Different Landforms on the earth crust are caused by both endogenetic forces and exogenectic forces
The forces, which the affect crust of the earth, are divided into two broad categories on the basis of their sources of origin, they are Endogenetic Forces and Exogenetic Forces. The Endogenetic Forces (Diastroph forces, volcanic eruption, Earthquak etc.) give rise to several vertical irregularities, which leads to the formation of numerous varieties of relief features on the earth surface (e.g. Plateau, mountain, plain, lakes, faults, folds etc).
Compressional Forces and Tensional Forces. Due to compressional forces, the rock strata gets folded. For example Folded Mountain Himalaya
Faults : Cracks, Fractures and Faulting are included in it. Faults are formed due to the combined effect of both the compressional and tensional forces.
Rift valley are actually formed due to displacement of crustal parts and subsidence of middle portion between two normal faults. The Dead Sea of Jordan is located in a Rift valley.
When the middle portion remains at place and the two side blocks move downwards, the Block Mountains are formed. Satpura mountains in India, Black Forest and Vosages in Germany.
The main function of the exogenetic forces on the surface of the earth is denudation which includes, the processes of weathering and erosion.
Weathering: The process of disintegration and decomposition of rocks, due to physical, chemical or biological factors, at their own place is known as weathering. Based on the causes, the process of weathering is classified into three types:
A. Physical or Mechanical Weathering
- Due to insolation (Temperature)
- Due to Frost action
- Due to Friction
- Due to Pressure
B. Chemical Weathering
- By oxidation
- By Carbonation
- By Hydration
C. Biological Weathering
- By Plants
- By Animals
- Due to Human Activities
Erosion: Large scale transportation of the weathered materials is termed as erosion
Running Water (River)
The area drained by a river and its tributaries known as River Basin Catchment Area. Differ landforms by a river are:
- V-shaped Valley : During its youthful stage the river down-cuts (vertical erosion or valley deepening) its valley. This results into formation of V-shaped valley, which is very deep and narrow and both of its sides meet together at the valley floor. In India, indus gorge, Shipkila gorge and Dihang gorge are highly famous. Though lateral erosion is observed in the valley, down-cutting of the river is most dominant, making lateral erosion negligent. It is divided into two types on the basis of its size and shape - Gorge and Canyon. Generally Gorge is very deep and narrow valley Sometimes it is formed as a result of fast withdrawal of waterfalls. Canyon is the extended form of Gorge. Its side-walls a comparatively more vertical. The best example of Canyon in the world is the Grand Canyon on the Colorado river of USA.
- Waterfalls and Rapids: Water falls are caused because of sudden descents or abrupt breaks in the longitudinal course of the river, A waterfall may be defined as a vertical drop water of enormous volume from a great height in the long profiles of the rivers. Niagra fall North America and Victoria fall on the Zambezi river of Africa are leading examples of waterfall. The Jog or Gersoppa falls on the Sharavati river in the state of Karnataka (India) falls from a height of 260 m. Dhuandhar fall on the Narmada river and Hundru fall (97 m) on the Subarnrekha riverare well known for their scenic beauty. Rapids are of lesser height with respect to waterfalls.
- Alluvial cones: When rivers leave the mountains and enter the plains, their channel gradient drops substantially, resulting into drop in the load carrying capacity of the river. Consequently, load consisting of finer to coarser and big-sized materials coming from the upstream is deposited at the point of break in slope of foothill zone and thus alluvial cones are formed. When several alluvial fans get combined, it forms Bhabhar region.
- Alluvial Fans: When river descends from the hills, it spreads the load in a vast area. This results into the formation of fan-shaped plains, called alluvial fans.
- Meanders: While flowing through the plains, the river stream flow take several turns and makes meanders. River meandering refers to the bends of longitudinal courses of the rivers and are 'S' shaped.
- Oxbow Lake: When the river straightens after abandoning its meandering path, then the abandoned part forms the oxbow lake.
- Levees : The narrow belt of ridges of low height built by the deposition of sediments by the spill water of the stream on its either banks is called natural Levee or embankments. These are formed due to the deposition of the load carried by the river as it moves ahead.
- Delta: The depositional feature of almost
triangular shape at the mouth of a river
debouching either in a lake or a sea, is
called delta. These are formed when the
river flow.-through low lying plains and
consequently its load carrying capacity reduces due to decrease in its speed. It resembles the shape of the Greek-alphabet Delta.
There are various kinds of Deltas such as :
- Arcuate type : Delta of Nile River, Ganga- Brahmaputra Delta
- Bird-foot type : Mississippi - Missouri Delu
- Estuarine type : Narmada river Delta and Tap: river Delta in India.
- Cuspate type : Ebbro delta in Spain
Seawater carves different landforms with the help of sea-waves, currents, tidal waves or tsunamis
- Coastal Cliffs: Steep rocky coast rising almost vertically above seawater, is called cliff.
- Coastal Caves: The coastal landform formed due to heavy sea-wave erosion on the coastal rocks having fissure, fracture and weak rocks.
- Stacks: The natural arcs formed due to the coalescence of two caves are not permanent landforms. After collapsing the natural arc, the left portion projecting well above the sea-level is called stack.
- Beach: Temporary or short-lived deposits of marine sediments, consisting of sands, shingles etc, on the .seashore are called beaches. Beaches are deposited by breaker waves between high and low tide waters. These are formed when sea is calm and winds are of low velocity.
- Lagoons are formed when the coves or bays are almost completely enclosed by bars. Chilka Lake and Pulicat Lake on the east coast and Vembanad Lake on the west coast of India are lagoon lakes.
Glaciers : The moving ice mass down slope under the impact of gravity is called glacier. Snow line is generally defined as a zone between permanent and seasonal snow.
They formed on high mountains are long and narrow because they are formed in an abandoned river valley. These are known is 72 km long, is the largest of all the Indian glaciers. Different landforms carved out by glaciers are:
- U-shaped Valley : U-shaped valleys are formed due to vertical erosion by the glaciers in the already existing river valley.
- Hanging Valley : The valleys of tributary structure with steep walls, is formed, it is called cirque.
- Horns : The pyramidal or triangular-faceted peak, formed due to recession and intersection of three or more cirques, is called horn. The Matterhorn Peak of Switzerland is very famous.
The wind is the most active agent of gradation in the arid and semi-arid regions where rainfall is very scanty and the ground surface is covered with loose particle of soil in the absence of both moisture and vegetation cover.
Mushroom-Rock : The rocks having broad upper part and narrow base resembling an umbrella or mushroom are called mushroom rocks. These are the result of abrasional work of wind in which the base of the rock is abraded rigorously.
Sand Dunes: The heaps or mounds of sand deposited by wind, are called sand dunes. Sand dunes keep their position changing the direction of wind. Sand dunes of crescentic shape having two horns are called Barchans. Loess: Loess plain are the extensive plains formed by the deposition of very thin soild particles brought by the wind in the outskirt of the desert region. Loess turns into very fertile soil when it gets water.
Playa: The temporary lakes created by the ephemeral streams in the bolsons, i.e. basins enclosed by hills in desert regions are called playas.