Write a brief note on Long Profile Lakes

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Lakes represent another form of irregularity in the long profile of rivers in their early stages. The Himalayan Rivers have practically no lakes along their courses. This indicates the relative maturity of landscape in the region. The only notable exceptions are the lakes of Kashmir valley in the long-profile of the Jhelum. But here too the lakes are not due to structural discordance but mainly due to the tectonic depression which the vale is. No doubt, the Baramula gorge is a point of structural discordance and with the passage of time as the threshold at the gorge is lowered the long-profile may undergo straightening and draining out of the lakes in the valley. The only other considerable lake in the Himalaya is Nainital in the long-profile of a small river. This is believed to be a solution lake in a limestone region of Nainital district.

Ephemeral lakes may be formed in the course of rivers by landslide or avalanche damming water upstream of such barrier. Long-profile lakes are mostly confined to the neighborhood of source region, e.g., Mansarowar and Rakas lakes in the headstream region of the Sutlej or Lake Albert in the source region of the Nile or the Great Slave Lake in the source region of the Mackenzie or Lake Ontario in the source region of St. Lawrence. Some of them are glacial lakes due to glacial erosion of depressions or obstruction caused by glacial deposits or alluvial deposits from side tributaries. As such, they may generally be unrelated to the present river morphology and process.

Wherever the long-profile lakes exist, they are mostly confined to the mountain section of the course where the morphology is relatively young although its geological origin may be old.

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After the lakes have appeared in the long-profile of rivers, they generally begin to die out because of different reasons. These include the incoming of sediments and building of fans or deltas on the upstream side, growth of , organisms, draining out due to the down cutting or straightening of gradients at the downstream side of the lake, wearing away of temporary barriers like landslides.

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