ISRO's satellite images of catchments of Indian Himalayan river basins over the past 40 years have shown a significant expansion of glacial lakes.

The Gepang Gath glacial lake (Indus River Basin) at an elevation of 4,068 m in Himachal Pradesh has witnessed a long-term change, with its size increasing by 178% from 36.49 to 101.30 hectares between 1989 and 2022.
ISRO has flagged that the rate of increase is approximately 1.96 hectares per year.

Risk associated with glacial lakes

Glacial lakes are expanding, which poses significant risks to communities downstream. Glacial Lake Outburst Floods (GLOFs) can occur as a result, which are sudden and severe floods caused by the release of large volumes of meltwater from glacial lakes due to the failure of natural dams made of moraine or ice.
These dam failures can be triggered by various factors, such as avalanches of ice or rock, extreme weather events, and other environmental factors.
In Sikkim, heavy monsoon rainfall and a GLOF caused severe flooding downstream, washing away part of the Teesta 3 dam, damaging parts of Teesta 5, wrecking bridges, and drowning roads.
The cause of the GLOF on Lhonak lake in northwest Sikkim is not yet clear, although the risk had been looming for at least a decade.
The Himalayan Mountains, known as the Third Pole because of their extensive glaciers and snow cover, are highly sensitive to changes in the global climate.
Research conducted worldwide has consistently shown that glaciers across the globe have been experiencing unprecedented rates of retreat and thinning since the eighteenth century's Industrial Revolution. This retreat is leading to the formation of new lakes and enlargement of existing ones.

Glacial Lakes

A glacial lake is a body of water that forms at the foot, on, in, or under a glacier. As global warming continues, glaciers are shrinking, increasing freshwater output to glacial lakes.
While some communities rely on glacial meltwater, the shift towards more meltwater comes with new risks and may not be a reliable long-term water source.

How glacial lakes form

Glaciers move and in doing so, they erode the land beneath them, leaving behind grooves and depressions. The debris they churn up, such as rock and soil, forms ridges called moraines.
When glaciers retreat, they leave behind holes that fill with meltwater, creating glacial lakes. But natural dams made of ice or terminal moraines can also create these lakes. Ice dams form when a glacier surges and blocks a valley or fjord, trapping meltwater.
The moraine-formed dams can be strong and keep sizable lakes intact for years. However, they can also be porous, which allows the lake to slowly drain into nearby rivers.
But too much melting in a short span of time can cause serious issues. If a lake overflows or bursts through natural barriers, flooding can occur downstream and result in damage to roads, infrastructure, and communities.
The eastern Himalayas are at greatest risk for glacial outburst floods, which can be life-threatening downstream.
This area is currently twice as likely to have floods as adjacent regions and threats may triple by 2050 due to warming.