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Glacial Lake Outburst Floods (GLOF)

2023 OCT 10

Mains   > Disaster Management   >   Disaster mitigation   >   Floods


  • Recently, flash floods occurred in north Sikkim after the South Lhonak Lake (a glacial lake situated in the state’s northwest at 17,000 feet) burst due to incessant rains.
  • For years, numerous studies highlighted the lake’s rapidly growing size and marked it as susceptible to glacial lake outburst flood (GLOF).
  • The Teesta basin in the Sikkim Himalaya is home to several glacial lakes in the high-altitude, glacier-covered terrain. Among them, South Lhonak Lake stands out as one of the largest and fastest-growing.


  • The voluminous outflow due to GLOF has destroyed the Chungthang dam, which is critical to the Teesta 3 hydropower project, and rendered several hydropower projects along the river dysfunctional.
  • There is also a suggestion that a series of earthquakes in Nepal in the first week of October 2023 (whose tremors were even felt in the Delhi National Capital Region) might have played a role in the GLOF in Sikkim.
  • With the rising global temperatures, glaciers in the Sikkim Himalaya have been melting rapidly, giving rise to many glacier lakes and expanding the already existing ones in the region.
  • According to the Sikkim State Disaster Management Authority, there are currently more than 300 glacial lakes in the Sikkim Himalaya; out of these, 10 have been identified as vulnerable to outburst floods.



  • A Glacial Lake Outburst Floods (GLOF) is a type of flood occurring when water dammed by a glacier or a moraine is released suddenly.
  • When glaciers melt, the water in these glacial lakes accumulates behind loose naturally formed 'glacial/moraine dams' made of ice, sand, pebbles and ice residue.
  • Unlike earthen dams, the weak structure of the moraine dam leads to the abrupt failure of moraine dam on top of the glacial lake, which holds large volume of water.
  • A catastrophic failure of the moraine dam can release the water over periods of minutes to days causing extreme downstream flooding.
  • Glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of Glacial Lake Outburst Floods (GLOFs).


  • Earthquake:
    • An earthquake (Tectonic) or cryoseism (non-tectonic seismic event of the glacial cryosphere) can also cause GLOF.
    • During this, the boundary of the glacial lake will collapse suddenly and release the water in the glacial lake.
  • An avalanche of rock or heavy snow:
    • During this, the water in the glacial lake might be displaced by the avalanche.
  • Volcanic eruptions
    • Volcanic eruptions under the ice can also cause GLOF.
    • These volcanic eruptions might displace the boundary or increase the pressure on glacial lake or both.
  • Increase in flow of water:
    • A buildup of water pressure or structural weakness of boundary due to an increase in the flow of water.
  • Heavy rainfall/melting of snow:
    • This can lead to massive displacement of water in a glacial lake.
  • Long-term dam degradation can also induce GLOF.


  • Identifying potentially dangerous lakes:
    • Potentially dangerous lakes can be identified based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam and surroundings, and other physical conditions.
  • Use of technology:
    • Promoting use of Synthetic-Aperture Radar imagery (a form of radar that is used to create two-dimensional images) to automatically detect changes in water bodies, including new lake formations, during the monsoon months.
    • Methods and protocols could also be developed to allow remote monitoring of lake bodies from space.
  • Channeling potential floods:
    • To manage lakes structurally, the NDMA recommends reducing the volume of water with methods such as controlled breaching, pumping or siphoning out water, and making a tunnel through the moraine barrier or under an ice dam.
  • Uniform codes for construction activity:
    • Developing a broad framework for infrastructure development, construction and excavation in vulnerable zones.
    • There is a need to accept procedures for land use planning in the GLOF prone areas.
  • Enhancing early warning systems (EWS):
    • The number of implemented and operational GLOF EWS is very small, even at the global scale.
    • In the Himalayan region, there are at three reported instances (two in Nepal and one in China) of implementation of sensor- and monitoring-based technical systems for GLOF early warning.
  • Training local manpower:
    • Apart from pressing specialised forces such as National Disaster Response Force (NDRF), ITBP and the Army, NDMA has emphasised the need for trained local manpower.
    • It has been observed that over 80% of search and rescue is carried out by the local community before the intervention of the state machinery and specialised search and rescue teams.
    • The local teams could also assist in planning and setting up emergency shelters, distributing relief packages, identifying missing people, and addressing the needs for food, healthcare, water supply etc.
  • Comprehensive alarm systems:
    • Besides classical alarming infrastructure consisting of acoustic alarms by sirens, modern communication technology using cell and smartphones can complement or even replace traditional alarming infrastructure.
  • Awareness generation:
    • NDMA emphasized the need for psychological counselling of victims
    • Dissemination of accurate information through press conferences and mass media.


  • Short Term:
    • Formation of Specialized Committee under Ministry of Jal Shakti:
      • The committee should involving expert agencies dealing with research and development on Glacial, Landslide and Flood Hazards
      • It aims to formulate specific land use zoning, development control, building construction regulations etc.
    • Hiring group of expert agencies to identify susceptible sites through Remote Sensing and GIS
    • Development of Early Warning System (EWS) based on Ground Instrument, Water level sensors
    • Set up a regular monitoring system using remote sensing satellites and GIS.
  • Long Term:
    • Use of technology:
      • Use of web-based and app-based dissemination tools for the preparation of maps for common use not only by the administrators but also by the community, tourists etc.
    • Awareness programme on GLOF hazard
      • NDMA should identify not-for-profit organisations to undertake the awareness building activities
      • Use of traditional art forms/ traditional knowledge is necessary to document and disseminate old traditional best practices available in mountain regions of India through community participation in trainings
    • National Data Centre on GLOF:
      • It would integrate various data sources, a geo-portal to address the data needs and thus, enable an effective response


  • Institutional Mechanisms
    • The National Disaster Response Force (NDRF)/SDRF mandated by the DM Act, 2005, will address, in close collaboration with all other field level agencies, all concerns regarding the response to the threat of GLOF disaster
  • Centre for Glacial Research, Studies & Management (CGRSM)
    • This initiative will help in ensuring a wider view of glacial studies as a component of the environment/climate change
  • Comprehensive and Pilot National GLOF Mitigation Projects
    • It aims for assessing risk of GLOFs, enhancing the promptness and efficacy of response to impeding threats of GLOF, geological and geotechnical investigations of GLOF etc.


  • Assessment and reduction of risk:
    • Assessment of the risk and vulnerabilities associated with GLOF disasters and reduction in the degree of the risk, severity or consequences of GLOF
  • Greater coordination:
    • Unlike an earthquake, which is relatively sudden, GLOF events can be anticipated, as we could monitor changes in the size of lakes. But this requires greater coordination.
    • So early warning systems require a coordinated approach, such as multiple agencies promptly sharing satellite images (that are trained towards the Himalayas) and a network of sensors to provide adequate warning.
  • Greater care while planning infrastructure projects:
    • For instance, while the Teesta River is a source of hydropower generation for several power projects, the risk of GLOF-like events requires greater care in planning and executing dams and other infrastructure projects, which account for the huge amount of water that can potentially gush through the mountains.
  • Capacity building:
    • Establishment of monitoring and early warning systems for susceptible glacial lakes.
    • Spreading awareness with a stress on preparedness and providing advice and training to the agencies involved in the management of GLOF.
  • Efforts required post-disaster:
    • Ensuring that proper arrangements are made for organizing rescue, relief and rehabilitation works.
    • Improving the quality and increasing the speed of rehabilitation and reconstruction process.


Q. Explain the features of Glacial Lake Outburst Flood (GLOF). Also analyze India preparedness towards mitigating the risk of GLOFs?