Rising Glacial Lakes: Impacts of Glacial Retreat and Global Warming

Rising Glacial Lakes: Impacts of Glacial Retreat and Global Warming

Sub: Geo

Sec: Climatology

Why in News

In recent years, glacial retreat due to global warming has led to a significant increase in the formation and expansion of glacial lakes. The situation has raised concerns about the stability of these lakes and the risks of glacial lake outburst floods (GLOFs), particularly in regions like the Himalayas where communities and infrastructure are vulnerable to such events.

What Are Glaciers?

Glaciers are massive, dense ice formations found on mountains, moving due to gravity and their own weight.

As glaciers move, they erode the underlying land, breaking rocks into a material known as moraine. This moraine includes particles of various sizes, from large boulders to fine “rock flour.”

When snow falls and accumulates new layers over time, it gets compressed into large, thick masses of ice, forming glaciers.

The upper part of the glacier — called the accumulation zone — receives precipitation in the form of snow, which accumulates over time.

But in the lower part of the glacier — called the ablation zone — there is more melting of the snow and ice than accumulation.

The balance between the accumulated and melted snow is known as the glacier mass balance, which determines the health of the glacier.

Glaciers are crucial for downstream communities as they provide drinking water, or water for irrigation.

Glaciers also regulate river flow and counter global warming.

Formation of Glacial Lakes:

Retreating Glaciers: When glaciers melt, they leave behind large depressions that fill with meltwater, forming glacial lakes.

Natural Dam Formation: The moraine material left by the glacier often acts as a natural dam, allowing the lake to form.

Buffer Role: These lakes act as natural reservoirs, regulating water flow from melting glaciers. However, their formation also brings risks, especially to downstream communities.

Distinctive Blue Color: Glacial lakes often have a striking blue or turquoise colour due to light scattering by ultra-fine rock flour particles suspended in the water.

Global warming has accelerated glacial melting, leading to the expansion of glacial lakes.

Increased GLOF Risks: As glacial lakes grow, the natural moraine barriers holding them can become unstable, leading to potential GLOFs.

Examples in the Himalayas:

Gurudongmar Lake (Northern Sikkim): At 5,430 meters above sea level (msl), it is one of the highest lakes globally and feeds into the Teesta River.

Pangong Tso (Ladakh): A 134-km-long chain of lakes in the disputed region between India and China.

Samiti Lake (Sikkim): Located at 4,300 msl, it lies on the route to Kanchenjunga, one of the highest peaks in the world.

South Lhonak: The South Lhonak Lake appeared in satellite imagery in 1962. It expanded from 17 hectares in 1977 to 167 hectares by 2023. In 2023, heavy rains caused the lake’s moraine dam to breach, raising the Teesta River’s water level by six meters, resulting in the collapse of the Teesta III dam and widespread damage.

What are GLOFs?

GLOFs are disaster events caused by the abrupt discharge of water from glacial lakes — large bodies of water that sit in front of, on top of, or beneath a melting glacier.

As a glacier withdraws, it leaves behind a depression that gets filled with meltwater, thereby forming a lake.

The more the glacier recedes, the bigger and more dangerous the lake becomes.

Such lakes are mostly dammed by unstable ice or sediment composed of loose rock and debris.

In case the boundary around them breaks, huge amounts of water rush down the side of the mountains, which could cause flooding in the downstream areas, which is referred to as a GLOF event.

Reasons for GLOFs:

GLOFs can be triggered by various reasons, including glacial calving, where sizable ice chunks detach from the glacier into the lake, inducing sudden water displacement. 

Incidents such as avalanches or landslides can also impact the stability of the boundary around a glacial lake, leading to its failure, and the rapid discharge of water.

GLOFs can unleash large volumes of water, sediment, and debris downstream with formidable force and velocity. 

Rising surface temperatures across the globe, including India, have increased the risk of GLOFs.

The floodwaters can submerge valleys, obliterate infrastructure such as roads, bridges, and buildings, and result in significant loss of life and livelihoods.