A massive release of water from a glacial lake in Bhutan has triggered flood alerts in parts of northern West Bengal and Assam. Authorities have moved thousands of people living along vulnerable riverbanks to safer locations. The incident has highlighted the growing threat of Glacial Lake Outburst Floods (GLOFs) in the Himalayan region.
Why in the News?
A sudden breach of Shintaphu Lake in Bhutan released approximately 7.4 million cubic metres of water, raising concerns about flooding in downstream areas of India.
The released water travelled through the Mo (Mofu) River system towards the Sankosh River.
Flood alerts were issued in parts of West Bengal and Assam.
Thousands of residents were evacuated to safer locations.
Schools were converted into relief shelters, and disaster response teams were placed on alert.
The incident highlighted the threat GLOFs pose to communities and infrastructure downstream of Himalayan rivers.
What are Glacial Lake Outburst Floods (GLOFs)?
A Glacial Lake Outburst Flood (GLOF) is the sudden and often catastrophic release of water stored in a glacial lake.
Glacial lakes form when glaciers melt, and water accumulates behind natural barriers made of ice, rocks, and debris.
These natural barriers are known as moraines.
When the natural barrier becomes unstable or collapses, a large volume of water is suddenly released.
The flood moves downstream at high speed and can carry rocks, mud, boulders, trees, and other debris.
Major impacts of GLOFs: Unlike ordinary river floods, GLOFs can release enormous volumes of water within a short period and cause widespread destruction downstream.
Destruction of bridges, roads, and houses.
Damage to dams and hydropower infrastructure.
Loss of human and animal lives.
Damage to agricultural land and settlements.
Disruption of livelihoods and transport networks.
How Does a Glacial Lake Burst?
A glacial lake does not necessarily burst due to rising temperatures alone. Several natural factors can destabilise the barrier holding the water. Once the natural barrier gives way, water rushes downstream at enormous speed, carrying large quantities of rocks, sediment and debris.
1. Avalanches and Landslides
Large volumes of snow, ice, or rocks falling into a lake can displace water.
This can generate powerful waves and cause the lake to overflow its natural barrier.
2. Melting Glaciers
Rising temperatures cause glaciers to retreat.
New glacial lakes are formed, while existing lakes expand.
This increases the volume of water stored behind unstable ice or moraine dams.
3. Heavy Rainfall
Intense rainfall can rapidly increase the water level of a glacial lake.
This puts additional pressure on its natural barriers.
4. Earthquakes
Seismic activity can destabilise moraine dams.
Earthquakes may also trigger landslides into glacial lakes, leading to sudden water displacement.
Why is India Particularly Vulnerable to GLOFs?
India's vulnerability is linked to its geography, geology, climate, and growing infrastructure in the Himalayan region.
1. Large Number of Glaciers and Glacial Lakes
The Indian Himalayan region contains thousands of glaciers and glacial lakes.
Rising temperatures are causing glaciers to retreat.
This leads to the formation of new lakes and the expansion of existing ones.
As a result, the volume of water that may be released during an outburst is increasing.
2. High-Risk Himalayan States and Regions
The threat is particularly significant in:
Sikkim
Himachal Pradesh
Uttarakhand
Arunachal Pradesh
Jammu and Kashmir
Ladakh
3. Findings of a 2020 Study
A study published in Water Resources Research in 2020 assessed 329 glacial lakes in the Indian Himalayas.
Around 22% of these lakes were found to have high or very high hazard levels.
The assessment considered the likelihood of an outburst and its potential downstream impact.
4. Steep Himalayan Terrain
Water released from high-altitude lakes rapidly gains momentum as it flows downhill.
Narrow Himalayan valleys further increase the destructive force of these floods.
Communities located hundreds of kilometres downstream can also be affected.
5. Growing Infrastructure Exposure
Hydropower projects, dams, roads, bridges, and settlements have expanded along Himalayan rivers.
GLOFs carrying large amounts of debris can damage or destroy this infrastructure.
This increases the economic and social impact of such disasters.
6. Impact of Climate Change
Rising temperatures are accelerating glacier retreat.
Changing precipitation patterns can affect the stability and water levels of glacial lakes.
The Intergovernmental Panel on Climate Change (IPCC) has warned that glacier retreat, rising temperatures and changing precipitation patterns can increase glacial lake formation and outburst flood risks in mountain regions.
Can GLOF Disasters Be Prevented?
GLOFs cannot always be prevented. However, their impact can be reduced through scientific monitoring, early-warning systems and better disaster preparedness. Major preventive and mitigation measures include:
Satellite Monitoring: Continuous monitoring of vulnerable glacial lakes to identify changes in their size and water levels.
Early-Warning Systems: Developing systems to provide alerts before floodwaters reach downstream settlements.
Controlled Drainage: Reducing the water level of high-risk lakes through controlled drainage.
Disaster Preparedness: Strengthening evacuation plans and emergency response systems in vulnerable areas.
Climate-Resilient Infrastructure: Developing stronger roads, bridges and hydropower infrastructure to withstand extreme flood events.
India's Efforts to Monitor GLOF Risks
India has strengthened the monitoring and assessment of vulnerable glacial lakes following major disasters in the Himalayan region.
The October 2023 South Lhonak Lake outburst in Sikkim triggered devastating flooding in the Teesta River basin.
The disaster highlighted the need for better monitoring of glacial lakes and stronger early-warning systems.
It also increased attention to the vulnerability of hydropower infrastructure and settlements located along Himalayan rivers.
Transboundary Nature of GLOF Disasters
GLOFs are not limited by international boundaries. A glacial lake may burst in one country, but the resulting flood can affect communities in another country.
The recent Bhutan incident demonstrates the transboundary nature of glacial hazards.
Water released from a lake in Bhutan can threaten downstream areas of India.
This makes cooperation between Himalayan countries important for monitoring, early warnings and disaster management.
Conclusion
The glacial lake outburst in Bhutan highlights the growing climate-related risks facing the Himalayan region. The sudden release of water from high-altitude lakes can cause widespread destruction in downstream areas, even hundreds of kilometres away. For India, the increasing number of glacial lakes, glacier retreat and growing infrastructure exposure make GLOFs a major disaster management challenge. Continuous monitoring, early-warning systems, regional cooperation and climate-resilient infrastructure are essential to reduce the risks and protect vulnerable communities.