- Exogenetic Forces: These are the external forces which act on the surface of the earth and bring physical stress and chemical actions on earth’s material and bring changes in the configuration of the earth’s surface. In other words exogenetic forces bring denudation on the surface of the earth and hence general lowering and levelling out of the surface.
- Denudation: It covers all the exogenic geomorphic processes under it. Weathering, mass movement, erosion, transportation, all comes under single term denudation. Denudation of a material is carried out in four phases:
- Weathering
- Transportation
- Erosion
- Deposition
- Source of Energy behind exogenetic processes are:
- Energy of the Sun
- Gradients created by tectonic factors
- Energy of the Sun: It should be noted that Sun’s energy are absorbed by the atmosphere. And hence all atmospheric process is induced by the Sun’s energy. These atmospheric processes are the main reason behind denudation. Hence we can say that Sun is the sole driving force behind all the exogenetic processes.
- Reasons of denudation: Basic reason behind denudation is the development of stress in the materials of earth. This stress are developed by two broad factor:
- Gravitational
- Atmospheric
- Gravitational Factor: Gravitational force which acts on a material of the earth surface is produced by the gradients created by tectonic factors. Gravitation produces pulling forces which in turn produces stress in the earth’s material. This stress developed in the material of the earth induces denudation among them.
- Atmospheric Factor: Temperature and precipitation are the two important elements of the atmospheric factors which directly and indirectly creates molecular stress among material of the earth surface.
- There is a variation in the intensity of climatic factors in different regions, due to different local factors such as:
- Altitudinal differences
- Aspect variation
- Varying amount of insolation received by a region
- Variation in wind velocity and direction
- Amount and kind of precipitation
- Relation between precipitation and evaporation
- Daily range of temperature
- Freezing and thawing frequency
- Depth of frost precipitation
- Variation in the intensity of action of exogenic geomorphic processes has been observed under same climatic condition on different earth’s material. This variation is due to the variation in the type and structure of rocks.
- Weathering: It is defined as the mechanical disintegration and chemical decomposition of material of the earth into products which are more stable in the conditions of that particular environment. Weathering is the initial step for many other aspects of hydrosphere, lithosphere and biosphere which can be explained below.
- Weathering provides sediments for erosion and deposition.
- Weathering contributes to the formation of soil by providing mineral particles like sand, silt and clay.
- Elements and compounds extracted from the rocks and minerals during weathering processes are the major source of nutrients for plants.
- Weathering releases ion salts from rocks and minerals which reaches to the ocean basin through leaching and runoff transport.
- Types of Weathering:-
- Physical or mechanical weathering.
- Chemical weathering
- Biological weathering
- Physical or Mechanical weathering: it is the weathering processes through mechanical method which depends on some applied force such as:
- Gravitational forces generated by overburden pressure, load and shearing stress.
- Expansion forces produced by temperature changes, crystal growth or animal activity.
- Water pressure exerted by water during wetting and removal of pressure during drying.
- Chemical Weathering: It is the weathering of rocks through chemical process like solution, carbonation, hydration, oxidation and reduction. Through this processes rocks get decompose, dissolve or reduce into a fine clastic state. Agents of chemical reaction are:
- Water
- Oxygen
- Carbon Dioxide
- Heat etc.
- Biological weathering: Weathering of materials on the surface of the earth due to growth or movement of organism.
- Burrowing and wedging by organisms like earthworm, termites, rats etc
- Ploughing and cultivating soil by humans.
- Growth of vegetation on earth’s material.
- Decaying plants and animals enhances chemical reaction as they produce carbonic, humic and other acids.
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