Uttarakhand disaster and the Glacial Lake Outburst Floods (GLOF) (TH)

 

Context: Seven persons were killed and over 125 reported missing after a “glacial burst” on Nanda Devi triggered an avalanche and caused flash floods in Rishiganga and Dhauliganga rivers in Chamoli district of Uttarakhand on Sunday (7th Feb 2021).

  • The event has been described as a “glacial burst” by the Centre’s National Crisis Management Committee (NCMC), headed by Cabinet Secretary.

Analysis

  • Environmental experts attributed the Nanda Devi glacial melt to global warming.
  • Glacier retreat and permafrost thaw are projected to decrease the stability of the mountain slopes and increase the number and area of glacier lakes, according to the latest assessment reports of the UN Intergovernmental Panel on Climate Change.
  • Originating from Vasudhara Tal, perhaps the largest glacial lake in Uttarakhand, the Dhauliganga flows in a meandering course, which takes it through the Nanda Devi National Park.
  • Known for its spectacularly beautiful route and white-water rafting, the river turned into a deathly torrent on Sunday after a part of the Nanda Devi glacier broke off and collapsed into it.
  • The Dhauliganga, which merges with the Alaknanda, is one of the several tributaries of the Ganga, as the river flows down from the Himalayas and snakes its way through the plains.

Reminder of Gya glacial lake that outburst in 2014

  • Recently, using remote sensing data, researchers from Germany mapped the evolution of Gya glacial lake that outburst in 2014 and note the cause of the flood.
  • Most interesting was finding the cause of the flood —here the flooding did not happen due to the spillovers due to an avalanche or landslide, rather there was a thawing of the ice cores in the moraine [a field of dirt and rocks that have been pushed along by the glacier as it moves] which drained through the subsurface tunnels.

Glacial Lake Outburst Floods (GLOF)

  • As glaciers retreat, the formation of glacial lakes takes place behind moraine (glacial debris left behind after the ice has retreated), rock or ice dam.
  • In particular moraine dams, which is the most common dam type in the Himalayan region, are potentially weak and can breach suddenly, leading to a discharge up to millions of cubic meters of water and debris.
  • Glacial Lake Outburst Floods (GLOF) is a term used to describe a sudden release of water retained in a glacial lake that can be located in front, at the side, underneath, within, or on top of a glacier.
  • Large lakes located in front of the glacier are mainly dammed by loose moraine and these lakes are generally considered to be potential flood sources.
  • Different types of lakes may have different levels of hazard potential.
  • For instance, moraine-dammed lakes located at the snout of a glacier have a high probability of breaching and thus may have high hazard potential, whereas rock dam’s lakes have little chances of breaching and thus have a lower hazard potential.
  • Much of the damage caused during GLOF events are associated with large amounts of debris / boulders that accompany the floodwaters. 
  • Continued climate change is expected to alter and potentially increase the likelihood of lake outbursts in the future, as:
  1. Glacial lakes grow in size and number,
  2. Stability of steep slopes is weakened due to changes in thermal and mechanical conditions, and
  3. Heavy rainfall increases landslide activity.
  • In total, there are about 9,575 glaciers in the Indian Himalayan Region (IHR), spread across 6 states and union territories i.e., Jammu-Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh.
  • In some cases, cloudbursts can also trigger glacial lake outburst flood events like in the Kedarnath disaster in 2013.
  • While these events have been regarded as a major risk in the central Himalayan region including Sikkim, the arid Trans-Himalayan regions of Ladakh have received attention only recently.
  • Here the glaciers are located at high altitudes not lower than 5,200 m and most glaciers are of small size. Likewise, the glacial lakes are quite small in size.
  • GLOFs are recognized in the National Disaster Management Plan (NDMP) 2019 of India as a potential climatological disaster.
  • Early Warning Systems (EWS) has a prominent role in the international policy agenda and is aligned directly with Priority 4 of the Sendai Framework on Disaster Risk Reduction (DRR), and UN Sustainable Development Goal (SDG) 13 on Climate Action.
  • Four key elements of Early Warning Systems, according to the United Nations Office for Disaster Risk Reduction (UNDRR formerly UNISDR) are:
  1. Risk Knowledge;
  2. Monitoring and Warning Service;
  3. Dissemination and Communication; and
  4. Response Capability.

National Crisis Management Committee (NCMC)

  • For effective implementation of relief measures in the wake of a natural calamity, the Cabinet may set up a committee.
  • On the constitution of such a committee of the Cabinet, the Agriculture Secretary shall provide all necessary information to and seek directions if any, of the Cabinet Committee in all matters concerning relief in the wake of natural calamity and take steps for effective implementation of its directions.
  • In the absence of such a Cabinet Committee, all matter relating to relief shall be reported to the Cabinet Secretary.
  • National Crisis Management Committee (NCMC) has been constituted in the Cabinet Secretariat under the chairmanship of the Cabinet Secretary.

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