Module 2: Exogenic Forces (PDF)

Module-2; Dynamic and Geomorphic Processes of the Earth 3. EXOGENIC FORCES AND THEIR RESULTANT LANDFORMS 3.1 EXOGENIC FORCES: DEFINITION AND TYPES: The forces which derive their energy from the earth’s exterior or originate within the earth’s atmosphere are called exo...

Module-2; Dynamic and Geomorphic Processes of the Earth 3. EXOGENIC FORCES AND THEIR RESULTANT LANDFORMS 3.1 EXOGENIC FORCES: DEFINITION AND TYPES: The forces which derive their energy from the earth’s exterior or originate within the earth’s atmosphere are called exogenic forces. Exogenic processes, including the action of water, ice and wind, predominantly involve denudation, that is, the removal of material, and thus generally lead to a reduction in elevation and relief. Types of Exogenic Processes: The gradational or plantation work of the earth’s surface irregularities is accomplished through (i) Degradation and (ii) Aggradation. Under the Degradation the upstanding landmass is lowered down by weathering, mass movement and erosional activities. This mechanism of plantation is termed as level down. In parallel to this, Aggradation is the deposition of the weathered and eroded material and this mechanism of plantation is called level up. 3.2 MECHANISM OF EXOGENIC PROCESSES: As there are different physio-climatic regions owing to variations in thermal gradients created by latitudinal, seasonal, and land- use spread on the surface of the earth, the exogenic geomorphic processes vary from region to region. 3.3 WEATHERING AND MASS WASTING: Weathering is the action of elements of weather and climate over earth materials to reduce them to fragmental state. It is an in- situ or on-site process, as very little or no motion of materials takes place in weathering. The process of weathering is conditioned by many complex geological, topographic, climatic, and vegetative factors. Climate played the most vital role. There are three major groups of weathering processes: Physical or mechanical weathering can be considered as the disintegration of rock masses into blocks, boulders, cobbles and pebbles, sands, and silts due to variation in temperature, frost action, wind action and unloading of superincumbent pressure. Chemical weathering is the disintegration and decomposition of rock masses due to chemical responses. Oxidation, solution, hydration, carbonation, chelation, and hydrolysis, etc. are the most recognized chemical reactions which affect the chemical composition of the rock masses. Apart from the mechanical and chemical reactions, biological agents also affect the rock’s structure which includes floral (physical and chemical both), faunal (burrowing animals, worms and other organisms), and anthropogenic (mining, blasting of hills for road and dam construction, quarrying for building and industrial material, deforestation, agriculture and many more). Mass Movements: Movement of fragmented material, debris or rock-waste material down the hill slope under the influence of gravity is called mass movement or mass wasting. 3.4 EROSION, TRANSPORTATION AND DEPOSITION: Exogenic processes are generally called erosional processes which perform three-phase work i.e. erosion, transportation and deposition. The erosional work by different processes is performed through the mechanism of: a. Corrasion or Abrasion involves the removal of loosened materials of the rocks by different erosional processes in different manner. Erosion tools refer to all those solid materials (boulders, cobbles, pebbles, sands etc.) with the help of which erosional agents attack and abrade the rocks. The degree of abrasion depends on a host of variables, e.g. nature of erosional agents such as rivers, groundwater, sea-waves, glacier, wind etc., nature of erosion tools, nature of geomaterials, force of erosional processes, gradient etc. b. The mechanism of corrosion involves dissolution of the soluble materials through the process of disintegration and decomposition of carbonate rocks, which is effectively corroded by running water, groundwater and sea waves. c. The mechanism of corrosion involves dissolution of the soluble materials through the process of disintegration and decomposition of carbonate rocks, which is effectively corroded by running water, groundwater and sea waves. d. The breakdown of rocks due to pressure exerted by water currents of the rivers and sea waves is termed as Hydraulic action. It is the mechanical loosening and removal of materials of rocks by water alone without the help of erosion tools. e. Deflation is the process of removing, lifting and blowing away dry and loose particles of sands and dust by winds.  The transportation and deposition of sediments vary depending on the agent involved, such as streams, sea waves, wind, or glaciers. Streams transport materials downstream, with soluble elements dissolving in water, while sea waves cause cyclic movement of sediments between the coast and sea. Wind transportation is multi-directional, carrying finer particles over long distances, while heavier particles move in stages. Glaciers transport debris along valleys or on the ice surface. Deposition occurs when the transporting agent loses energy. For example, in streams, deposition happens with reduced velocity, while wind deposits sediments when obstructed, forming features like sand dunes. Glaciers deposit unsorted materials known as tills or moraines. 3.5 RESULTANT MAJOR LANDFORMS: Endogenic and exogenic forces shape the Earth's surface, creating distinct landforms categorized into three broad orders. The first order includes large-scale features like continents and ocean basins, formed primarily by endogenic forces. The second order consists of structural landforms like mountains, plateaus, plains, and rift valleys, shaped by endogenic forces and refined by exogenic processes. Third-order, or micro-level landforms, result from erosional and depositional activities, such as valleys, cliffs, dunes, and deltas, often influenced by atmospheric processes. 3.6 MOUNTAINS: Mountains are the most awe-inspiring landform on the surface of the earth. A mountain is an elevated portion of the Earth’s crust, generally with steep sides that show significant exposed bedrock, which covers around 27% of the total earth’s surface. According to the Oxford English Dictionary, a mountain is defined as “a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relative to the adjacent elevation, is impressive or notable.” On the basis of their mode of origin, the mountains have been classified as: a. Folded Mountains: Folded mountains are formed due to folding of crustal rocks by compressive forces generated by endogenetic forces coming from within the earth. Rockies, Andes, Alps, Himalayas, Atlas etc. are the examples of folded mountains. b. Block Mountains: Block mountains are the result of faulting caused by tensile and compressive forces motored by endogenetic forces coming from within the earth. The Vosges in France, Black Forest Mountains in Germany are the typical examples of block mountains. c. Dome Mountains: These mountains are originated by magmatic intrusions and upwarping of the crustal surface. Examples: normal domes, lava domes, batholithic domes, laccolithic domes, salt domes etc. Typical example of domed mountain is Weald in southeast England.  Mountains of Accumulations: These mountains are formed due to accumulation of volcanic materials. Thus, these are also called volcanicc mountains. Mount Mauna Loa in Hawaii Islands, Mount Popa in Myanmar, Vesuvius in Italy, Cotopaxi in Ecuador and Fuji Yama in Japan are examples of volcanic mountains.  Circum-erosional or Relict or Residual Mountains: Soft rocks are worn down into sand and the hard rocks are left standing up in the area that has been reduced in height. These are called relict or residual mountains. Hills like the Nilgiris, the Parasnath, the Rajmahals and the Aravallis in India are examples of residual mountains. The Significance of Mountains: 1. Storehouse of Resources 2. Abundant Sources of Water 3. Generation of Hydro-electricity 4. Formation of Fertile Plains Downstream 5. Hotspots for Biodiversity 6. Home of numerous Indigenous people 7. Natural Political Frontiers 8. Influence the Climate 9. Major Tourist Attractions 10. Sacred landforms on the Earth 3.6 PLATEAUS: Plateau or Plateaus is an extensive area of flat upland usually bounded by steep slopes on all sides but sometimes enclosed by mountains. The essential criteria for plateaus are low relative relief and some altitude. It covers about 18% of the earth’s surface. The vertical expansion is normally 600 metres above sea level, but there are also plateaus of Tibet and Bolivia, more than 3600 metres above sea level. On the basis of their geographical location and structure of rocks: a. Intermontane Plateau: The plateau which are bordering the fold mountain range or are partly or fully enclosed within them are the intermontane plateaus. Notable examples include the Tibetan Plateau, which rises over 4,500 meters and is surrounded by folded mountains like the Himalayas and Karakoram. The Colorado Plateau, over one kilometer high, features the Grand Canyon and gorges carved by rivers. Other examples include the plateaus of Mexico, Bolivia, and Iran. b. Piedmont Plateau: The plateaus that are situated at the foot of the mountains and are bounded on other sides by a plain or an ocean are called piedmont plateau, The plateau of Malwa in India, Patagonia facing the Atlantic Ocean and the Appalachians situated between the Appalachian Mountain and the Atlantic Coastal Plain in U.S.A are their examples.( also called the plateaus of denudation) The Significance of Plateaus: 1) Storehouse of Minerals(gold from the Plateau of Western Australia; copper, diamonds and gold from the Plateaus of Africa and coal, iron, manganese and mica from the Chota Nagpur Plateau in India.) 2) Birthplace of various waterfalls(In India, two important waterfalls in the plateau regions are Hundru falls in the Chota Nagpur plateau on the river Subarnarekha and the Jog falls in Karnataka on the river sharavati.) 3) Cool Climate(South and East Africa) 4) Useful for Agriculture and Animal-rearing 5) Tourist attraction 3.7 PLAINS: A low-lying relatively flat or slightly rolling land surface with very gentle slope and minimum local relief is called a plain, average height of less than 200 metres. On the basis of their mode of formation, A. Structural Plains: These plains are mainly formed by the uplift of a part of the sea-floor or continental shelf. These are located on the borders of almost all the major continents. The south eastern plain of the United States formed by the uplift of a part of the Gulf of Mexico is an example of this type of plain. B. Erosional Plains: These plains are formed by the continuous and a long-time erosion of all sorts of upland. The surface of such plains is hardly smooth. These are therefore also called peneplains which means almost a plain. The Canadian shield and the West Siberian plain are examples of erosional plains. C. Depositional Plain: Plains are formed by various deposition processes and are classified accordingly. Riverine or alluvial plains, like the Indo-Gangetic Plain and the Hwang-Ho Plain, form from river deposits. Lacustrine plains, such as the Kashmir and Manipur Valleys, arise from lake sediments. Glacial plains, like those in Canada and Northwestern Europe, are formed by glacial deposits, while loess plains, found in North-Western China, result from wind-deposited fine dust in arid regions. The Significance of Plains: 1) Most Fertile Soil 2) Improved transport and communication system 3) Favourable climate 4) Development of industries 5) Centres of Civilizations (civilizations of the Indus and the Nile Valley.)