NDRF teams carry out rescue operations at tunnel, after a glacier broke off in Joshimath causing a massive flood in the Dhauli Ganga river, in Chamoli.
NDRF teams carry out rescue operations at tunnel, after a glacier broke off in Joshimath causing a massive flood in the Dhauli Ganga river, in Chamoli.
Photo: PTI

The breaking of the Nanda Devi glacier in Uttarakhand's Joshimath had triggered an avalanche and led to a deluge in the Alaknanda river system that washed away hydroelectric stations, houses and more. Over a hundred people are feared dead and rescue operations are currently underway.

The sudden flood in the middle of the day in the Dhauli Ganga, Rishi Ganga and Alaknanda rivers -- all intricately linked tributaries of the Ganga -- triggered widespread panic and large-scale devastation in the high mountain areas. And despite there being many explanations, scientists are not quite certain as to what triggered the sudden surge of water near Chamoli. According to reports, people are now gearing up to travel to the site to ascertain the cause of the incident. The crowd favourite theory appears to be what is referred to as a glacial lake outburst flood or GLOF.

What is glacial lake outburst flood?

When glaciers retreat, it leaves behind a large impression in the ground that then becomes a lake. Known as a moraine, these can weaken as water level rises. According to data shared on the United Nations website, there are several lakes high in the Himalayas that can burst their banks and potentially send millions of gallons of deadly floodwaters swirling down valleys.

As climate change becomes an increasingly bigger concern for the world of today, the glaciers in the area are retreating at a rapid pace. And as they retreat, glacier lakes swell, and additional stress is placed on the mountain ecosystem. Simply put, a glacial lake outburst flood occurs when the dam for these glacial lakes fail.

How can glacial lake outburst flood occur?

The reasons behind a GLOF can vary. From erosion or a buildup of water pressure to an earthquake or an avalance - there are various reasons as to how such a phenomenon can occur.

"Fragmentation of the source glacier, landslides and other processes can trigger displacement waves in the lake, potentially compromising the stability of the dam and resulting in a GLOF. Failure of the dam can also occur due to internal processes, such as water seeping through the structure," explains a page on the official website of the International Centre for Integrated Mountain Development.

What happened in Uttarakhand on Sunday?

It remains unclear as to what exactly led to the events of February 7 -- be it climate change or construction work in the area. What we do know is that a portion of the Nanda Devi glacier broke off in Uttarakhand's Chamoli district on Sunday, triggering an avalanche and a deluge in the Alaknanda river system.

"A team of scientists of DRDO-SASE, flown in last night to Dehradun, is leaving for Joshimath area for surveillance and reconnaissance," a Home Ministry spokesperson said on Monday.

(With inputs from agencies)

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