Our Changing Earth — Social Science STD 7 — Question

Work of a River:

• Running water in the river erodes the landscape.
• When the river tumbles at steep angle over very hard rocks or down a steep valley side, it forms a waterfall.
• When the river enters the plain it twists, turns and forms large bends. These bends are known as meanders.

Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer.

• In due course of time the meander loop cuts-off from the river and forms a cut-off lake.
• It is called an ox-bow lake.
• At times the river overflows its banks.
• This leads to the flooding of the neighbouring areas.
• The flood water deposits layers of fine soil and other material.
• They are called sediments, along its banks.
• This leads to the formation of a flat fertile land called a flood plain.
• The raised banks are called levees.

As the river approaches the sea, the speed of the running water decreases.

• The river begins to break up into a number of streams. They are called distributaries.
• Now the river becomes so slow that it begins to deposit its load.
• Each distributary forms its own mouth.
• The collection of sediments from all the mouths forms a delta, the triangular shaped land mass.