Go through these RBSE Class 11 Geography Notes Chapter 9 Denudation contain important concepts so that students can score better marks in the exam.
Rajasthan Board RBSE Class 11 Geography Notes Chapter 9 Denudation
→ The nature of landforms keeps on changing. Endogenetic forces build uneven landforms on the earth’s crust, while exogenetic forces always remain active in levelling them.
→ The process by which the cover of rocks of the crust gets eroded and removed, is called Denudation.
→ Weathering, erosion and mass translocation are included in denudation.
- The breaking down of rocks by disintegration and decomposition at their own place by physical and chemical actions is called Weathering.
- Weathering is affected by the structure and organization of rock, slope of land, diversity in climate and vegetation.
Types of Weathering
- On the basis of the factors of disintegration and decomposition, weathering is classified into the following types: physical weathering, chemical weathering and biological weathering.
- Disintegration of rocks by insolation, frost, water and air pressure is called Physical Weathering.
- Change of rocks into new. compounds by the action of water and gases in a chemical process is called Chemical Weathering.
- Disintegration and decomposition occurring due to living-organisms found on the earth’s surface is called Biological Weathering.
- Physical weathering is classified in the form of Block Disintegration, Exfoliation, Frost Weathering and Pressure Release.
- Block Disintegration means disintegration of rocks into pieces, Exfoliation means breaking of rocks in form of shells, Frost Weathering means fragmentation by freezing and melting of snow, Pressure Release means cracks appearing in the rocks by upper pressure.
- Chemical weathering is classified in the form of Oxidation, Carbonation, Desilication, Hydration and Dissolution.
- Oxidation means oxygen changing into oxides, Carbonation means carbon-dioxide dissolving in water to give carbonic acid, Desilication means separation of silica from rocks, Hydration means absorption of water by rock minerals, Dissolution means dissolving of substances in water.
- Biological weathering is classified in the form of weathering by vegetation, weathering by animals and weathering by humans.
- Weathering by vegetation means breaking of rocks by trees, Weathering by animals means disintegration of rocks by animals, Weathering by humans means fragmentation due to various human activities.
- The word Erosion is made from the Latin word ‘Erodere’, the meaning of which is to rub or to nibble.
- Erosion is a dynamic process in which rocks keep on disintegrating by being rubbed, eroded, translocated or transported through glaciers, underground water, waves, air and rivers.
- The process of erosion takes place due to corrosion, attrition, hydraulic action, corrosion, deflation, cavitation and plucking.
- Eroded materials flow in three forms- dissolving, suspension and sliding.
- Deposition is the process of accumulation of the flowing debris, when the speed slows down or the slope becomes gentle after the erosion.
- Movement and transfer of rock debris in massive amount along the slope by gravitational force is called Mass Translocation.
- Creeping down from the slopes, the rock particles accumulate in the foothills. This accumulation or pile of rocks-flour is called Talus.
- A cone-shaped accumulation of loose rocks is called Talus Cone.
Differentiation of Mass Translocation
- Mass Translocation is classified in the form of gradual flow, rapid flow and extreme rapid flow.
- Earth Creep, Rock Creep, Talus Creep and Soil Creep are the forms of gradual flow.
- Earth flow, Mudflow and Sheet flow are the forms of rapid flow.
- Landslide, Rock Slide, Rock Fall, Landslip, Debris Fall and Slumping are the forms of extreme rapid flow.
Cycle of Erosion
- The concept of Cycle of Erosion was propounded by William Morris Davis in 1899.
- Landscape is regarded as the result of structure, process and stage by Davis.
- Period of stages is based upon the mobility of process and rock structure.
- Davis classified the cycle of erosion into the form of youth stage, mature stage and old stage.
- Davis called the flat plain part formed after the process of erosion as Pedeplain.
Penck’s Cycle of Erosion
- Walter Penck considered the cycle of erosion as the sum of the stages of development of landscapes, their uplift rate and inter-relations of their degradation.
- Penck classified the cycle of erosion into three time periods: Aufstegende, Gleighformige and Abstegende.
Denudation Notes Important Terms
→ Denudation: The physical process of stripping off the covering or removing the surface of rocks and land, in which weathering, erosion and mass translocation are included.
→ Endogenetic Force: Force originated from the internal part of earth due to which horizontal and vertical movements occur in the earth.
→ Exogenetic Force: Force originating or working on the surface of earth which is always active in levelling the earth’s surface.
→ Disintegration: The process of breaking down or splitting of rocks into the pieces by physical processes is called disintegration.
→ Decomposition: The process of decay of the rocks by dissolving as a result of corrosion of component minerals by chemical actions. In other words, decomposition is the process by which organic substances are broken into simpler matter.
→ Chemical Weathering: A process of weathering under which decomposition begins in the rocks due to chemical changes. By this, erosion of rocks takes place, which is called Chemical Weathering. Chemical weathering occurs mainly in the form of oxidation, carboniation and hydration.
→ Mechanical Weathering: The process of disintegration in the rocks due to physical factors like insolation, frost, air etc.
→ Humid tropics: The tropical regions where high temperature and high humidity are found in most duration of the year are called Humid tropics.
→ Insolation: Radiation energy received by the earth or other planets from the sun is called Insolation.
→ Frost: A deposit of small white ice crystals formed on the ground or other surfaces when the temperature falls below freezing point.
→ Block Disintegration: In hot, desert regions, cracks occur in the rocks due to daily extreme range of temperature. Over the passage of time, these rocks disintegrate into large pieces. This is called Block Disintegration.
→ Exfolation: The breaking of rocks in the form of shells when the upper layer of rocks remain heated and the inner layers cool down.
→ Frost Weathering: In extreme cold regions, the breaking down of rocks due to the freezing and melting of water in the cracks of rocks on regular basis is called Frost Weathering.
→ Pressure Release: When the removal of upper rocks reduces the pressure on lower rocks, then cracks start appearing in rocks. This process is called Pressure Release.
→ Oxidation: The process of combined effect of the mixture of water and oxygen on the minerals of rocks, by which oxides are formed in the minerals and the rocks start decomposing. This is called Oxidation.
→ Carbonation: The atmospheric carbon-dioxide gas (CO2) dissolves in water to form carbonic acid. On coming in contact with it, the lime rocks dissolve rapidly. This is called Carbonation.
→ Desilication: Process of separation of silica from rocks is called Desilication.
→ Igneous Rock: From the three large groups of rocks, the one which is formed when the hot and fluid magma cools down and solidifies, is called Igneous Rock.
→ Hydration: The process of denudation through which the decomposition of rocks takes place on their contact with water and they start breaking down. This process is called Hydration.
→ Dissolution: Rain water dissolves many types of acids and carbonic elements in the rock-materials and creates new chemical mixture. This reaction is called solution.
→ Biological/Organic Weathering: Biological weathering is the weakening and subsequent disintegration of rock by plants, animals and humans.
→ Corraosion: A type of erosive action in which pebbles, stones, boulders, rock particles, etc. along with any factor of erosion erode the land-surface by rubbing or scraping.
→ Attrition: The rock fragments or rock particles being carried by the air, water and glacier smash together and break into smaller particles. This process is called Attrition.
→ Hydraulic Action: The process of the erosion of rocks by the heavy pressure of river water or whirlpool is called Hydraulic Action.
→ Corrosion: The disintegration of rocks by chemical action is called Corrosion.
→ Deflation: The sand, dust or other unorganized rocks-flour being carried away by the winds from one place to another. This process is called Deflation.
→ Cavitation: Waves rising from whirlpool in river form many types of holes at the bottom of the river. This is called Cavitation.
→ Pot Hole: In the plains, a trough is formed at the bottom of the fast-flowing river, which originates as a result of the erosion by pebbles, stones and gravel carried by water-vortex. This is called pothole.
→ Plunge Pool: Deep trough built in a base rock by the erosion caused by pebbles and stones present in the water-vortex which fall down from a height with waterfalls.
→ Plucking: A major process of erosion by glacier through which erosion of the bottom of valley takes place is called Plucking.
→ Suspension: A natural process in which small pieces or particles of un-dissolved substances remain floating in a liquid or gas, but do not settle down due to being light. This process is called Suspension.
→ Deposition: The action of accumulating sediments or materials at a place carried from some other place by a natural process is called Deposition.
→ Sedimentary Rock: Layered rock formed by the deposition of sediments in lower parts of the earth’s surface by the processes of erosion.
→ Gravitational force: Gravitational force is a force that exists among all material objects in the universe. For any two objects or particles having non-zero mass, the force of gravity tends to attract them towards each other.
→ Talus: Creeping down from the slopes, the rock particles accumulate in the foothills. This accumulation or pile of rocks-flour is called Talus.
→ Talus Cone: A cone-shaped accumulation of loose rocks in the foothills, is called Talus Cone.
→ Earth Creep: The action of gradual creeping down of a large landmass from a mountain slope due to gravitational force is called Earth Creep.
→ Rock Creep: The action of gradual creeping down of rock fragments from the height along the slope due to gravitational force is called Rock Creep.
→ Soil Creep: The action of gradual creeping down of soil and rocks-flour from the height along the land-slope due to gravitational force is called Soil Creep.
→ Mudflow: Mudflow is the rapid flow of mud that mixed with sufficient quantity of rainwater or melting snow, so as to liquefy the entire mass and cause the flow.
→ Debris Fall: A type of landslide in which debris collectively falls downwards from the mountain slope or highland due to gravitational force is called Debris Fall.
→ Cycle of Erosion: A major principle of Geomorphology formulated by W.M. Davis.
→ Lateral Erosion: A concurrent process called lateral erosion refers to the widening of a stream channel or valley. When a stream is high above its base level, downcutting will take place faster than lateral erosion; but as the level of the stream approaches its base level, the rate of lateral erosion increases.
→ Pedeplain: Shape-less low flat plain formed in the last stage of aquatic erosion cycle in humid climatic region, on which ruins of hard rocks are found in the form of mounds.
→ Doab, Interfluve or Mesopotamia: The part located in the middle of two rivers interconnecting at a place is called Doab.
→ Aufstegende: According to Penck, the first stage of Erosion Cycle in which landforms develop rapidly.
→ Gleighformige: According to Penck, the mid stage of the development of landforms.
→ Abstegende: According to Penck, the last stage of the development of landforms.