Glacial Lake Outburst Floods (GLOFs)

Topic: Disaster Management
Source: The Hindu
Context: Recently, several devastating GLOF incidents have occurred in Nepal, including a major event on 8 July 2025, where a Chinese-built friendship bridge was washed away and multiple hydropower projects were rendered non-functional.
This incident has raised serious concerns across the Himalayan region, particularly in India.

What is a Glacial Lake Outburst Flood (GLOF)?
A Glacial Lake Outburst Flood (GLOF) occurs when water from a glacial lake suddenly and rapidly bursts out, typically due to the failure of a moraine (loose glacial debris) or ice dam.
Such floods pose serious threats to human life, infrastructure, and ecosystems.

Causes of GLOFs:

🔹 Natural Causes:

1. Melting of Glaciers and Formation of Lakes:
   Due to rising temperatures in the Himalayas, glaciers are melting rapidly, leading to the formation of unstable glacial lakes.
   ➡️ India alone has more than 7,500 glacial lakes.
2. Ice or Rockfall into the Lake:
   The falling debris displaces water, increasing pressure on the dam, which may burst.
   ➡️ Example: In 2023, an avalanche destabilized South Lhonak Lake in Sikkim.
3. Heavy Rainfall and Cloudbursts:
   Sudden intense rainfall increases water levels rapidly, potentially breaching the moraine dam.
   ➡️ Example: The 2013 Kedarnath disaster was triggered by a cloudburst.
4. Seismic Activity:
   Earthquakes can weaken moraine structures, making them unstable.
   ➡️ Example: Uttarakhand lies in Earthquake Zones IV and V (high risk).
5. Internal Seepage (Piping):
   Gradual seepage within the moraine dam weakens its internal structure, leading to collapse.

🔹 Anthropogenic (Human-Induced) Causes:

1. Unregulated Construction Activities:
   Roads and hydropower projects in glacial regions disturb the fragile ecosystems and increase instability.
   ➡️ Example: In 2023, the Teesta-III dam was destroyed due to lack of a buffer zone.
2. Climate Change:
   Human-driven global warming is accelerating glacial melt, increasing the frequency of GLOFs.
   ➡️ Example: 2023 and 2024 were the hottest years on record globally.

Types of Glacial Lakes in the Himalayas:

1. Supraglacial Lakes:
   Formed on the surface of glaciers from meltwater; highly unstable during summer.
   ➡️ Example: Seen in the July 2024 Nepal GLOF event.
2. Moraine-Dammed Lakes:
   Formed by debris (moraine) along glacier edges; highly unstable and prone to bursting.
   ➡️ Examples: South Lhonak (Sikkim), Tsho Rolpa (Nepal).

Impact of GLOFs:

On Humans and Infrastructure:

• Loss of Human Life:
Sudden floods can submerge entire villages.
🔹 Example: Hundreds died in Kedarnath (2013).

• Damage to Power and Transportation:
Bridges, roads, dams, etc., are destroyed.
🔹 Example: The 1200 MW Teesta-III project was wiped out in 2023.

• Displacement and Livelihood Disruption:
Agriculture, homes, and local economies are severely affected.

On Environment and Ecology:

• Riverbed Aggradation and Channel Shift:
Flood debris raises the riverbed and alters flow direction.
🔹 Example: After the 2023 event, the Teesta River bed rose by several meters.

• Habitat Disruption:
High Himalayan and riparian biodiversity is lost.

• Long-Term Ecological Changes:
Sediment deposition and watercourse changes reduce ecosystem resilience.

Strategies to Mitigate GLOF Risk:

1. Hazard Assessment:

Identification and categorization of 195 high-risk glacial lakes.

2. AWWS (Automatic Weather and Water Stations):

Stations in Sikkim send rainfall, temperature, and water-level data every 10 minutes.

3. Early Warning Systems:

Manual alerts by ITBP in remote areas; digital alerts in Uttarakhand and Arunachal Pradesh.

4. Engineering Interventions:

Use of bathymetry, ERT scans, and construction of artificial drainage channels.

• Bathymetry reveals the shape and depth of a lake from the outside.
• ERT (Electrical Resistivity Tomography) scan shows the lake's internal structure and stability.
  Both techniques together help in forecasting and preventing GLOFs.

5. Community Participation:

Engaging locals in surveys and considering religious sensitivities in planning.

Institutional Initiatives:

• National GLOF Programme (NDMA):
A $20 million plan to classify 195 lakes into 4 risk levels.

• Committee on Disaster Risk Reduction (CoDRR):
Coordination between states, research institutes, and central agencies.

• 16th Finance Commission Plan (2027–31):
Prioritizes GLOF mitigation under climate-resilient infrastructure.

• 2024 Survey of 40 High-Risk Lakes:
Conducted in Ladakh, Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh.

Conclusion:

Glacial Lake Outburst Floods (GLOFs) are an increasing threat in the Indian Himalayas, triggered by rising temperatures, seismic vulnerability, and unplanned development.
India is shifting from reactive relief to technology-driven monitoring and local engagement for risk reduction.
For long-term resilience, investment is needed in early warning systems, cross-border data sharing, and Himalayan climate adaptation.

MCQs and Mains Questions based on GLOFs are provided separately and are useful for UPSC/PSC exams.

📝 Multiple Choice Questions (MCQs):

Q1: Which of the following is not a potential natural cause of a Glacial Lake Outburst Flood (GLOF)?
A) Seismic activity
B) Excessive rainfall
C) Artificial drainage channels
D) Ice or rock falling into the lake
✅ Answer: C) Artificial drainage channels

Q2: How many high-risk lakes have been identified by NDMA for GLOF risk assessment?
A) 75
B) 125
C) 195
D) 250
✅ Answer: C) 195

Q3: What is the ‘ERT Scan’ technique used for?
A) Measuring river flow
B) Forecasting climate change
C) Examining the internal structure of moraine dams
D) Analyzing greenhouse gases
✅ Answer: C) Examining the internal structure of moraine dams

Q4: Which of the following is an example of a moraine-dammed lake?
A) Dal Lake
B) Tsho Rolpa Lake (Nepal)
C) Wular Lake
D) Chilika Lake
✅ Answer: B) Tsho Rolpa Lake (Nepal)

Q5: The Teesta-III project was damaged during which GLOF event?
A) 2013 Kedarnath Flood
B) 2023 Sikkim Flood
C) 2024 Nepal Flood
D) 2025 Ladakh Flood
✅ Answer: B) 2023 Sikkim Flood

📖 Mains Questions and Answers:

Q1: Why are Glacial Lake Outburst Floods (GLOFs) becoming an emerging disaster in the Himalayan region? Suggest remedial measures with reference to India’s current strategy.

Answer:
GLOFs are rapidly emerging as a significant disaster in the Himalayan region due to accelerated glacial melting caused by climate change, leading to unstable lakes. Seismic activities, cloudbursts, and anthropogenic developments like hydropower projects further aggravate the risk.

India’s Current Strategy Includes:

1. Risk Assessment: Identification of 195 high-risk glacial lakes.
2. Early Warning Systems: Alerts through AWWS and ITBP.
3. Engineering Interventions: Use of bathymetry, ERT scans, and artificial drainage channels.
4. Community Involvement: Engaging locals in monitoring and preparedness.
5. Institutional Initiatives: NDMA and CoDRR actions, plans from the Finance Commission.

Recommendations:

• Enhance cross-border data sharing.
• Implement a GLOF-specific climate adaptation policy.
• Expand community awareness campaigns and mock drills.
• Regulate unplanned construction in ecologically sensitive zones.

Q2: How do GLOFs affect humans, infrastructure, and the environment? Explain with examples.

Answer:
GLOFs have multidimensional impacts:

1. On Human Lives:
   • Sudden floods result in loss of life.
     🔹 Example: Hundreds died in the 2013 Kedarnath disaster.
2. On Infrastructure:
   • Destruction of bridges, roads, and hydropower projects.
     🔹 Example: The Teesta-III project was rendered inoperative in 2023.
3. On Displacement and Livelihoods:
   • Affects agriculture and forces migration.
4. On Environment:
   • Riverbeds rise, and water flow is diverted.
     🔹 Example: In 2023, Teesta riverbed rose by several meters.
   • Biodiversity in high-altitude Himalayan ecosystems is impacted.

Conclusion:
GLOF is not merely a water-related disaster but a complex socio-ecological and economic crisis that demands integrated and long-term solutions.