Plain is an extensive tract of flat land or a gently undulating terrain without prominent hills or depressions.
Plains are major centres of population concentration in the world.
They are categorised as :
Plains are seldom formed by a single process.
Diastrophic forces have played a dominant role in the evolution of the Great Plains of USA; hence they are called diastrophic plains.
River Eroded Plains: i. Peneplains are regarded as the end-product of normal cycle of erosion (Fluvial cycle of erosion).
Glaciated Plains: i .Plains of the northern part of North America and Western Europe are dominated by the imprints of glacial features. ii. The Ladakh plain of India in the cast of Shyok river is also a glacial-eroded plain.
Wind-Eroded Plain: i. Wind-eroded plains of Sahara (Africa)
Karst Plains: i. Plains of Yugoslavia (Karst region), Chitrakoot (India).
River-Deposited Plains: These include the Piedmont Alluvial Plains formed in the foothill zones (e.g. Bhabar and Terai of Ganga - Yamuna plain), flood plains formed due to deposition of fine sediments in the flood affected areas and Delta plains at the end of the river course (e.g. Ganga-Brahmaputra delta).
Lacustrine Plains: Formed by the filling up of lakes with sediments. Kashmir valley is regarded as a lacustrinc plain.
Lava Plains: Formed of thin sheets of lava coming through fissure erup-tion, e.g. lava plains of Iceland, Argentina, New Zealand, etc.
Wind-Deposited Plains: They include sandy desert plains and loess plains, e.g. the Thar desert plain, Sahara desert, Loess plain of China.
Glacially-Deposited Plains: Plains of North Germany, N.W. Russia, etc. i. Imphal Basin is an example of Lacustrine plain. ii. Uplifted Peneplains are found in the Applachian region (USA) and Chhotanagpur region of Jharkhand (India).