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What is a glacier outburst flood and why does it occur?

Topics Covered: Disaster and disaster management.

What is a glacier outburst flood and why does it occur?


Context:

Parts of Uttarakhand recently witnessed massive flooding after a chunk of the Nanda Devi glacier broke off at Joshimath in Uttarakhand’s Chamoli district.

  • Bringing back haunting memories of the 2013 Kedarnath calamity, the glacier break caused large-scale devastation in the upper reaches of the ecologically fragile Himalaya.
  • As per the available information, over 150 labourers working at a power project in Tapovan-Reni are missing.

What is glacial lake outburst flood (GLOF)?

It is an outburst that happens when a dam containing a glacial lake fails.

GLOFs have three main features:

  1. They involve sudden (and sometimes cyclic) releases of water.
  2. They tend to be rapid events, lasting hours to days.
  3. They result in large downstream river discharges (which often increase by an order of magnitude).

Why does a glacier break?

  1. Erosion.
  2. A build-up of water pressure.
  3. An avalanche of snow or rocks.
  4. An earthquake under the ice.
  5. Massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.

Impact:

Although glacier lakes can vary in volume, they are known to hold millions to hundreds of millions of cubic metres of water and a failure to contain ice or glacial sediment can result in water being released even for days.

What is Nanda Devi glacier?

The Nanda Devi glacier forms part of the second-highest mountain in India — the Nanda Devi mountain.

While it the second-highest after Kangchenjunga, it is the highest mountain located entirely within the country as Kangchenjunga lies on the border of India and Nepal.

Sources: the Hindu.