Question:
Explain the causes of glacial lake outburst flood.
(UPSC 2025, Paper 1, Geography Optional PYQ)
Answer.
A Glacial Lake Outburst Flood is a sudden, catastrophic release of water from a glacial lake caused by the failure of natural dams, such as moraines, ice, or landslide debris.
These floods are among the most hazardous cryospheric disasters, especially in high-mountain regions such as the Himalayas, the Andes, and the Alps.
Formation of Glacial Lakes:
- Glacial lakes form during glacier retreat due to climate warming.
- Glacier melts and retreats.
- Meltwater accumulates in depressions.
- Natural barriers form, such as moraine (rock debris), Ice dams, and Landslide deposits
- These unstable barriers create potentially dangerous lakes.
Types of Glacial Lakes
- Moraine-dammed lakes (most dangerous)
- Ice-dammed lakes
- Bedrock-dammed lakes
Characteristics of Glacial Lakes
- Located in high-altitude mountain regions
- Contain large volumes of meltwater
- Natural dams are weak and unstable
- Highly sensitive to climate change
- Rapidly expanding due to glacier retreat
Locations of Major Glacial Lake Outburst Flood-Prone Regions
Global Hotspots:
- Himalayas (India, Nepal, Bhutan)
- Andes (Peru, Chile)
- Alps (Europe)
- Alaska
In India:
- South Lhonak Lake (2023 GLOF disaster)
- Chorabari Lake (Uttarakhand – Kedarnath flood 2013)
- Tsho Rolpa (Nepal Himalaya)
Causes of Glacial Lake Outburst Flood:
The following are major causes:
1. Natural Dam Failure (Primary Cause):
Most Glacial Lake Outburst Floods occur due to weak moraine dams.
Reasons:
- Loose, unconsolidated debris
- No cementation
- Internal erosion
This makes dams highly unstable.
2. Rapid Glacier Melting (Climate Change)
Global warming accelerates:
- Ice melt
- Lake expansion
- Water pressure increases
This increases the risk of a sudden dam breach.
3. Ice/ Rock Avalanches into Lakes
When large ice or rock masses fall into lakes:
- Sudden displacement waves form
- Overtopping of the dam occurs
- Dam collapses
This is a major trigger of the Glacial Lake Outburst Flood.
4. Earthquakes
- Seismic activity can:
- Destabilize moraine dams
- Trigger landslides
- Cause sudden dam rupture
Example: Himalayan tectonic zone.
5. Heavy Rainfall & Cloudbursts
Intense rainfall increases:
- Lake water level
- Hydraulic pressure on dams
- Leading to dam failure.
6. Internal Ice Melting (Thermokarst Effect)
Ice cores inside moraine dams melt over time, creating:
- Cavities
- Weak structures
- Sudden collapse risk
Consequences of Glacial Lake Outburst Flood:
- Flash floods
- Infrastructure destruction
- Loss of life
- Sediment deposition
- River course changes
Case Study Example :
South Lhonak Lake Glacial Lake Outburst Flood (2023)
Cause:
- Glacier melting + heavy rainfall
- Moraine dam breach
Impact:
- Teesta River flash flood
- Dam failure downstream
- Severe infrastructure damage
Glacial Lake Outburst Floods are climate-induced mountain hazards resulting from the interaction of glacial retreat, unstable moraine dams, and triggering events like avalanches or earthquakes. With rapid glacier melting in the Himalayas, the risk is increasing, necessitating early warning systems, monitoring, and sustainable mountain development strategies.
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