Glacial Lake Outburst Floods (GLOFs)
Kartavya Desk Staff
Syllabus: Disaster Management
Source: TH
Context: Nepal recently witnessed multiple catastrophic GLOF events, including one on July 8, 2025, that washed away a key China-built friendship bridge and crippled hydropower projects.
• This has raised alarm across the Himalayan region, including India, where warming temperatures are increasing the risk of similar events in glacial lake belts of Sikkim, Ladakh, and Uttarakhand.
About Glacial Lake Outburst Floods (GLOFs):
What is a Glacial Lake Outburst Flood (GLOF)?
A GLOF is the sudden release of water from a glacial lake, often caused by the collapse of moraine or ice dams. These floods are high-velocity and high-volume, posing serious risks to life, infrastructure, and the ecosystem, particularly in the Indian Himalayan Region (IHR).
Causes of GLOFs:
Natural Causes:
• Glacial Retreat and Lake Formation: Rising temperatures in the Himalayas are accelerating glacial melt, leading to formation of unstable moraine-dammed or supraglacial lakes.
E.g. India has over 7,500 glacial lakes, many above 4,500 m altitude.
• Ice or Rock Avalanches: Falling ice or rock into a glacial lake displaces water and causes waves that breach the dam.
E.g. South Lhonak lake in Sikkim (2023) was destabilized by an avalanche.
• Heavy Rainfall and Cloudbursts: Sudden, intense rains increase water volume rapidly, stressing moraine dams.
E.g. Kedarnath GLOF (2013) followed a cloudburst.
• Seismic Activity: Earthquakes can destabilize loose moraine structures, leading to dam breaches.
E.g. Uttarakhand is in Seismic Zone IV & V—highly vulnerable.
• Internal Seepage (Piping): Slow erosion from within moraine dams due to seepage weakens the dam over time.
Anthropogenic Causes:
• Unregulated Construction: Hydropower and road projects near glacial zones disturb fragile landscapes.
E.g. Teesta-III Dam was destroyed in 2023 due to lack of buffer zones.
• Climate Change: Human-induced emissions are accelerating glacial melt rates globally, increasing GLOF events.
E.g. 2023 and 2024 were the hottest years on record globally.
Types of Glacial Lakes in the Himalayas
• Supraglacial Lakes: Form on top of glaciers from meltwater. Highly unstable during summer.
E.g. Seen frequently on Tibetan side, as in the July 2024 Nepal GLOF.
• Moraine-Dammed Lakes: Form at glacier snouts, dammed by loose debris. Prone to breach due to low cohesion.
E.g. South Lhonak (Sikkim), Tsho Rolpa (Nepal).
Impacts of GLOFs:
On Human Settlements and Infrastructure:
• Loss of Life: Sudden floods can drown entire villages.
E.g. Kedarnath (2013) saw hundreds of deaths.
• Damage to Hydropower & Transport: GLOFs damage bridges, roads, dams, and disrupt energy supply.
E.g. 1200 MW Teesta-III project wiped out in 2023.
• Displacement and Livelihood Loss: Affects agriculture, homes, and leads to economic insecurity.
On Environment and Ecology:
• Riverbed Silting and Course Shifts: Excessive debris raises riverbeds and alters river flow.
E.g. Teesta riverbed has risen by several metres post-2023 GLOF.
• Habitat Disruption: Biodiversity in alpine and riparian zones gets fragmented or destroyed.
• Long-Term Ecosystem Changes: Persistent sedimentation and changing water regimes reduce ecosystem resilience.
NDMA’s 5-Point Strategy to Mitigate GLOF Risks:
• Hazard Assessment: Identified 195 high-risk glacial lakes and classified them by size, dam type, and downstream vulnerability.
• AWWS (Automated Weather & Water Stations) Installation: Automated stations in Sikkim relay real-time data every 10 minutes on rainfall, temperature, and water levels.
• Early Warning Systems (EWS): Manual alerts via ITBP in remote zones; digital multilingual alerts piloted in Uttarakhand and Arunachal.
• Engineering Interventions: Conducted bathymetry and ERT scans; built artificial channels to safely drain lake water.
• Community Involvement: Engaged locals in surveys; addressed religious sensitivities to ensure smooth implementation.
India’s Measures to Mitigate GLOF Risk:
• Institutional Mechanisms:
• NDMA’s National GLOF Programme: A $20 million initiative targeting 195 high-risk lakes, categorized into 4 risk levels. Committee on Disaster Risk Reduction (CoDRR): Brings together States, research institutions, and central agencies for coordinated action. 16th Finance Commission Allocation Plan (FY27–31): Scaling up GLOF mitigation as part of climate-resilient infrastructure.
• NDMA’s National GLOF Programme: A $20 million initiative targeting 195 high-risk lakes, categorized into 4 risk levels.
• Committee on Disaster Risk Reduction (CoDRR): Brings together States, research institutions, and central agencies for coordinated action.
• 16th Finance Commission Allocation Plan (FY27–31): Scaling up GLOF mitigation as part of climate-resilient infrastructure.
• Technological Measures:
• SAR Interferometry for Slope Monitoring: Detects micro-changes in glacier slope stability up to centimetre precision. Electrical Resistivity Tomography (ERT): Identifies presence of ice-cores in moraine dams, a major failure risk. UAV and Bathymetric Surveys: Used to measure lake volume and surrounding terrain vulnerabilities.
• SAR Interferometry for Slope Monitoring: Detects micro-changes in glacier slope stability up to centimetre precision.
• Electrical Resistivity Tomography (ERT): Identifies presence of ice-cores in moraine dams, a major failure risk.
• UAV and Bathymetric Surveys: Used to measure lake volume and surrounding terrain vulnerabilities.
• Community Engagement:
• Involving Local Communities in Expeditions: Ensures cultural sensitivity and local participation in monitoring efforts. Manual Early Warning via ITBP: In areas without AWWS, ITBP acts as sentinels for danger signs. Expeditions to 40 High-Risk Lakes in 2024: multi-institutional fieldwork done in Ladakh, J&K, HP, UK, Sikkim, and Arunachal.
• Involving Local Communities in Expeditions: Ensures cultural sensitivity and local participation in monitoring efforts.
• Manual Early Warning via ITBP: In areas without AWWS, ITBP acts as sentinels for danger signs.
• Expeditions to 40 High-Risk Lakes in 2024: multi-institutional fieldwork done in Ladakh, J&K, HP, UK, Sikkim, and Arunachal.
Conclusion:
Glacial Lake Outburst Floods (GLOFs) are an escalating threat in the Indian Himalayas due to warming temperatures, seismic vulnerability, and unplanned development. India has transitioned from reactive relief to proactive risk reduction, using tech-driven monitoring and local partnerships. Long-term resilience needs sustained investment in early warning systems, cross-border data sharing, and Himalayan climate adaptation.