Glacial Lake Outburst Floods (GLOF)

What is the News?

Parts of Uttarakhand witnessed massive flooding due to Glacial Lake outburst.

 What is Glacial Lake Outburst Floods(GLOF)?

• It is a type of outburst flood. It occurs when water dammed by a glacier is released. In other words, it’s an outburst that happens when a dam containing a glacial lake fails.

Note: An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier is called a jökulhlaup.

How does GLOF happen?

• Retreating glaciers, like several in the Himalayas, usually result in the formation of lakes at their tips, called proglacial lakes. It is often bound only by sediments and boulders.
• If the boundaries of these lakes are breached, it can lead to large amounts of water rushing down to nearby streams and rivers. It gathers momentum on the way by picking up sediments, rocks, and other material, and resulting in flooding downstream.

Features of GLOF: The three main features are:

• They involve sudden (and sometimes cyclic) releases of water.
• They tend to be rapid events, lasting hours to days.
• Furthermore, they result in large downstream river discharges (which often increase by an order of magnitude).

Causes behind GLOFs

The boundaries of glacial lakes breach due to multiple reasons. Like,

1. A buildup of water pressure or structural weakness of boundary due to an increase in the flow of water.
2. An earthquake (Tectonic) or cryoseism (non-tectonic seismic event of the glacial cryosphere) can also cause GLOF. During this, the boundary of the glacial lake will collapse suddenly and release the water in the glacial lake.
3. An avalanche of rock or heavy snow: During this, the water in the glacial lake might be displaced by the avalanche.
4. Volcanic eruptions under the ice can also cause GLOF. These volcanic eruptions might displace the boundary or increase the pressure on glacial lake or both.
5. Heavy rainfall/melting of snow: This can lead to massive displacement of water in a glacial lake.
6. Long-term dam degradation can also induce GLOF.
7. Other reasons such as the collapse of an adjacent glacial lake, etc.

What are Glaciers?

• Glaciers are made up of fallen snow. It compresses into large, thickened ice masses over a period of time. They are formed when snow remains in one location long enough to transform into ice.
• Where are Glaciers found? Glaciers are found on every continent except Australia. Some are hundreds of thousands of years old. A large cluster of glaciers are in the Himalayas, which are part of India’s long northern border.

Source: The Hindu