What are Glacial Lakes?

About Glacial Lakes:

• A glacial lake is a body of water that originates from a glacier.
• It typically forms at the foot of a glacier, but may form on, in, or under it. 
• ISRO categorised glacial lakes into four broad categories based on how they were formed — moraine-dammed, ice-dammed, erosion-based, and ‘others’.
• How do glacial lakes form?
  • As glaciers move, they erode the terrain under them, leaving depressions and grooves on the land. 
  • When they churn up rock and soil, they etch ridges of debris known as moraines.
  • Most glacial lakes form when a glacier retreats and meltwater fills the hole left behind. 
  • However, natural dams, formed out of ice and terminal moraines, can also form glacial lakes.
  • An ice dam forms when a surging glacier, which can move up to 100 times faster than an average glacier, may dam up meltwater as it closes off a valley or fjord and prevents it from draining.
  • Dams formed by moraines can be dense and stable, holding sizable lakes behind them for years. 
  • They can also be leaky, allowing the lake to drain slowly into nearby rivers.
• 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.