Glacial lake outburst floods

In one line: A glacial lake outburst flood (GLOF) is the sudden release of water from a lake dammed by ice or loose glacial debris.

How they form

As glaciers retreat they leave lakes held back by moraines (heaps of rock and soil) or ice. An avalanche, landslide, earthquake or heavy rain can breach the dam and release huge volumes of water and debris in minutes. Lakes can also form on glacier surfaces (supraglacial lakes) or behind landslide debris.

Indian experience

In October 2023 a GLOF from South Lhonak lake in Sikkim swept down the Teesta valley and damaged the Teesta III dam at Chungthang. The National Disaster Management Authority has issued guidelines on managing GLOFs.

What reduces the risk

Mapping and monitoring lakes, lowering water levels through engineered drainage or siphoning, early-warning sensors and keeping settlements and projects out of flood paths. The op-ed asks for continuous monitoring and engineered drainage of glacial lakes.

Where to go next

• Glacier retreat in the Hindu Kush Himalaya
• Hydropower in the Himalayas