the moment,” Shugar says.

3. It is still unclear whether climate change has played a role in the disaster.

The risk of flooding from glacial lake eruptions and landslides related to freezing and thawing in the high mountains of Asia has increased due to climate change. At first glance, “it was a weather event,” Prakash says. "But the data keeps coming."

The region, which includes the Hindu Kush Himalayan mountains and the Tibetan Plateau, "has been a hot spot of climate change for quite some time," says Prakash. The region is often called the third largest on Earth, because ice and snow reserves in the Himalayan watershed amount to the largest freshwater reserves outside the polar regions. The region is the source of 10 major river systems that provide water to nearly 2 billion people.

Climate change reports have warned that warming not only threatens this water supply, but also increases the likelihood of natural hazards (SN: 29/05/19). In the 2019 special report of the Intergovernmental Panel on Climate Change on the oceans and cryosphere, scientists noted that glacier retreat, snowmelt and permafrost thawing are making mountain slopes more unstable and also increasing the number of lakes. glaciers, increasing the likelihood of a sudden and catastrophic. fallo (SN: 25/09/19).

A full 2019 assessment focusing on the impacts of climate change on Asia's high mountains found that the region's glaciers have receded much faster in the last decade than expected, says Prakash, "and that's alarming to us." Here’s another way to see it: glaciers retreat twice as fast as in the late 20th century (SN: 19/06/19).

Glacier-related landslides in the region have also become increasingly common in the last decade, as the region heats up and destabilizing freeze-thaw cycles within the ground occur increasingly higher on the slopes.

But in the case of this particular disaster, Shugar says, it’s hard to say conclusively at this point what role climate change could have played or even what specific event may have triggered a landslide. “Sometimes there is no trigger; sometimes it's just time, "he says." Or we just don't understand the trigger. "

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