In August 2014, a glacial lake outburst flood (GLOF) hit the village of Gya in Ladakh, destroying houses, fields and bridges. Researchers now have mapped the evolution of Gya glacial lake and note the cause of the flood.

What is glacial lake outburst flood?

• A GLOF is a type of outburst flood that occurs when the dam containing a glacial lake fails.
• An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a Jökulhlaup.
• The dam can consist of glacier ice or a terminal moraine.
• Failure can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake, volcanic eruptions under the ice, or glacier collapses into it.

 How did it happen in Ladakh?

• It was not a spillover but rather a tunnelling of drainage process that caused GLOF in Gya lake.
• Imagine a bucket full of water. It can overflow when you drop a stone, or the water can drain if there is a hole under the bucket.
• Similarly, here the flooding did not happen due to the spillovers due to an avalanche or landslide, rather there was a thawing of the ice cores in the moraine.

Back2Basics: Glacial Landforms

Glacial landforms are landforms created by the action of glacier movements.

As the glaciers expand, due to their accumulating weight of snow and ice they crush and abrade and scour surfaces such as rocks and bedrock.  The resulting erosional landforms include striations, cirques, glacial horns, arêtes, trim lines, U-shaped valleys, over-deepening and hanging valleys.

• Cirque: Starting location for mountain glaciers
• Cirque stairway: a sequence of cirques
• U-shaped, or trough, valley: U-shaped valleys are created by mountain glaciers. When filled with ocean water so as to create anthe glacial action erodes through, a spillway (or col) forms
• Valley step: an abrupt change in the longitudinal slope of a glacial valley

When the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms.  Examples include glacial moraines, eskers, and kames. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers.

• Esker: Built-up bed of a subglacial stream
• Kame: Irregularly shaped mound
• Moraine: Feature can be terminal (at the end of a glacier), lateral (along the sides of a glacier), or medial (formed by the merger of lateral moraines from contributary glaciers)
• Outwash fan: Braided stream flowing from the front end of a glacier

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