Glacial Lake Outburst Flood (GLOF)
- Glacial lakes are common in the high elevation of glacierized basin. They are formed when glacial ice or moraines or natural depressions impound water.
- There are varieties of such lakes, ranging from melt water ponds on the surface of glacier to large lakes inside valleys dammed by a glacier in the main valley.
- These lakes normally drain their water through seepage in front of the retreating glacier. The moraine creates topographic depression in which the melt water is generally accumulated leading to formation of glacial lake.
- When this lake is watertight, melt waters will accumulate in the basin until seepage or overflow limits the lake level.
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 GLOFs.
- Glacial lakes are typically formed at the foot of a glacier. As glaciers move and flow, they erode the soil and sediment around them, leaving depressions and grooves on the land. Meltwater from the glacier fills up the hole, making a lake.
- Lakes form when meltwater ponds, and this can happen on the ice surface (supraglacial lakes), in front of the ice (proglacial lakes), or even underneath the ice (subglacial lakes).
- Glacier lakes can affect ice flow by reducing friction at the ice-bed interface, encouraging basal sliding.
- They can change the albedo of the ice surface, encouraging more surface melt.
- Proglacial lakes cause calving, which affects mass balance and can decouple mountain glaciers from climate.
- Glacier lakes can be hazardous; moraine and ice dams can fail, causing catastrophic glacier lake outburst floods or jokulhlaups.
Increase in Number of Glacial Lakes
- There has been a rapid increase in the number of glacial lakes due to a retreat in the glaciers caused by warming temperatures (due to global warming), and their potential to cause large scale flooding and destruction.
- Ex. Kedarnath tragedy in 2013 had involved a breach in a large glacial lake.
- According to a study sponsored by the Central Water Commission (CWC), conducted during 2011-15, there are 352, 283 and 1,393 glacial lakes and water bodies in the Indus, Ganga and Brahmaputra basins respectively.
Guidelines on Risk Reduction
- 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.
In 2020, National Disaster Management Authority (NDMA) had issued detailed guidelines on how to reduce and deal with disasters caused by GLOFs/Glacial Bursts. The NDMA guidelines suggest that risk reduction can be done by identifying and mapping potentially dangerous lakes, taking structural measures to prevent their sudden breach, and establishing mechanisms to save lives and property in times of a breach.