Landform: Types, Processes in Formation, Gradation of Landform

Landform

Study of landforms helps in understanding influence of landforms in human life. It’s study includes characteristics of various forms of land surface. Surface of landform is rarely uniform in height or appearance over large areas. Mountains, plateaus and plains are major landforms on the continents. Land forms develop due to sudden changes caused by earthquakes, volcanoes, floods etc. or due to gradual changes that are more widespread and take place continuously.

Processes in Landform Formation

Landforms are caused due to the action of two natural processes on the surface of land- external processes which take place in the atmosphere and hydrosphere and affect the land surface. These act slowly, wearing down the highland and depositing materials in lowlands & internal processes that take place in the interior of the earth and cause changes on the land surface. These processes cause movements of the earths’ crust leading to formation of mountains and plateau. The nature of landforms at any place is thus the result of interaction of these processes at a given period of time, In the external processes changes in weather conditions affect most the rock, exposed on the surface and break them up into smaller particles. This process of breaking up of rocks by changes in weather phenomena such as temperature, moisture and precipitation is called weathering. Weathering takes place in situ.

Weathered particles are then transported by some moving agents and get deposited in the lowlands or on sea floor. Rivers, glaciers, winds and waves are the main agents of gradation (transportation)

The type of rocks has a great influence on the landforms developed in an area. Relatively stronger rocks like granite, quartzite and limestone with much hardness are not easily worn down. They give rise to upstanding mountains and hills. The soft rocks like shale, clay or loose sand forms bluff or knolls but turn into plains and valleys upon their weathering. Sedimentary rocks form plains or lands with gentler slope unlike the crystalline rocks. However, in wet and warm climate even hard limestone gets rapidly weathered. Thus climate of the area and the time taken in wearing down of rock also influence land forms.

Types of Landforms

Landforms are classified on the basis of the way they have been shaped and the main features by which they are recognised. There are following three major landforms-mountains, plateaus and plains.

1. Mountains

   An uplifted portion of the earth’s surface is called a hill or a mountain. On the basis of their origin or mode of formation the mountains are classified as structural or tectonic, residual or dissected and volcanic. All great mountain systems of earth are structural mountains. Both the fold and block mountains belong to this category. Himalayas of Asia are Fold Mountains. In our country, it is suggested that Narmada River flows through a subsided or faulted basin between Vindhyas and Satpuras which stand as Block Mountains to its north and south respectively. In Assam ranges also there have been much such faultings though there are no typical block mountains in the area. Residual mountains develop due to being worn down by agents of gradation (erosion). Hills like Nilgiris, Parasnath, Girnar and Rajmahal in our country are examples of this type. an

2. Plateau

   Plateau is elevated generally in contrast to the adjoining areas. It has a large area on its top unlike a mountain and has an extensively even or undulating surface. The great Deccan plateau with its slope towards east is a tilted plateau in our country. Very often, rivers and streams cut out deep valleys and canyons in a plateau region. On the basis of their situation there are three types of plateau-intermontane, continental and, piedmont plateaus. Continental plateaus rise abruptly from the lowlands or from the sea. Plateaus of Chota Nagpur and Shillong are of this type.

Peninsular India has a number of big and small plateaus. The great Deccan plateau consists of lava plateau of Maharashtra and the plateaus of Karnataka and Telangana. North-Eastern part of the old landmass of Peninsular India is occupied by a number of south Bihar plateaus collectively known as Chota Nagpur plateau. In the Himalayas, the highest plateau of a different type is in Ladakh.

3. Plain

   Plain is a relatively flat and a low-lying land surface with least difference between its highest and lowest points. These are usually lowlands. They are divided into structural, erosional and depositional plains. In India, Bhabar plain in U.P. along the Himalayas and extensive flood plains in Bihar are depositional plains. There are great Indian Delta plain of north India stretching in front of the Himalayas that include Ganga Delta on the east and Arid Plain of Rajasthan on the west. The delta of the combined Ganga-Brahmaputra rivers lies between their Hooghly-Bhagirathi and Padma-Meghna branches. The east coastal plains of India have smaller deltas of Mahanadi (Orissa), Godavari and Krishna (A.P.) and Kaveri river (Tamil Nadu).

Significance of Landforms

Each landform has its own significance to man. Mountains have protected mankind since long, also isolated man’s habitations and restricted his movements. Defeated man was given shelter by mountains. Passes in mountains allowed military invasions. They were the routes for explorers and settler. This allowed exchange of goods and ideas. Mountains provide natural frontiers between nations. Agriculture in mountains is only on limited scale. Most soil is washed out. Valleys between mountains are used for cultivation. There is developed transport system between plains and mountains now, and thus easy exchange of materials.

Forests are an important natural resource. They are not only places of tourists but also source of natural wealth to local people. Some plateaus are rich in minerals. The plains particularly in tropical and temperate region are very fertile for cultivation, easy means of communication and transport. These are areas of rich agriculture and industrial growth. These are the reasons why plains are teeming with people.

Gradation of Landforms

On the land surface, external as well as internal processes act in shaping the land surface to different landforms as well as in soil formation. External processes taking place in the hydrosphere and lithosphere affect weathering of rocks, erosion of land form surfaces and deposition of eroded soil to other places. The agents involved in these processes are water, wind, glaciers waves, etc. The internal forces originating in the interior of the earth change the surface of land to different landforms – mountains, plateaus, plains etc. These forces include movement of earth, earthquakes, volcanoes etc.

Thus, there are tectonic or earth-building forces that give rise to major landforms. There are erosive (that cause erosion) forces originating on the surface of the earth which destroy the elevations and also fill up the hollows of the earth’s surface. In other words, the tectonic or internal forces level up and the erosive or external forces level down the earth’s surface. As a result of the two opposite forces, the surface ultimately attains a common level or a grade. All the processes which tend to bring the surface of the lithosphere to such a common level are known as process of gradation. A surface thus reaches a grade (level) when there is neither erosion nor deposition any more.

Gradation is achieved by simultaneous process of degradation and aggradations

Degradation (or denudation) is the general wearing away of the land surface by external agencies. It includes the result of weathering, erosion and transportation. Process of weathering involves disintegration of parent rock at or near the earth’s surface. It begins as soon as the rock surface is exposed. Aggradation or deposition means the filling up of the depressions on the earth’s surface. The agents of aggradation are the same as those of erosion. In other words, each agent has its erosive as well as depositional role in changing the landscape slowly. Degradation or erosion is thus removal of land, whereas aggradation is the position of material in the lowlands leading to a gradual increase in level.

Normally, these two processes occur simultaneously in nature and are balanced. These together are referred to as gradation as this reduces the difference in height between highlands and lowlands.

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