Types of plains

What is a plain?

A Plain is an area of lowland, either level or undulating. It seldom rises more than a few hundred feet above the sea level. Plains usually are best forms of land and are often intensively cultivated. Population and settlements are normally concentrated on plains and when they are traversed by rivers, as most of them are, their economic significance is even greater.

Examples: The Gangetic Plain, The Mississippi Plain and The Yang-tze Plain. Some of the most extensive temperate plains are grasslands like Russia Steppes, The North American prairies and Argentina’s Pampa. Plains are majorly grouped into three categories based on their modes of formation:

Structural plains:

These are structurally depressed areas, which make up some of the most extensive natural lowlands on the earth’s surface. They are formed from horizontally bedded rocks relatively undisturbed by the crust movements of the earth. These include The Great Plains of the Russian Platform, The Great Plains of USA and The Central Lowlands of Australia.

Depositional plains:

These are formed by the deposition of materials brought by various agents of transportation such as rivers, winds, waves and glaciers. Their fertility and economic relevance depend greatly upon the types of sediments laid down.

Depositional Plains are grouped into the following:

Alluvial plains, formed by rivers:

• Alluvial plain, formed over a long period of time by a river depositing sediment on its flood plain or bed which becomes the alluvial soil. The difference between a flood plain and an alluvial plain is that the flood plain represents the area experiencing flooding fairly regularly at present or recently, whereas an alluvial plain includes areas where the flood plain is now and used to be, or areas which only experience flooding a few times a century.
• Flood plain, adjacent to a stream, river, lake or wetland that experiences occasional or periodic flooding.
• Scroll plain is a plain through which a river meanders with a very low gradient.
• Lacustrine plain is a plain that originally formed in a lacustrine environment, that is, as the bed of a lake.
• Lava plain is formed by sheets of flowing lava.

Glacial plains, formed by the movement of glaciers under the force of gravity:

• Sandur (plural sandar) is a glacial out-wash plain formed of sediments deposited by melt-water at the terminus of a glacier. Sandar consist mainly of stratified (layered and sorted) gravel and sandTill plain, a plain of glacial till that forms when a sheet of ice becomes detached from the main body of a glacier and melts in place depositing the sediments it carries. Till plains are composed of unsorted material (till) of all sizes.
• Abyssal plain is a flat or very gently sloping area of the deep ocean basin
• Planitia, the Latin word for plain, is used in the naming of plains on extraterrestrial objects (planets and moons), such as Hellas Planitia on Mars or SednaPlanitia on Venus.

Erosional Plains:

These plains are carved by the agents of erosion. Rain, rivers, ice and wind help smoothen out the irregularities of the earth’s surface, and in terms of millions of years, even high mountains can be reduced to low undulating plains. Such plains of denudation are described as pen plains, a word meaning almost-plains.

Rivers, in their course from source to sea, deepen their valleys and widen their banks. The projecting spurs are cut back so that the level ground bordering the level bordering the river is constantly widened. At the same time, the higher land between the rivers is gradually lowered.

In glaciated regions, glaciers an ice sheets sourced and levelled the land forming ice sourced plains. Hollow scooped out by the ice are now filled by lakes. These are extensive ice-sourced plains in northern Europe and northern Canada. Finland is estimated to have 35,000 lakes, occupying 10 per cent of the total land surface of the country.

Indo-Gangetic Plain:

The Indo-Ganga plains, also known as the "Great Plains," are large floodplains of the Indus and the Ganga–Brahmaputra river systems. They run parallel to the Himalaya Mountains, from Jammu and Kashmir in the west to Assam in the east and draining most of northern and eastern India. The plains encompass an area of 700,000 km and vary in width through their length by several hundred kilometres. The major rivers of this system are the Ganga and the Indus along with their tributaries; Beas, Yamuna, Gomti, Ravi, Chambal, Sutlej and Chenab.

Extent of the Indo-Gangetic plain across South Asia.The great plains are sometimes classified into four divisions:

• The Bhabhar belt — is adjacent to the foothills of the Himalayas and consists of boulders and pebbles which have been carried down by the river streams. As the porosity of this belt is very high, the streams flow underground. The bhabar is generally narrow about 7–15 km wide.
• The Terai belt — lies next to the Bhabar region and is composed of newer alluvium. The underground streams reappear in this region. The region is excessively moist and thickly forested. It also receives heavy rainfall throughout the year and is populated with a variety of wildlife.
• The Bangar belt — consists of older alluvium and forms the alluvial terrace of the flood plains. In the Gangetic plains, it has a low upland covered by laterite deposits.
• The Khadir belt — lies in lowland areas after the Bangar belt. It is made up of fresh newer alluvium which is deposited by the rivers flowing down the plain.

The Indus-Ganga belt is the world's most extensive expanse of uninterrupted alluvium formed by the deposition of silt by the numerous rivers. The plains are flat and mostly treeless, making it conducive for irrigation through canals. The area is also rich in ground water sources.

The plains are the world's most intensely farmed areas. The main crops are rice and wheat, which are grown in rotation. Others include maize, sugarcane and cotton. The Indo-Gangetic plains rank among the world's most densely populated areas.

Fauna

Until recent history, the open grasslands of the Indus-Ganga Plain were inhabited by several large species of animals. The open plains were home to large numbers of herbivores which included all three of the Asian rhinoceros (Indian rhinoceros, Javanrhinoceros,Sumatran rhinoceros). The open grasslands were in many ways similar to the landscape of modern Africa.

Gazelle, buffalo, rhinos, elephants, lions, and hippo roamed the grasslands, the same way as they do in Africa today. Large herds of elephants, gazelles, antelopes and horses lived alongside several species of wild cattle including the now-extinct Aurochs. In the forested areas, there were several species of wild pig, deer and muntjac. In the wetter regions close to the Ganga there would have been large herds ofWater Buffalo grazing on the riverbanks along with extinct species of hippopotamus.

So many large animals would have supported a large population of predators as well. Wolf, Dhole, Striped Hyena, Indian cheetah and Asiatic Lion would have hunted large game on the open plains, while tigers and leopards would stalk prey in the surrounding woods and sloth bears hunt for termites in both of these areas. In the Ganges there were large concentrations of gharial, mugger crocodile and river dolphin controlling fish stocks and the occasional migrating herd crossing the river.

Agriculture

Farming on the Indus-Ganga Plain primarily consists of rice and wheat grown in rotation. Other crops include maize, sugarcane, and cotton. The main source of rainfall is the southwest monsoon which is normally sufficient for general agriculture. The many rivers flowing out of the Himalayas provide water for major irrigation works. Due to a rapidly growing population (as well as other factors), this area is considered at high risk for water shortages in the future. The area constitutes the land between the river Brahmaputra and Aravli mountain ranges. The famous river Ganga and others such as Yamuna, Ghaghara and Chambal flow through the area.