Uttarakhand floods: What happens in a glacial burst?

Many past studies suggest that chunks of freshwater ice are melting from Himalayan snowcaps and glaciers at rapid rate due to global temp rise

The massive rush of floodwater in Uttarakhand's Chamoli district and the ensuing disaster that has claimed 19 lives so far with over 200 missing have raised severe questions about the reasons behind the deluge. Initial reports suggested that it was a glacial burst in the Nanda Devi glacier that caused water to flood the rivers, resulting in destruction downstream.

Uttarakhand Chief Minister Trivendra Singh Rawat has maintained that the exact cause of the floods was still not known. On Monday, a group of scientists from the Snow and Avalanche Study Establishment (SASE) of the Defence Research and Development Organisation (DRDO) were set to visit the region to probe the incident.

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Other than the glacial burst, factors like the effects of the climate change, avalanche, cloudburst, construction in ecologically sensitive areas are being discussed as the possible causes.

What is a glacial burst?

Many studies in the past have suggested that the Himalayan snowcaps and glaciers, large chunks of freshwater ice, are melting at a rapid rate due to a global rise in temperature. One of the effects of the melting ice is the movement of large debris over time and the formation of lakes behind them. This debris acts as a natural dam to a large flow of water and increasing pressure might lead to these "dams" bursting which, in turn, leads to floods known as the glacial lake outburst floods or GLOF.

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These floods can devastate life and livelihoods downstream. Rivers along the way get flooded, breaking bridges and barriers. Thus, experts consider GLOFs a deadly ramification of the worsening climate in the Himalayas.

What caused Uttarakhand's floods?

Initial reports have suggested that it was indeed a GLOF that caused the destruction. Experts, however, have raised doubts over it, claiming that the region does not have any glacial lakes.

While avalanches are common in the region, those alone would not result in the kind of floods currently being witnessed.

"The water has to come from a source, and as of now, we do not know what this source is,” Professor H C Nainwal, a glaciologist at the Hemwati Nandan Bahuguna Garhwal University, told The Indian Express.

Read: Uttarakhand glacier disaster: 25 from Uttar Pradesh missing

Another glaciologist told the publication that there was no information on the presence of a glacial lake. "But if there are indeed no glacial lakes in that area, then Sunday’s event would seem to be a bit of a surprise,” said Argha Banerjee, a glaciologist who works at the Indian Institute of Science Education and Research (IISER) in Pune.

Similar to 2013 Kedarnath floods?

The 2013 Uttarakhand's floods that wreaked havoc in the region were caused due to a phenomenon called 'cloudburst'. Sunday's floods, however, do not match the conditions as it was a different time of the year.

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"Cloudburst would be a rare event during this time of the year. It does look like a GLOF event right now,” Professor A P Dimri of the School of Environmental Sciences at the Jawaharlal Nehru University told the publication.

What could be the other causes?

An avalanche, reported two days ago, may have blocked the water flow in the uphill area resulting in a dam-like situation which subsequently burst under pressure. This could have resulted in a sudden rush of water, Banerjee suggested.

Either way, the devastation stands as a stark reminder of the changing climate in the Himalayas.