Competitive Exams: Plains geography notes on origin and depositional

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Are flat areas with low height;

  • An extensive tract without prominent hills and depressions

  • Some plains are only a few mts. above the sea level, examples argisouth deltaic plains qfBangladesh. Some are quite high, examples are-the eastern Missisippi plain (450 m high), even higher than the Piedmont plateau;

  • Thus, it should be mentioned that the plains maybe above the or below the sea levels but not higher than the surrounding regions;

  • The slope should be quite gentle, the average fall of the slope should be 4 mts. and in extreme cases, not more than 50mts.

Mode of Origin

Because of endogenetic factors and diastrophic movements, i.e., structural plains. Examples are- Great plains of USA, Gulf coastal plain, Atlantic plain, Russian platform -also called epicontinental form; Great plains (USA) are bordered by Rockies in the west, Central lowland province in the east, Mississippi Missouri plateau and by Reogrande river in south and plains of Canada in the north.

Atlantic coastal plains: It startsfrom Newyork to Gulf of Mexico.Its average width is 480 kms. and is of Miocene and Pliocene. The average gradient is 10 ft/mile, the other is Coromandel and Northern Circar coastal plains, formed due to mile subsidence and consequent sedimentation. Erosional plains: Due to erosion (it is formed). It is of four types:

  1. Peneplains: It happens due to weathering and rivers. It is characterized by convex, concave residual hills, called the 'monadnocks'. Examples are-Chambal, Swaranghati, Mississippi, South Africa.

  2. Glacial plains: Glaciers transform highland areas through their slow but continued erosive works into lowlands. Examples are- Sweden, Finland, Ladakh, Imphal basin. (Manipur hills), Canada.

  3. Wind-eroded plains: Reg, Serir and Hamada (Sahara), Aravalli (arid .plains) near Jaisalmer.

  4. Karst plains: It is composed of limestones. Examples are-Yugoslavia's and Mexico's Karst plains.

Depositional plains

It is of five types:

1.Alluvial plains: Examples are- Mississippi delta, Lomb-ardi plains (Italy) formed by Po river, Yangtze plain (China), Indus plain (Ganga), USA plain (Sacramento), Russia (Samarkand), South America (Chile) plain, Amazon plain, Salween and Mekong plains. [It is formed due to the rivers]. Delta plain: Ganga delta is the largest delta of the world (llakh 29 thousand, the tributaries of delta are called distributaries.

2.Glacial plains: These are of two types:

  1. True glacial plains: These are formed of pure glacial materials;

  2. Outwash plains: These are formed due to deposition of materials after the ablation of glaciers and ice sheets. Glacial plains are divided into three parts on the basis of structure and composition: -Till: Finer or coarser materials; Eskars and Drumlins; -Morainic: finer glacial materials;

  3. Outwash: Admixture of sands, gravels, silts and clays. Examples are- West Germany, north-west Russia, north-west USA, central Canada.

3.Lacustrine plains: When lakes are filled with sediments; examples are- Kashmir valley, Imphal basin, Hungary plain, Great lakes (North America)

4. Loesses plains: It is formed due to air transportation of the sand; it is an unstratified, homogeneous, finegrained.

Examples are- Loesses of China, Europe, USSR, lower Missisippi (USA), Rhine valley (Alsace), southern Netherlands,

5.Lava plains: Examples are-France, USA, Iceland, Argentina, NewZealand. These are economically very important because black soils are formed due to weathering of lavas. These black soils are also called 'Regur' soils are good for growing cotton.