Plains are large stretches of flat land and are generally not more than 200 metres above mean sea level. Some plains are extremely level, others may be slightly rolling and rugged. Most of the plains are formed by rivers and their tributaries. As these are the best fit for cultivation, the concentration of people also occurs in vast extent.
» Plains may be grouped into "three" based on their mode of formation. They are
(1) Structural plains
(2) Depositional plains
(3) Erosional plains
1. Structural Plains: These plains are formed by horizontally bedded rocks, relatively undisturbed by crustal movements of the Earth.
e.g.: The great plains of U.S.A. & Central lowlands of Australia.
2. Depositional plains: These plains are formed by the deposition of materials brought by various agents of transportation and due to deposition by large rivers.
* Alluvial plains are formed as a result of large quantities of alluvium being brought down by the rivers due to erosion and are best fit for cultivation.
e.g.: The plain of Hwang Ho in China supports a wide range of crops.
* Glacial plains occured due to the drop down of boulders clay by the glaciers and ice sheets.
e.g.: Mid − West of U.S.A. & East Anglia in England.
3. Erosional plains: The plains which are occured due to the agents of Erosion are named as Erosional plains. Rain, rivers, ice and wind help to smooth out the irregularities of the Earth's surface.
e.g.: Amazon plain of Brazil, Indus plain... etc.
Uses of Plains
* Plains are most useful areas for human habitation.
* Plains land is suitable for building houses and so large number of people found in these areas.
* Plains provide best − fit land for cultivation, hence wide − variety of plantation can be done.
* In India, Indo − Gangetic plains are the most densely populated regions of the country.