Glacial Lake Outburst Flood (GLOF)

• Definition: A GLOF is the sudden release of a large volume of water from a glacial lake, generally due to failure, overtopping or breaching of its natural dam.
• Natural Dam: The lake may be impounded by moraine, glacier ice or bedrock.
• Triggers:
  • Ice/rock avalanche into the lake
  • Landslide
  • Heavy rainfall
  • Earthquake
  • Rapid glacier melting
  • Failure/erosion of moraine dam
• Impact: Sudden discharge of water, often mixed with sediment, rocks and debris, can produce highly destructive downstream floods.
• Climate Change Link: Glacier retreat can enlarge existing glacial lakes and create new ones, increasing potential GLOF risk in vulnerable Himalayan valleys.
• Himalayan Significance: The Hindu Kush Himalaya (HKH) is particularly vulnerable because of its glaciers, steep terrain and densely populated downstream valleys.
• India: GLOF risk is especially relevant to Sikkim, Himachal Pradesh, Uttarakhand, Arunachal Pradesh and Ladakh.
• Recent Indian Examples:
  • South Lhonak Lake, Sikkim — 2023: Major GLOF caused severe downstream flooding.
  • Chamoli, Uttarakhand — 2021: Glacier-related flash flood involving massive ice/rock debris.
• Technology for Monitoring: Satellite remote sensing, GIS, hydrological monitoring, drones and early-warning systems can help identify potentially dangerous glacial lakes.

UPSC Prelims Question — English

Q. With reference to Glacial Lake Outburst Floods (GLOFs), consider the following statements:

1. GLOFs involve the sudden release of water stored in a glacial lake.
2. A glacial lake may be impounded by a moraine or glacier ice.
3. Every flash flood caused by glacier collapse is necessarily a GLOF.
4. GLOFs can carry large quantities of sediment and debris downstream.

Which of the statements given above are correct?

A. 1 and 2 only
B. 1, 2 and 4 only
C. 2 and 3 only
D. 1, 2, 3 and 4

Answer: B. 1, 2 and 4 only

Explanation: A GLOF specifically involves the sudden release of water from a glacial lake. A direct collapse of glacier ice or rock can generate a flash flood without a glacial lake outburst; hence, Statement 3 is incorrect.