Landforms of the Earth
A landform in the earth sciences and geology sub – fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography. Landform elements also include seascape and oceanic waterbody interface features such as bays, peninsulas, seas and so forth, including sub – aqueous terrain features such as mid – ocean ridges, volcanoes, and the great ocean basins.
Major Landforms :
Mountains, plateaus and plains. Mountains An uplifted portion of the earth’s surface is called a hill or a mountain. Mountains are classified into the following four types.
1. Fold Mountains :
These are formed by folding of crustal rocks by compressive forces under the influence of tectonic forces. The major mountains include the Alps of Europe, the Andes of South America, the Aravallis of India.
2. Block Mountains :
When great blocks of the earth’s crust are raised or lowered during the last stage of mountain building, block mountains are formed, e.g., Vosges in France, Black Forest mountains in Germany.
These are formed by the matter thrown out from the volcanoes, and are also known as mountain of accumulation, e.g., Mt. Mauna Loa in Hawaii, Mt. Popa in Myanmar.
4. Residual or Dissected Mountains :
They are known as relict mountains or mountains of circumdenudation. They owe their present form to erosion by different agencies, e.g. Nilgiris, Girnar and Rajmahal.
A plateau is an elevated area generally in contrast to the nearby area. It has a large area on its top and has an extensively even or undulating surface. Plateaus are of three types:
- Intermontane Plateaus :
- Piedmont Plateaus :
- Continental Plateaus :
The plateaus which are partly or fully enclosed by mountains are called intermontane plateaus. The highest and extensive plateaus of the world are Tibet, Bolivia and Mexico.
They are situated at the foot of a mountain and are bounded on the opposite side by plain or an ocean, e.g., Appalachian ( USA ), Patagonia ( Argentina ).
These plateaus rise abruptly from lowlands or sea and are the result of a continental uplift producing large tablelands like plateaus of Brazil, South Africa, Chhotanagpur, Shillong.
Plain is defined as a relatively flat and a low lying land surface with least difference between its highest and lowest points. On the basis of their mode of formation, plains are divided into three types :
1. Structural Plains :
These are formed by the raising of a part of the sea floor usually bordering a continent, that is, continental shelf, e.g., Great Plains of Russia and USA.
2. Erosional Plains :
When an elevated tract of land, for instance, a mountain hill is worn down by process of erosion, erosional plains are formed. These are found in river, ice or wind eroded regions, e.g., Northern Canada, Northern Europe, West Siberia.
3. Depositional Plains :
These plains are formed by filling – up of sediments into depressions along foothills, lakes. The deposition of sediments, brought down by large rivers, in the depression eroded areas form riverine or alluvial plains, e.g., Indo – Gangetic, Hwang – Ho, Po plains ( Italy ), Nile ( Egypt ).
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