1. Depositional Plains: They are formed by the deposition of transported materials brought by various agents. They can be sub-divided as follows:
Alluvial Plains: These are formed by the gradual accumulation of silt brought by rivers from the upper course to the lower course. flood plains and deltaic plains are in this sub-group. Some examples of alluvial plains are the flood plains of Rivers Niger, Nile and Mississippi and their deltas.
Glacial Plains: They are formed mostly by deposition of sediment brought by ice sheets. Example of Glacial plains are outwash and till plains.
Lacustrine Plains: A lacustrine plain is the bed of a former lake, filled in by sediment deposited by inflowing rivers. Example of lacustrine plains; the lacustrine plains left behind by Lake Agassiz in Canada.
Coastal Plains: These are due to the deposition of marine and stream sediment on sea beaches. Example of Coastal Plains is the coastal plain around Lagos in Nigeria.
Lava Plains: They are formed through the filling up of valleys by flowing lava. Example of lava plains is the basatic lava plain in New Mexico.
Sand Dune Plains: Such plains are in deserts, semi-deserts or the sahelian zone of West Africa where these is sparse vegetation and plenty of sand.
Flood Plains: These are areas of lowland adjacent to a river, built up by deposits of alluvium. Each time a river floods its banks, it spreads a layer of silt on the adjacent plains. The level of the plains rise with each layer that is deposited. Flood plains are fertile and are usually intensively cultivated. Examples of flood plains are the flood plains of the Indus, the Ganges, the Tigris and the Nile.
2. Erosional Plains
Pedi-plains: These are formed by the prolonged action of agents of denudation.
Pene-Plains: These are almost level plains formed by the wearing down of mountains and plateaux by agents of denudation. The Hudson Bay lowland is a good example of a peneplain.
3. Marine Plains
Marine plains are formed from residual marine deposits which are produced after a fall in the level of the sea. Such plains are features of coastal lowlands of emergence as we have in the north coast of the Gulf of Mexico.
Importance of Plains
1. Plains provide good agricultural ground.
2. They facilitate mechanization in agriculture.
3. The facilitate the development of human. Settlements.
4. They provide Good grounds for the rearing of animals, e.g. the sudan savanna region of West Africa.
5. Some plains are important for their mineral deposites, e.g. petroleum in the coastal plains of Nigeria.
6. They promote the development of transport and communication routes.