Glacial Lake Outburst Flood (GLOF)

A Glacial Lake Outburst Flood (GLOF) is a sudden release of a large volume of water from a glacial lake, usually when the natural dam of moraine (loose rock debris) or ice that holds it back fails. Failure can be triggered by an avalanche or landslide falling into the lake, an earthquake, a cloudburst, or the steady growth of the lake as glaciers melt. The resulting wall of water and debris rushes downstream with immense force, devastating settlements, roads, bridges and hydropower projects. GLOFs are a growing hazard in the Indian Himalayas as warming accelerates glacier retreat.

• 1 A GLOF is the sudden failure of the moraine or ice dam holding back a glacial lake
• 2 Triggers include avalanches, landslides, earthquakes, cloudbursts and glacier retreat enlarging lakes
• 3 India has about 7,500 glacial lakes across 11 Himalayan river basins
• 4 The October 2023 South Lhonak Lake GLOF in Sikkim destroyed the Teesta III hydropower dam
• 5 NDMA runs a National GLOF Risk Mitigation Programme targeting around 189 to 195 high-risk lakes
• 6 Mitigation combines early-warning systems, hazard mapping, lake lowering and automated weather stations
• 7 Climate change is enlarging glacial lakes, raising GLOF frequency and severity

In 2026 NDMA's National GLOF Risk Mitigation Programme intensified monitoring of high-risk Himalayan lakes, with automated weather and water stations in Sikkim relaying data every 10 minutes, following the devastating 2023 South Lhonak GLOF.