Geomorphic Processes Class 11 Notes Geography Chapter 5 - CBSE

Chapter : 5

What Are Geomorphic Processes ?

  • The earth's crust is dynamic. It has moved and still moves vertically and horizontally. There are some powers that changes the earth. These are internal and external.
  • The earth's surface is being continuously subjected to by the external forces originating within the earth's atmosphere and by the internal forces from within the earth and it is ever-changing.

Geomorphic Processes

These refer to the chemical and physical interactions between the earth’s surface and the natural forces acting on it. It can be classified into:

Endogenic forces

  • These are generated in the interior of the earth, which are further classified into diastrophic and sudden movements. Diastrophic forces can be classified into
    epeirogenic and orogenic forces. Sudden forces comprise earthquake and volcanic eruptions.

Exogenic forces

  • These are generated outside the earth’s surface which are classified into weathering, mass movement, erosion, and deposition.

Weathering

It is the process of breaking down or the disintegration and decomposition of rocks. It is a static process. Weathering can further be
classified into chemical, physical, and biological weathering.

Mass Movement

It involves downhill movement of the weathered rock materials. The movement includes creeping, flowing, sliding, slumping, and falling. Mass movements can be slow or rapid.

Erosion

It is the displacement of weathered material through different agents of gradation.

Deposition

It is a geological process by which material is added to a landform or landmass.

Geomorphic Agents

They are the mediums through which the eroded materials are transported from the place of origin to the destination. These agents are Running water, Groundwater, Glaciers, Wind, Wave, and currents.

Endogenic Process

The energy genarated due to 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. This energy due to geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere. Due to variations in geothermal gradients and heat flow from within, crustal thickness and strength, the action of endogenic forces are not uniform and hence, the tectonically controlled original crustal surface is uneven.

Diastrophism

It refers to deformation of the Earth’s crust, and more especially to folding and faulting. Diastrophism can be considered part of geotectonics. It is also called tectonism. It is of two types: Orogeny and Epeirogeny. In the process of orogeny, the crust is severely deformed into folds. Due to epeirogeny, there may be simple deformation. Orogeny is a mountain-building process whereas epeirogeny is continental-building process.

Volcanism

It is the phenomenon of eruption of molten rock (magma). 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.

Exogenic Processes

These include geological phenomena and processes that originate externally to the Earth’s surface. They are genetically related to the atmosphere, hydrosphere, and biosphere and therefore to processes of weathering, erosion, transportation, deposition, denudation, etc. The exogenic processes derive their energy from atmosphere determined by the ultimate energy from the sun and also the gradients created by tectonic factors.

Weathering

It is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth’s atmosphere, waters, and biological organisms. It is the action of elements of weather on earth materials. Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements so weather and climate. In weathering no motion of materials takes place so it is in-situ or on site process. There are three types of weathering :

  • Chemical Weathering Processes is the weakening and subsequent disintegration of rock by chemical reactions. These reactions include oxidation, hydrolysis, and carbonation. These processes either form or destroy minerals, thus altering the nature of the rock’s mineral composition. A group of weathering processes viz, solution, carbonation, hydration, oxidation, and reduction on rocks to decompose, dissolve, or reduce them to a fine clastic state through chemical reactions by oxygen, surface/soil water, and other acids. Water and air along with heat must be present to speed up all the chemical reactions.
  • Physical Weathering Processes: Factors influencing the physical weathering are: (i) Gravitational Force
    Overburden Pressure, Load, and Shearing Stress; (ii) Expansion Forces Due To Temperature Changes, Crystal
    Growth, or Animal Activity; (iii) Water Pressures Controlled By Wetting And Drying cycles. They are mostly
    due to thermal expansion and pressure release. The repeated action of these processes cause damage to the
    rocks.
  • Biological Weathering is contribution to or removal of minerals and ions from the weathering environment and physical changes due to growth or movement of organisms. Burrowing and wedging by organisms such as earthworms, termites, and rodents help in exposing the new surfaces to chemical attack and assists in the penetration of moisture and air. Human beings by disturbing vegetation, ploughing, and cultivating soils, also help in mixing and creating new contacts between air, water, and minerals in the earth materials.

Significance Of Weathering

Weathering is responsible for the formation of soils and erosion and deposition. Biodiversity basically depends on depth of weathering. Erosion may not be significant when there is no weathering. Weathering aids mass wasting, erosion, and reduction of relief and changes in landforms. Weathering of rocks and deposition helps in the enrichment and concentration of certain valuable ores of iron, manganese, aluminium, and copper. It is an important process of soil formation.

Mass Movement

These movements transfer the mass of rock debris down the slopes under the direct influence of gravity. Air, water, and ice do not carry debris, but debris carry them. The movements of mass may range from slow to rapid.

Types of Mass Movements

Creep, flow, slide and fall; mass movements are active over weathered slopes than unweathered slopes. Mass movements are aided by gravity not any erosional agent. Mass movements do not come under erosion though there is shift of material.

Activating causes precede Mass Movements

(i) Removal of support from below to materials above through natural or artificial means; (ii) increase in gradient and height of slopes; (iii) overloading through addition of materials naturally or by artificial filling; (iv) overloading due to heavy rainfall saturation and lubrication of slope materials; (v) removal of material or load from over the original slope surfaces; (vi) occurrence of earthquakes, explosions, or machinery; (vii) excessive natural seepage; (viii) heavy drawdown of water from lakes, reservoirs, and rivers; (ix) indiscriminate removal of natural vegetation

Heave, flow and slide

These are the three forms of movements. The mass movements can be grouped into three types:

Slow movements, Rapid movements, and Land slide.

Erosion

Erosion involves acquisition and  transportation of rock debris. When massive rocks break into smaller fragments through weathering and any other process, erosional geomorphic agents like running water, groundwater, glaciers, wind, and waves remove and transport it to other places depending upon the dynamics of each of these agents.

Deposition

The process of laying down of sediment carried by wind, flowing water, sea, or ice.

Soil Formation

Soil is the collection of natural bodies on the earth’s surface containing living matter and supporting or capable or supporting plants. It is a dynamic material in which many chemical, biological, and physical activities take place constantly. It is the result of decay and is also a medium of growth. It is a changing and developing body. Soil's characteristics change from season to season. Too cold, hot, and dry conditions cause biological activity to slow down or stop. Organic matter increases when leaves fall and decompose.

Process Of Soil Formation

Weathering is the basic process for soil formation. The weathered material is transported and decomposed due to bacteria, lichens, and moss. The dead remains of plants and other organisms build up and increase the humus of the soil. Plants such as minor grasses, ferns, bushes, and trees thrive. The deep roots of plants and burrowing animals help a lot in soil formation.