GEOMORPHIC PROCESS

GEOMORPHIC PROCESS

The term geomorphic relates to the form of the landscape and other natural features of the earth’s surface. The forces causing physical and chemical changes on earth’s surface are known as geomorphic processes. All changes take place under the influence of certain forces working continuously within the earth as well as over the surface of the earth.

The exogenic and endogenic forces cause chemical actions and physical pressures on earth materials.

ENDOGENIC FORCES

• Internal force: 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.
• Source: This force energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.
• Effects: This energy due to geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere.
• Uneven actions: 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.
• Building force: The endogenic forces are mainly land building forces.
  • For Examples: mountain building forces, continent building forces, earthquakes, volcanism, etc.

Types of movement: The earth movements are mainly of two types: diastrophism and sudden movements.

1. Diastrophism: All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They include:
   • Orogenic processes: Involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust. They act tangentially to the earth’s surface, as in plate tectonics.
     • Tension produces fissures (force acting away from a point in two directions).
     • Compression produces folds (force acting towards a point).
   • Epeirogenic processes involve uplift or warping of large parts of the earth’s crust, thus it is a continental building process. They act along the earth’s radius and thus are also called radial movements.
     • When the direction of movement is towards, it is subsidence.
     • When it is away, it is uplift from the center. E.g.: Raised beaches, elevated wave-cut terraces, sea caves, etc.
2. Sudden movements: They cause considerable deformation over a short span of time, and may be of two types: earthquakes and volcanoes.

EXOGENIC FORCES

• External force: Exogenic forces are those forces which derive their strength from the earth’s exterior or origin within the earth’s atmosphere.

• Source: The exogenic processes derive their energy from the atmosphere determined by the ultimate energy from the sun and also the gradients created by tectonic factors.
• Wearing force: Exogenic forces are mainly land-wearing forces.
• Denudation: All the exogenic geomorphic processes are covered under denudation. E.g.: Weathering, mass wasting/movements, erosion, and transportation.
  • Weathering: Weathering is the breaking of rocks on the earth’s surface by different agents like rivers, wind, sea waves, and glaciers.
  • Mass movement: It refers to the movement of weathered material which is primarily because of gravity. E.g.: Landslide.
  • Erosion: Erosion is the carrying of broken rocks from one place to another by natural agents like wind, water, and glaciers.

WEATHERING
Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate. It is an in-situ (on-site) process. Climate is the main factor, also topography and vegetation.

There are three types of weathering processes:

1. Chemical weathering: It involves chemical decomposition of rocks and soil. Chemical weathering processes include dissolution, solution, carbonation, hydration, oxidation, and reduction that act on the rocks to decompose, dissolve or reduce them to a fine state.
   • Solution: Rainwater dissolves minerals which form weak acid and weather rock.
   • Oxidation: Reaction of O₂ in air or water with minerals in the rock. E.g.: iron in rocks start rusting.
   • Decomposition by Organic acid: Organic content in soil bacteria which form acid with water and help up weathering.
2. Physical/Mechanical weathering: Physical disintegration of rock. It works easily when the surface of the rock has already been weakened by the action of chemical weathering.
   • Repeated temperature change: Outer layer of rock expands when temperature increases and when temperature decreases it contracts more rapidly than the inner layer, creating stress.
   • Repeated wetting and drying: Stress is created by repeated wetting and drying. Wet surface expands outer layer and drying contracts outer layer which creates stress.
3. Biological weathering processes: Biological weathering is physical changes (removal of minerals and ions) due to growth or movement of organisms.
   • New surfaces for chemical attack are exposed by burrowing and wedging by organisms like earthworms, rodents, etc.
   • Human beings by disturbing vegetation, plowing, and cultivating soils.

Significance of Weathering

1. Geographic
   • Soil and Regolith: Weathering is a crucial base to our ecology as it converts bedrock into regolith and soil. Regolith is also notable for being the basic source for the inorganic part of soil.
   • Landforms: Differential weathering helps in the evolution of different types of landforms like stone lattice, tors, buttes, etc. Continuous removal and transfer of weathered materials through different processes of mass-translocation of rock wastes such as landslides and by the agent of erosion causes gradual lowering of the height of the affected area.

1. Economic
   • Resources: Weathering produces natural resources like clay, sand, gravel, etc. Practically all bauxite, most iron ore, and some copper ore are formed and concentrated by weathering.
   • Mining: Weathering weakens rocks making them easier for people to exploit, for example, by mining and quarrying.
   • Economic benefits: Weathering of rocks and deposits helps in the augmentation and concentrations of some valuable ores of manganese, aluminum, iron, and copper, etc., which have a great significance in the economy of the country.
   • Enrichment: Without weathering, the concentration of valuable materials may not be sufficient and economically viable to exploit, process, and refine. This is called enrichment.
2. Environmental
   • Help biodiversity: Biodiversity, and Biomes are basically a result of vegetation, and forests rely upon the depth of weathering mantles.
   • Increase concentration of minerals: When rocks undergo weathering, some materials are removed through chemical or physical leaching by groundwater and thereby the concentration of remaining (valuable) materials increases.
   • Disasters: In mountainous regions, mass wasting of weathered material on the slopes occurs in the form of landslides and debris avalanches leading to loss of life and property.