Recent satellite imagery has revealed that the devastating Nepal flood, which claimed thousands of lives, was primarily caused by a massive bedrock failure beneath the Langtang Lirung glacier. Geomorphologists Kristen Cook and Dan Shugar identified a significant collapse of the mountainside bedrock that dislodged a large chunk of the glacier, leading to an avalanche of ice and rock. This debris surged into the valley, burying villages and dramatically altering the Trishuli River, causing it to widen and become choked with sediment and mud. While previous explanations focused on glacial bursts or earthquakes, the new evidence points to the fundamental instability of the mountain's geological structure. Scientists are exploring the role of weakening permafrost due to climate change as a potential underlying factor contributing to this catastrophic event.

Recent satellite imagery has revealed that the devastating Nepal flood, which claimed thousands of lives, was primarily caused by a massive bedrock failure beneath the Langtang Lirung glacier. Geomorphologists Kristen Cook and Dan Shugar identified a significant collapse of the mountainside bedrock that dislodged a large chunk of the glacier, leading to an avalanche of ice and rock. This debris surged into the valley, burying villages and dramatically altering the Trishuli River, causing it to widen and become choked with sediment and mud. While previous explanations focused on glacial bursts or earthquakes, the new evidence points to the fundamental instability of the mountain's geological structure. Scientists are exploring the role of weakening permafrost due to climate change as a potential underlying factor contributing to this catastrophic event.

Recent satellite imagery has revealed that the devastating Nepal flood, which claimed thousands of lives, was primarily caused by a massive bedrock failure beneath the Langtang Lirung glacier. Geomorphologists Kristen Cook and Dan Shugar identified a significant collapse of the mountainside bedrock that dislodged a large chunk of the glacier, leading to an avalanche of ice and rock. This debris surged into the valley, burying villages and dramatically altering the Trishuli River, causing it to widen and become choked with sediment and mud. While previous explanations focused on glacial bursts or earthquakes, the new evidence points to the fundamental instability of the mountain's geological structure. Scientists are exploring the role of weakening permafrost due to climate change as a potential underlying factor contributing to this catastrophic event.

Earth scientists have finally shed light on how the tragic Nepal flood that claimed thousands of lives happened, with the latest satellite images revealing not just the glacier, but also that the bedrock under the glacier had collapsed.

Geomorphologists Kristen Cook and Dan Shugar claimed that  further analysis of the satellite images from Nepal revealed there was a “big bedrock failure that took part of the glacier with it."

The glacier broke off in a northwest direction and then fell westward into the river flow.

They told AP that clouds and debris obscured initial images from Nepal on Wednesday, so they could only see that part of a glacier had broken off from the Langtang Lirung peak, near the border with Tibet. However, the images taken on Thursday revealed that the bedrock underneath the glacier had collapsed, taking the massive chunk of ice down with it and sending boulders and ice into the valley.

"It shows the whole area without anything hidden, and we could see that, yes, it looked like there was not only this glacier that had failed, but a much larger chunk of the bedrock of the mountainside itself that had given way," said Shugar, associate professor at the University of Calgary. "You have this big bedrock failure that took part of the glacier with it."

Cook said the debris buried villages. It slammed into the valley floor while maintaining its momentum through the steep, narrow valley as ice melted. The expert who works at the Universite Grenoble Alpes in France said water and mud several stories high swept through communities.

“The Trishuli River surged during the flooding. Before and after satellite images of the Kolpurtar, Betrawati and Syapru Besi areas of Nepal show that the river is now much wider, and brown and black, because it overtopped its banks in some areas and filled with debris in others. The change in the colour of the water shows how much sediment the flow was carrying, turning from greenish to very brown because it's full of mud,” Cook said.  

Scientists have earlier cited glacier burst, caused by rapid melting of ice, as a major reason for the devastating floods. Though an earthquake was cited as the reason, the US Geological Survey (USGS) later clarified that the disaster was caused by a "break-off of a glacier."

The International Centre for Integrated Mountain Development (ICIMOD) too believe it was probably an avalanche of ice-rock mixture. The large amount of ice and rock debris fell into the Lendi  Khola, a tributary of the Bhotekoshi River, causing it to flood suddenly, carrying silt and large boulders downstream.

What caused it?

Alton Byers, a mountain geographer at the University of Colorado at Boulder, believes Wednesday's flooding is related to climate change. He said the permafrost that for millennia has helped to  hold together high-altitude rock and ice and soil and glaciers is now weakening and becoming unstable.

However, Cook and Shugar are yet to establish Earth warming as the reason. Though they believe permafrost is melting, destabilising mountainsides, slopes fail, and landslides do occur. 

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