BharatNotes What is GLOF (Glacial Lake Outburst Flood)?
A Glacial Lake Outburst Flood (GLOF) is the sudden release of a large volume of water from a glacial lake when the barrier holding it back — usually a loosely-packed moraine (rock-and-debris) dam or an ice dam — fails. The escaping water mixes with sediment and boulders to form a fast-moving, highly erosive flood that can travel hundreds of kilometres downstream within hours.
A GLOF is usually triggered by an avalanche or rock/ice mass collapsing into the lake (creating a displacement wave that overtops the dam), seismic shaking, extreme rainfall, or progressive dam seepage. It is distinct from a cloudburst or ordinary flash flood, though the three can occur together.
Why GLOFs are increasing
Global warming is causing Himalayan glaciers to retreat, leaving behind new and expanding moraine-dammed lakes. As these lakes grow, the pressure on their unconsolidated dams rises, increasing the probability of breach. The Indian Himalayan region contains a very large number of such lakes; of these, the NDMA has prioritised a set of high-risk lakes for active monitoring and mitigation (NDMA, ongoing).
Major Indian GLOF events
| Event | Year | Key facts (verified) |
|---|---|---|
| Chorabari Lake / Kedarnath disaster | 2013 | Breach of Chorabari glacial lake amid extreme rainfall (375% of normal) intensified the Mandakini flood; part of the wider North India floods (over 6,000 deaths) |
| South Lhonak Lake, Sikkim | 2023 | ~14.7 million m³ of lateral moraine collapsed into the lake (night of 3–4 Oct 2023), releasing ~50 million m³ of water; destroyed the Teesta-III dam at Chungthang; 55 deaths and dozens missing |
India's policy response
- NDMP 2019 recognises GLOF as a climatological disaster; the Geological Survey of India assesses GLOF threats and advises the NDMA.
- NDMA–SDC Guidelines on Management of GLOFs (October 2020) set out risk assessment, monitoring and early-warning best practices.
- National GLOF Risk Mitigation Project (NGRMP) — approved by the Centre with a total outlay of ₹150 crore (Central share ₹135 crore from the National Disaster Mitigation Fund; State share ₹15 crore), covering four States: Arunachal Pradesh, Himachal Pradesh, Sikkim and Uttarakhand (as stated by MoS Home in Lok Sabha, Feb 2025). It funds lake mapping, automatic weather stations and Early Warning Systems, developed with agencies such as C-DAC, ISRO and the Space Applications Centre.
UPSC angle
GLOF sits at the intersection of climate change, disaster management and Himalayan ecology. For Prelims, focus on the mechanism (moraine-dam failure), triggers, and the distinction from cloudbursts. For GS3 Mains, use GLOF to argue the case for robust early-warning systems, careful siting of Himalayan hydropower projects, and ecologically sensitive development in fragile mountain zones — with the Sikkim 2023 and Kedarnath 2013 events as ready case studies.
