GLACIAL BURST FLOODS

GLACIAL BURST FLOODS

Subject : Geography

Context : Uttarakhand witnessed loss of lives, disappearances and devastation of property due to a glacial burst at Joshimath in Uttarakhand’sChamoli district which triggered floods that destroyed two hydropower projects near the Naina Devi National Park.

Concept :

Glacial Lake Outburst Flood (GLOF):

• A GLOF refers to the flooding that occurs when the water dammed by a glacier or a moraine (accumulations of dirt and rocks fallen onto the glacier surface) is released suddenly.
• When glaciers melt, the water in glacial lakes accumulates behind loose, natural “glacial/moraine dams” made of ice, sand, pebbles and ice residue.
• Unlike earthen dams, the weak structure of the moraine dam leads to the abrupt breach of the dam on top of the glacial lake which could cause flash floods in the downstream areas.
• According to NDMA, glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs.

Glacial Lakes:

• Glacial lakes are typically formed at the foot of a glacier.
• As glaciers move and flow, they erode the soil and sediment around them, leaving depressions and grooves on the land. Meltwater from the glacier fills up the hole, making a lake.

Types:

• Lakes form when meltwater ponds, and this can happen on the ice surface (supraglacial lakes), in front of the ice (proglacial lakes), or even underneath the ice (subglacial lakes).

Impact:

• Glacier lakes can affect ice flow by reducing friction at the ice-bed interface, encouraging basal sliding.
• They can change the albedo of the ice surface, encouraging more surface melt.
• Proglacial lakes cause calving, which affects mass balance and can decouple mountain glaciers from climate.
• Glacier lakes can be hazardous; moraine and ice dams can fail, causing catastrophic glacier lake outburst floods or jokulhlaups.