Lakes

A lake is a large inland body of water which is surrounded by land and is not connected with sea except by rivers. Lakes are formed in a number of ways of which erosional and depositional works of agents of change like rivers, glaciers, wind and waves is important. Great Lakes of North America have been formed by the erosional work of glaciers. In several parts of the world ox-low lakes have been formed by meandering rivers. Playa lakes are formed in deserts where rain water was into local depressions. They are generally seasonal and their size shrinks in dry season. Lake Chad in Africa and Sambhar lake in Rajasthan are such lakes.

Lagoons are formed along the sea coast due to the action of sea waves. Chilka lake in Orissa and Pulicot lake in Andhra Pradesh are important lagoons of India. Some lakes like Baikal Lake of Russia and a large number of lakes in Africa occupy structural depressions caused by faulting etc. When rain water accumulates in craters caused by volcanoes, crater lakes are formed. Sometimes craters are also formed by impact of meteors and water accumulates in such craters in the form of lakes. Some lakes in Siberia and Lake Lonar in Maharashtra have been formed in this way. Some of the large lakes such as the Caspian Sea are the remnants of ancient ocean and sea areas.

Depending on the nature of water, two types of lakes are recognised. They are

• fresh water lakes and
• salt water lakes.

Lakes which receive a continuous flow of fresh water through rivers or melting of glaciers are fresh water lakes. The Great Lakes of North America and Wular lake in Kashmir are examples of fresh water lakes. In desert areas, there is less supply of fresh water and the rate of evaporation is very high. Under these conditions, salt lakes are formed. The Great S alt Lake of the U.S.A, Lake Van of Turkey, the Dead Sea and some lake Sambhar salt lane in Rajasthan are examples of salt lakes. Salt lakes usually dry up in dry hot season and a crust of hard mud and salt is left behind. This type of areas are known as alkali flats. Such lakes are formed in the desert of south-west Asia.

Some of the lakes have been made by the activities of man and are termed as man made lakes. Generally such lakes are formed as water reservoirs behind dams constructed across the rivers. Gobind Sagar Lake behind Bhakhra Dam on Satluj as well as Gandhi Sagar and Jawahar Sagar lakes under Chambal Valley Project are some of the examples of man-made lakes. Some of the important lakes with an area of over ten thousand sq km are listed in the following table.

Important Lakes of the world (area above 10,000 sq. km.)