Plains are areas with a maximum of gentle slope and minimum of local relief. Plains also be differentiated according to their location:
- Coastal Plains are found near continental shorelines and have emerged from beneath the sea.
- Interior Plains are found in continental interiors, away from the oceans.
- Lacustrine Plains are extremely flat former lake beds.
The surface material of plains also varies a great deal over the world. Some have very fertile soils, and others are ice-covered, rocky, sandy or swampy.
Some plains are formed by erosion. In humid areas, the effects of weathering and erosion over long periods of time gradually wear down the elevations and rough surfaces of hills to form gently rolling plains.
Classification of Plains
On the basis of their mode of formation, plains are classified into the following types:
- Structural Plains
- Erosional Plains
- Depositional Plains
These plains are mainly formed by the uplift of a part of the sea-floor or continental shelf. These are located on the borders of almost all the major continents. The south eastern plain of the United States formed by the uplift of a part of the Gulf of Mexico is an example of this type of plain. The structural plains may also be formed by the subsidence of areas. One such plain is the central low-lands of Australia.
These plains are formed by the continuous and a long time erosion of all sorts of upland. The surface of such plains is hardly smooth. These are therefore also called peneplains which means almost a plain. The Canadian shield and the West Siberian plain are examples of erosional plains.
Fragments of soil, regolith, and bedrock that are removed from the parent rock mass are transported and deposited elsewhere to make on entirely different set of surface features - the depositional landforms.
When plains are formed by river deposits, they are called riverine or alluvial plains. The Indo Gangetic plain of the Indian sub-continent, the Hwang-Ho Plain of North China, the Lombardy Plain of the Po river in Italy and the Ganga-Brahmaputra Delta Plain in Bangladesh are examples of alluvial plains.
The deposition of sediments in a lake gives rise to a lacustrine plain or a lake plain. The Valley of Kashmir and that of Manipur are examples of two most prominent lacustrine plains in India.
When plains are formed by glacial deposits they are called glacial or drift plains. Plains of Canada and North-Western Europe are examples of glacial plains.
When wind is the major agent of deposition, they are called loess plains. Loess plains of North-Western China are formed by the deposits of loessair-borne fine dust particles.