Lakes are bodies of water, either fresh or saline, in natural depressions on the surface of the earth. As we know, the geological agents individually as well as collectively tend to reduce the surface. – of the earth to a continuous and gradual slope. In doing so, sometimes large depressions are formed on the land surface, which when filled up with water are described as lakes. They range in size from a pond to larger ones of hundreds square miles in area.
Lakes are distinguished from swamps since the lakes commonly occur above the mean-sea level and the swamps are low-lying lands where the water-table has just reached the land-surface. Basins are differentiated from lakes as they always have their bottoms below the water-table.
Origin of Lakes
1. By river action:
(a) Lakes may be formed by meandering rivers, which are called as ox-bow, horse-shoe or cut-off lakes.
(b) Rivers may form Lake Basin by erosion at the foot-hill region as a result of the impact of waterfall.
(c) Tributary river by forming bar of sediments across the-main-river may block it to form lake.
(d) Lakes may be found to occur in depressed areas in dried up river beds.
(e) Lakes may be formed by rock-fall or land slide, when the river is blocked by the landslide across its valley.
2. By tectonic movements:
(a) Tectonic depressions relative to the surrounding arc responsible for the largest of the world’s lakes like Caspian Sea, Baikal, Dead Sea, Titicaca etc.
(b) Folding as well as differential faulting like tear faults or thrusts across the pre-existing river valley.
(c) Lakes may also result due to earthquakes.
3. Due to volcanic activities:
(a) Lakes are sometimes formed on the craters and calderas of extinct or dormant volcanoes.
(b) Lava flows forming barriers across pre-existing valleys.
4. Due to glacial actions:
(a) Piling up of morainic matter across their valleys causing the formation of lake.
(b) Kettle-holes left by melting of masses of stagnant ice.
(c) Valleys obstructed by glacial drift.
5. Marine action:
Sometimes sea-waves build bars across the coast or the mouth of a river, thus converting the lake water into small lagoons.
6. Wind action:
Due to extreme grade of deflation hollows are excavated in arid regions to a depth where an adequate supply of ground is available, thus forming Aeolian lakes.
7. By the impact of large meteorites lakes may be formed.
8. Organic activity such as growth of coral reefs leads to the development of lagoons with the emergence of atolls.
9. Ground water action on soluble rocks leads to the collapse of the roof-rock giving rise to lakes, which are known as Poljee.
10. By constructing dams, artificial lake can be created,
Excepting an inconspicuous degree of erosion brought about by lake-water the geological action of lakes are mostly concerned with the deposition of sediments as it becomes a depositional site for the detritus carried by the streams and rivers feeding the lakes.
Lakes in India
(A) Peninsular India
1. Coastal lakes:
(a) Chilika lake, (b) Pulicat lake, and (c) Kayal (Kerala).
2. Lonar lake:
In Buldana area of Maharashtra.
3. Sambar lake:
Small lakes of aeolian origin.
5. Runn of Kutch:
(B) Extra peninsula:
1. Lakes of Kashmir:
Walur, Dal are fresh water lakes while Pangkong, Salt lake, Tsomoriri are saline.
2. The lakes of Kumaon which include Naini Tal, Bhim Tal etc., are thought to be of tectonic origin.