Why in news?

Recently, ISRO released satellite-data-based analysis on expansion of glacial lakes in the catchments of Indian Himalayan River basins.

This is the latest among a series of studies on glacial lakes that have highlighted the risks of glacial lake outburst floods (GLOFs), and their impact on infrastructure and settlements downstream of such lakes.

What’s in today’s article?

• Key highlights of the study by ISRO
• Glacial lakes
• Use of remote-sensing technology to monitor glacial lakes
• Mitigation of risks posed by glacial lakes

Key highlights of the study by ISRO

• The study
  • ISRO’s analysis looked at satellite data archives spanning the past four decades to assess changes in the glaciated environment.
  • Long-term satellite imagery covering the catchments of Indian Himalayan River basins — spread over India, Nepal, Tibet, and Bhutan — is available from 1984 onwards, till 2023.
• Findings
  • ISRO’s data has indicated significant expansion in the size of glacial lakes.
  • Of the 2,431 lakes larger than 10 hectares (identified during 2016-17), 676 glacial lakes had expanded significantly since 1984.
  • ISRO said that 130 of the 676 lakes are situated in India, in the Indus (65), Ganga (7), and Brahmaputra (58) river basins.
  • These lakes have expanded as glaciers are retreating at an ever-faster rate due to global warming.

Glacial lakes

• About
  • Glacial lakes are bodies of water that form in depressions or basins created by the erosive action of glaciers.
  • These lakes are typically found in regions where glaciers have previously existed or are currently present.
  • Glacial lakes vary in size and shape, ranging from small ponds to large, deep bodies of water.
  • ISRO categorised glacial lakes into four broad categories based on how they were formed — moraine-dammed, ice-dammed, erosion-based, and ‘others’.
  • Glacial lakes are crucial sources of freshwater for rivers.
  • However, they also pose significant risks, specifically of Glacial Lake Outburst Floods (GLOFs).
    • GLOFs occur when glacial lakes release large volumes of meltwater due to the failure of natural dams, resulting in sudden and severe flooding downstream.
• Formation
  • Glacial Erosion:
    • Glaciers are massive bodies of ice that move slowly over the landscape, eroding and shaping the underlying bedrock through processes such as abrasion and plucking.
    • As glaciers advance, they carve out deep valleys and basins in the landscape.
  • Deposition of Glacial Moraines
    • As glaciers move, they carry vast amounts of sediment and debris, including rocks, gravel, and sand.
    • When glaciers retreat or melt, they deposit this material at their edges, forming features called moraines.
    • Moraines can act as natural dams, blocking the flow of water and creating depressions where glacial lakes can form.
  • Melting Ice
    • As temperatures rise or glaciers retreat, the ice within the glacier melts, filling the depressions created by glacial erosion with water.
    • This water collects in the basins, forming glacial lakes.
  • Terminal Moraine Formation
    • In some cases, glaciers deposit large ridges of sediment and debris at their terminus, creating natural dams that impound water and form glacial lakes behind them. These lakes are called terminal moraine lakes.

Use of remote-sensing technology to monitor glacial lakes

• The monitoring of glacial lakes and their expansion in the Himalayan region is challenging due to the rugged terrain.
• This is where satellite remote-sensing technology proves to be an excellent tool.
• Analyzing changes in glacial lakes using satellite data helps us understand how these lakes are changing over time.
• This information is crucial for figuring out how they affect the environment and for creating plans to manage the risks of glacial lake outburst floods and adapt to climate change in areas with glaciers.

Mitigation of risks posed by glacial lakes

• As per one study, lowering of the lake levels by 10 to 30 m significantly reduces the impacts on downward towns.
  • Although it does not completely eliminate the risks posed by a GLOM event.
• One way to syphon off lake water is by using long High-Density Polyethylene (HDPE) pipes.
• In 2016, members of the Sikkim State Disaster Management Authority used this method to reduce water levels in Sikkim’s South Lhonak Lake.