Context:

• Recently, a devastating glacial lake outburst occurred upstream of Chungthang in the Mangan district, Sikkim resulting in a sudden and alarming rise in the water level of the Teesta River.

What are Glacial Lake Outburst Floods (GLOFs)?

• It is the term scientists use to describe the incident when the water levels of glacial lakes breach their boundaries, causing large amounts of water to flow into nearby streams and rivers resulting in flash floods.
• • For Example: In 2013, in Uttarakhand’s Kedarnath when the region witnessed flash floods along with a GLOF caused by the Chorabari Tal glacial lake.
• An “Inventory and Monitoring of Glacial Lakes / Water Bodies in the Himalayan Region of Indian River Basins”, sponsored by Climate Change Directorate, Central Water Commission, and done by National Remote Sensing Centre during 2011-15, found that there are 352, 283 and 1,393 glacial lakes and water bodies in the Indus, Ganga and Brahmaputra basins respectively.
• GLOFs are recognized in the National Disaster Management Plan (NDMP) 2019 of India as a potential climatological disaster.

Major Cause

• Glacial Retreat: According to NDMA, glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs.
• Landslides: Since glacial lakes are found in mountainous regions, which means landslides or ice avalanches can sometimes fall directly into the lakes and displace the water, causing it to over-top the natural dam and flood downstream.
• Extreme Weather Events: Excessive rainfall, heatwaves that result in rapid snow melting, or other disastrous but natural weather events like earthquakes may also become the reason for a glacial lake outburst that can further lead to flooding..
• Slope Failure: Rapid slope movement into the lake which involves melting ice can accumulate overtime behind dams or any other structure and suddenly be released without any warning. This also leads to GLOFs.

NDMA Guidelines

• Key Strategies for Glacial Lake Risk Reduction:  Risk reduction has to begin with identifying and mapping such lakes, taking structural measures to prevent their sudden breach, and establishing mechanisms to save lives and property in times of a breach.
• Methods for Identifying Potentially Dangerous Glacial Lakes: Potentially dangerous lakes can be identified based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam and surroundings, and other physical conditions.
•  Use of Synthetic-Aperture Radar imagery: NDMA has recommended use of Synthetic-Aperture Radar imagery to automatically detect changes in water bodies, including new lake formations, during the monsoon months.
• Structural Lake Management Strategies: To manage lakes structurally, the NDMA recommends reducing the volume of water with methods such as controlled breaching, pumping or siphoning out water, and making a tunnel through the moraine barrier or under an ice dam.

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