Geomorphic agents and processes PDF

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Geomorphic agents and processes...

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Geomorphic agents and processes The geomorphic agents are those which are responsible for creating certain reliefs. These agents may be water, wind, waves, glaciers etc. And the geomorphic processes are those which shape the earth by creating certain landforms with the help of these agents.

Endogenic Forces   

Endogenic forces are those internal forces which derive their strength from the earth’s interior and play a crucial role in shaping the earth crust. Examples – mountain building forces, continent building forces, earthquakes, volcanism etc. The endogenic forces are mainly land building forces.

The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth. Diastrophism- All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They include: (i) orogenic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust (ii) epeirogenic processes involving uplift or warping of large parts of the earth’s crust (iii) earthquakes involving local relatively minor movements (iv) plate tectonics involving horizontal movements of crustal plates Orogeny is a mountain building process whereas epeirogeny is continental building process. All these processes cause pressure, volume and temperature (PVT) changes which in turn induce metamorphism of rocks. Volcanism- Volcanism includes the movement of molten rock (magma) onto or toward the earth’s surface and also formation of many intrusive and extrusive volcanic forms. Earthquake -(also known as a quake, tremor or temblor) is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves.

Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. Exogenic Forces Exogenic forces are those forces which derive their strength from the earth’s exterior or are originated within the earth’s atmosphere. Examples of forces – the wind, waves, water etc. Examples of exogenic processes – weathering, mass movement, erosion, deposition. Exogenic forces are mainly land wearing forces.

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Exogenic forces can take the form of weathering, erosion, and deposition. Weathering is the breaking of rocks on the earth’s surface by different agents like rivers, wind, sea waves and glaciers. Erosion is the carrying of broken rocks from one place to another by natural agents like wind, water, and glaciers. The actions of exogenic forces result in wearing down ( degradation) of relief/elevations and filling up (aggradation) of basins/ depressions, on the earth’s surface. The phenomenon of wearing down of relief variations of the surface of the earth through erosion is known as gradation. 

WEATHERING-Weathering is the breakdown of rocks at the Earth's surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. There are three types of weathering, physical, chemical and biological. Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water. There are two main types of physical weathering: Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.Exfoliation occurs as cracks develop parallel to the land surface a consequence of the reduction in pressure during uplift and erosion

Chemical weathering is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic. There are different types of chemical weathering, the most important are:

Solution - removal of rock in solution by acidic rainwater. In particular, limestone is weathered by rainwater containing dissolved CO2, (this process is sometimes called carbonation).

Hydrolysis - the breakdown of rock by acidic water to produce clay and soluble salts.

Oxidation - the breakdown of rock by oxygen and water, often giving iron-rich rocks a rustycoloured weathered surface.

Biological Weathering-Living organisms contribute to the weathering process in many ways: Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart. Many animals, such as these Piddock shells, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock.

1. Erosion-erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location[1] (not to be confused with weathering which involves no movement). (i) Corrosion - It involves the dissolution of the soluble material through the process of disintegration and decomposition of carbonate rocks. The dissolution of soluble materials and minerals from the rocks takes place through the process of solution. It further depends on the nature of rock, solubility of solids, contact type of solvents and solids and ratio between volume of solvents and solids. (ii) Abrasion - It involves the removal of the loosened materials of the rocks by different erosional processes in differentiate manner. The degree of abrasion depends upon various factors like the nature of erosional tools, nature of erosional processes, nature if geomaterials, force of erosional processes and many more. (iii) Hydraulic action - It involves the breakdown of rocks, due to the exertion of the pressure by currents of water and waves of sea. This action is the mechanical loosening and removal of material of rocks by water alone. The chemical erosion, abrasion and hydraulic action are so much related to each other that each of these actions cannot successfully operate without the other. (iv) Attrition - It involves the wear and tear of the erosional tools. The cubbles, pebbles and bolders while moving downwards with water, gets collide against each other and are fragmented into smaller pieces. They are so much broken down to pieces that they get transformed into fine particles of sands and gets transported down in suspension. (v) Deflation - It involves the removing, lifting and blowing away loose and dry particles of land and dust by winds. The long and continuous deflation removes most of the loose materials and and large depression know as blow out are formed.

2. Transportational work : (i) The processes like floatation, suspension, solution, saltation and traction accomplishes certain transportational work. (ii) Running water transports the sediments through traction, suspension and solution.

(iii) The process of saltation involves the transportation of load with currents of water, where the load moves downwards through the valley floor. It works in an extremely slow manner. (iv) Traction involves the downstream movement of the loose materials of the valley floor. The load are usually gravel, pebbles, cobles and bolders. (v) The soluble materials get dissolved in water and become invisible and are transported downstream through the method of solution. (vi) The materials get dissolved in a suspended form through groundwater. (vi) The transportational work of sea wave differs from the other agents of transportation. The materials get transported from coast towards the sea and again from the sea towards the coast. (vii) The materials involved in the transportational work of sea waves ate sand, silt, gravels, pebbles, cobles and bolders. 3. Deposition (i) The deposition of the sediments by the streams depends upon a number of factors like decrease in channel gradient, decrease in stream velocity, decrease in volume and discharge of water, obstruction in channel flow, increase in sediment load, and spreading of river water over large areas. (ii) Depositional work by the streams, is carried with an decrease in the velocity of stream, which reduces the transporting capacity of the streams and as a result it leaves additional sediments to settle down. Sedimentation takes place in the flood plains, river beds and river mouths. (iii) Depositional work by groundwater, takes place when water becomes obstructed or over saturated. The groundwater receives more solutes, due to the continuation of the chemical erosion of carbonate rocks. As the movement of the groundwater is slow, it cannot carry enough sediments. As a result sedimentation and chemical erosion takes place together. Large size sediments gets easily settle down, while the fine sediments are kept in the suspended form. (iv) Depositional work by sea waves, is the most variable and temporary in character because, the currents bring the sediments seawards and deposit them at lower segments of wave cut platforms. These sediments are again brought back to the coast. When an equilibrium level is achieved between the incoming supply of sediments and removal of sediments, a profile of equilibrium is achieved. (v) Depositional work by wind, is very significant because, features like sand dune and loess are formed. The sediments get deposited due to the decrease in the wind speed and obstruction caused by forest, swamps, lakes, rivers, walls and many more. Sands get deposited on both windward and leeward side of these obstructions. The accumulated sands on other side of the obstruction are called sand shadows, while the accumulated sands between the obstructions are called sand drifts. (vi) The depositional work by glaciers, which carry the rock debris are called glacial drifts which contains till, ice contact stratified drift, outwash and many more. They are divided into englacial debris, that exist on the surface of the glacier ; superglacial debris, that exist on the surface of the glacier ; subglacial debris, that exist on the base of the glacier....