The video footage is violent and unsettling.
On Sunday, a torrent of ice, water, mud and debris streamed through a steep river valley in the northern Indian state of Uttarakhand. At least 32 people are dead and almost 200 are missing.
The tragic event occurred in a warming Himalayan region, where glaciers are rapidly melting and retreating. However, glacier experts say the tide likely wasn’t triggered by the collapse or “bursting” of a glacier itself, although the heating climate may have played a role in the larger episode. Earth scientists will learn more in the days and weeks to come, but satellite evidence points to a high altitude landslide causing an avalanche of rock, glacial ice, and snow.
“The disaster was caused by a rock-ice-snow avalanche. We know this with pretty good confidence,” said Mohd Farooq Azam, assistant professor in civil engineering at the Indian Institute of Technology Indore. Azam explores glaciers in the Indian Himalayas.
This avalanche was an extreme event. On a steep ridge at an altitude of about 5,600 meters, a collapsed mountainside pulled down a glacier that towers on the mountain, and the resulting rock-ice-snow mass hit the valley floor at about 3,500 meters. Then the mass all flowed down through the valley, said Azam.
In such a fast-moving avalanche, great friction instantly melts the ice and snow that made up some of the water shown in the videos, explained Joseph Shea, assistant professor of environmental geomatics at the University of Northern British Columbia for years of visiting and exploring Himalayan glaciers.
However, the full source of the huge amount of water seen in the videos is an ongoing investigation, Azam said, noting that Indian scientists are assessing the event at zero. The avalanche could have picked up plenty of ice from the valley floor.
#Breaking A massive sudden flood in Dhauliganga after a huge collapse of the Himalayan glacier in Reni village in Uttarakhand, which now destroyed many riverside houses. This is real #ClimateEmergency.
My thoughts and prayers with the people of Uttarakhand.🙏🏻pic.twitter.com / mMHjyODbq4
– Licypriya Kangujam (@LicypriyaK) February 7, 2021
In a region of fast-melting ice, the question naturally arises how the inexorably warming globe could have contributed to this chaotic event.
Large avalanches occur naturally, especially on steep, glaciated slopes that are prone to falling rocks. “It is very difficult to determine that this particular disaster is only because of climate change,” said Azam. Landslides in the mountains that lead to large debris flows are normal and well documented. A somewhat similar landslide occurred in 2012 in Nepal.
Crucially, however, climate change has increased the melting of glaciers and snow in the Himalayas, Azam said, adding that “the incidence of mountain hazards due to climate change has also increased”.
See also: Where can you see Earth’s dying glaciers?
This could make a major rockfall or landslide around a glacier more likely. As shrinking glaciers retreat, they can leave unstable slopes open and prone to falling rocks, Shea explained. In addition, a warming climate offers more opportunities for high-altitude locations to freeze and thaw, freeze and thaw, etc. This allows water to penetrate cracks, freeze and expand, creating ever larger cracks. “It finally releases these big blocks,” Shea said. At some point, gravity wins.
Both processes could possibly have contributed to the cascading stone-ice-snow avalanche, Shea said.
The ensuing wave of rocks, ice and water eventually flowed through a hydroelectric dam and trapped many workers in a tunnel. Rescues are underway despite lives having been lost.
“It is a tragic event,” said Shea.
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