Glacial Lake Outburst Flood (GLOF)
A GLOF occurs when the water contained within a glacial lake is suddenly released, usually because the natural dam holding it back — commonly a moraine (loose rock and sediment) or an ice dam — fails. The trigger can be an avalanche, a landslide, a rock/ice fall into the lake generating a displacement wave, heavy rainfall, or the gradual thinning of an ice dam due to glacier melt. The sudden discharge sends a high-velocity flood wave, often laden with sediment and debris, down the river valley below, capable of destroying settlements, roads, bridges, and hydropower infrastructure far downstream.
- The October 4, 2023 South Lhonak Lake GLOF in North Sikkim released roughly 50 million cubic metres of water and eroded around 270 million cubic metres of sediment, raising Teesta river levels sharply and causing deaths across four Sikkim districts (Mangan, Gangtok, Pakyong, Namchi)
- South Lhonak Lake had been flagged as a dangerous, expanding moraine-dammed lake by scientific studies years before the 2023 breach
- The Himalayan region (India, Nepal, Bhutan, China/Tibet) contains thousands of glacial lakes; studies have identified several dozen as classified "potentially dangerous" for possible outburst
- Glacier retreat due to climate change is increasing both the number and size of glacial lakes across the Hindu Kush Himalaya region
● Tracked since March 31, 2026 · last seen August 29, 2026 · updates as the daily brief publishes
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