Glacial Burst

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    Glacial Burst

    In News: Recently, a glacial burst on Nanda Devi has triggered an avalanche and caused flash floods in Rishiganga and Dhauliganga rivers in Chamoli district of Uttarakhand.

     

    Major Points:

    • It washed away at least two hydroelectric power projects, the 13.2 MW Rishiganga hydroelectric power project and 520 MW NTPC Tapovan-Vishnugad project (also known as Rishi Ganga Project) on the Dhauliganga river, a tributary of the Alakananda.
    • Possible Causes:
      • A part of the Nanda Devi glacier, which broke off and collapsed in the lake, which surprisingly occurred at the edge of the winter season.
        • Satellite and Google Earth images do not show a glacial lake near the region, but there is a possibility that there may be a water pocket in the region.
          • Water pockets are lakes inside the glaciers, which may have erupted leading to this event.
      • Environmental experts have attributed the glacial melt to global warming and climate change.
        • Climate change has driven erratic weather patterns like increased snowfall and rainfall, warmer winters have led to the melting of a lot of snow.
        • The thermal profile of ice has been increasing. Earlier, the temperature of ice ranged from -6°C to -20°C and now it is -2°C, making it more susceptible to melting.
      • The average temperature in the northwestern Himalaya has risen by 0.66°C since 1991 (an increase much higher than the global average).
        • The higher Himalaya became even warmer on average in the same period.

                                                (Image Courtesy: The Wire)

    • Concerns:
      • According to the UN Intergovernmental Panel on Climate Change (IPCC), glacier retreat and permafrost thaw are projected to decrease the stability of mountain slopes and increase the number and area of glacier lakes.
      • Also, the number and area of glacier lakes will continue to increase in most regions in the coming decades. Consequently, new lakes will develop closer to steep and potentially unstable mountain walls where lake outbursts can be more easily triggered.
      • Environmentalists have always warned against the construction of dams as there is always a chance of flooding in the eco-sensitive Himalayan region.

    Glacial Burst:

    • These are also known as the Glacial Lake Outburst Flood (GLOF).
    • When glaciers retreat, they leave a space which becomes a glacial lake being filled with water. When such a lake breaches, it is known as GLOF.
    • It can occur for a number of reasons like erosion, a build-up of water pressure, an avalanche of snow or rocks, and also an earthquake under the ice. It can also be triggered by massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.
    • GLOFs have three main features:
      • Involve sudden (and sometimes cyclic) releases of water.
      • Tend to be rapid events, lasting hours to days.
      • Result in large downstream river discharges (which often increase by an order of magnitude).

    Avalanche:

    • An avalanche is falling masses of snow and ice which gathers pace as it comes down the slope.
    • These occur naturally as well as due to anthropogenic factors.
      • Underlying snowpack, overloaded by a quick deluge of snow, can cause a weak layer beneath the overlying snow slab to fracture naturally. Earthquakes can also trigger strong avalanches.
      • Human-triggered avalanches start when somebody walks or rides over a slab with an underlying weak layer.

    Flash Floods:

    • Flash Floods are highly localized events of short duration with a very high peak and usually have less than six hours between the occurrence of the rainfall and peak flood.
    • The flood situation worsens in the presence of choked drainage lines or encroachments obstructing the natural flow of water.

    Nanda Devi Glacier:

    • It forms part of the second-highest mountain in India, the Nanda Devi mountain.
      • While it is the second-highest after Kangchenjunga, it is the highest mountain located entirely within the country as Kanchenjunga lies on the border of India and Nepal.
    • On the northern side of the Nanda Devi lies the Uttari Nanda Devi Glacier and to the southwest lies the Dakkhini Nanda Devi Glacier. All of these glaciers drain west into the Rishiganga.

    Dhauliganga and Rishi Ganga:

    • Dhauliganga is one of the important tributaries of Alaknanda, the other being the Nandakini, Pindar, Mandakini and Bhagirathi.
    • Dhauliganga is joined by Rishiganga river at Raini where the disaster at the power project dam took place.
      • Raini was one of the principal sites of the iconic Chipko Movement in the 1970s.
    • According to the South Asia Network on Dams, Rivers and People (a think tank) under construction hydroelectric power projects threaten about 50% of the Dhauliganga’s length.

    Major Natural Disasters in the Region:

                                                (Image Courtesy: The Hindu)

    Source: TH

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