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Ecology & Environment
Mahesh

09/10/23 09:00 AM IST

Sikkim flash floods

In News
  • More than 25 people have been confirmed dead, and many more are missing from a massive flood that resulted from a glacier-lake outburst in Sikkim.
Glacial Lake Outburst
  • Technically called a Glacier Lake Outburst Flood (GLOF), these are instances of large lakes formed from the melting of glaciers, suddenly breaking free of their moraine — natural dams that are formed from rock, sediment and other debris.
  • The South Lhonak glacier, located in north Sikkim, is reportedly one of the fastest retreating glaciers.
  • The glacier receded nearly 2 km in 46 years from 1962 to 2008. It further retreated by ~400 m from 2008 to 2019.
  • There are an estimated 7,500 glaciers in the Himalayas and GLOFs have been associated with major disasters through the years.
  • The 1926 Jammu and Kashmir deluge, the 1981 Kinnaur valley floods in Himachal Pradesh and the 2013 Kedarnath outburst in Uttarakhand as examples of GLOF related disasters.
  • Among the Himalayan States in India, Sikkim has about 80 glaciers more than any other State. Over the years climatologists have warned that they could be responsible for lake outbursts.
Reasons for GLOF
  • Satellite images from the National Remote Sensing Centre, Indian Space Research Organisation suggest around 105 hectares (about 1 square km) of the glacier-fed lake had been drained out.
  • This was on comparing images taken on September 28, when the lake spanned 167 ha and on October 4, the night of the disaster, when it shrunk to 62 ha. On September 17, it was 162 ha.
  • Water-monitoring apparatus maintained by the Central Water Commission (CWC) reports that water levels surged nearly 60 feet above the maximum levels at Sangkalang at 1:30 pm and gushed at nearly 55 kmph.
  • This is, at the very least, thousands of cubic metres of water in a short time and being midnight, gave very little lead time for people downstream to react.
  • The primary reason for the sudden surge appears to be a likely combination of excess rainfall and a GLOF event.
  • The lake is at a height of 5,200 metres with a towering ice-capped feature at about 6,800 metres to the north of and in close proximity to the lake.
  • There is speculation that heavy rainfall might have tipped the moraine to collapse and trigger the flood but meteorological records don’t reveal any evidence of such heavy rain.
Future uncertainty
  • Both the frequency and severity of such events are going to increase exponentially in the future.
  • The Himalayan ecosystem is the most fragile in the world and any disruption in the way we are managing these resources will have a problematic outcome for the people of the region.
  • Rising temperatures are leading to a wetter future and contributing to climate change led extreme events, but it is also disturbing the fragility of the Himalayan ecosystem through hydropower and other dams.
  • GLOF is an outcome of warming of the region and this has been a major risk for the region.
  • Once it is formed, you never know what triggers its outburst.
Source- The Hindu

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