The National Disaster Management Authority (NDMA) has finalised a list of 189 “high-risk” glacial lakes for mitigation measures to reduce the risk emanating from them.
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.
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