Day: November 16, 2016

Lakes are classified depending on how they formed and on the quality of the water (freshwater or saltwater). Only in the saltiest lakes there is no life. Lakes contain 4 times more freshwater than the rivers, but, if they are not continuously supplied with freshwater, they can disappear through desiccation or accumulation of sediments.

A lake helps in preventing flood by regulating the flow of river. During dry seasons, a lake helps to maintain an even flow of the river. Lakes can also be used for generating hydel power.

#1.Tectonic lakes

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• The movements of the Earth’s crust formed the largest lake, the Caspian Sea, and the deepest, Lake Baikal.
• Caspian Sea is located in a depression between the Caucasus Mountains and Central Asia and its surface is still varying, millions of years after its emergence.
• Before the formation of the Caucasus chain, it was connected to the Black Sea.
• Wular lake (Jammu & Kashmir) is the largest freshwater lake in India. It was formed by tectonic activity.

The Great Rift Valley in Africa harbors, from north to south, a chain of lakes like Albert, Edward, Tanganyika and Malawi. The rift penetrates to southwestern Asia, comprising the lake located at the lowest altitude: the Dead Sea, 399 m (1,330 ft) under the sea level.

#2. Volcanic lakes

The most common form is the one filling the caldera of a shut-off volcano. One of the largest lakes of this kind is the Crater Lake, from the crater of Mazama Mountain, Oregon, US. It formed 6,600 years ago, having 10 km (6.2 mi) in diameter, and a depth of 589 m (1.963 ft).

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#3. Ox­bow Lake:

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#4. Glacial Lake

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A lake formed by melting of glacier is called a glacial lake. Most of the lakes in the Himalayan region are glacial lakes.

#5. Lagoon

When the lake is formed by spits and bars in coastal areas, it is called a lagoon. Chilika lake, Pulicat lake, Kolleru lake, etc. are examples of lagoon.

#6. Artificial Lake

The river system of an area is called drainage. The area drained by a single river system is called the drainage basin.

The word watershed is sometimes used interchangeably with drainage basin or catchment. Ridges and hills that separate two watersheds are called the drainage divide.

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Terminology for the study of rivers

• Drainage basin – the area of land drained by a river.
• Catchment area – the area within the drainage basin.
• Watershed – the edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins.
• Source – The beginning or start of a river.
• Confluence – the point at which two rivers or streams join.
• Tributary – a stream or smaller river which joins a larger stream or river.
• Mouth – the point where the river comes to the end, usually when entering a sea.

Drainage Patterns:

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Depending on the slope of land, underlying rock structure and climate of an area, the streams in a drainage basin form certain patterns. Different types of drainage pattern are as follows:

#1. Dendritic Drainage Pattern:

When the river channel follows the slope of the terrain, it develops dendritic pattern. The stream and its tributaries resemble the branches of a tree. Hence, it is called dendritic pattern.

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#2. Trellis Drainage Pattern:

When a river is joined by its tributaries at almost right angles, it develops a trellis pattern. Trellis pattern develops where hard and soft rocks exist parallel to each other.

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#3. Rectangular Drainage Pattern:

When rocks are strongly joined, rectangular pattern develops.

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#4. Radial Drainage Pattern:

• When the streams flow in different directions from a central peak or dome like structure, a radial pattern is developed.
• It is important to note that a combination of different patterns may develop in the same drainage basin.

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A Quick Recap

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