Glacial Lakes/Water Bodies in Himalayan Region
Glacial lakes are common in the high elevation of glacierised basin. They are formed when glacial ice or moraines or natural depressions impound water. There are varieties of such lakes, ranging from melt water ponds on the surface of glacier to large lakes in side valleys dammed by a glacier in the main valley. These lakes normally drain their water through seepage in front of the retreating glacier. The moraine creates topographic depression in which the melt water is generally accumulated leading to formation of glacial lake. When this lake is watertight, melt waters will accumulate in the basin until seepage or overflow limits the lake level.
Such moraine-dammed lakes appear to be the most common type of glacial lakes. The impoundment of the melt may sometimes be unstable, leading to sudden release of large quantities of stored water. Failure of these ice or moraine dams leading to disastrous destruction events has been documented throughout the world. Flash floods caused by the outburst of glacial lakes, called as Glacial Lake Outburst Flood (GLOF), are well known in Himalaya where such lakes had often been formed by landslides. GLOFs have immense potential of flooding in downstream areas, causing disastrous consequences due to release of large volumes of water in very short interval of time. Most often, the consequences arising out of such situations are highly unpredictable primarily due to lack of availability of sufficient data regarding rainfall intensity, location of landslide, impounded volume and area and physical conditions of lakes/ water bodies. Therefore, Glacial Lakes and Water Bodies in Himalayan Region need to be closely monitored.