GEOMORPHIC PROCESSES
- Actions of exogenic forces result in wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/depressions, on earth’s surface.
- Phenomenon of wearing down of relief variations of surface of earth through erosion is known as gradation.
- Endogenic & exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes.
- Geomorphic agents are ground water, surface water, waves, currents ice, wind and gravity.
- Gravity besides being a directional force activating all downslope movements of matter also causes stresses on the earth’s materials.
EXOGENIC FORCES
- Derive their energy from two sources: a) Solar energy b) Gradient created by tectonic factors.
- Basic reason that leads to weathering, mass movements, and erosion is development of stresses in the body of the earth materials.
- Force applied per unit area is called stress.
- All the exogenic geomorphic processes are covered under a general term, denudation. The word ‘denude’ means to strip off or to uncover.
- Geomorphic processes depend upon multiple factors like a) structure of rocks (folds, faults, orientation and inclination of beds, presence of joints, hardness or of constituent minerals, permeability etc.), b)time and c)processes which operate on the rocks.
- These processes further depend upon various factors like latitude, season, land and
- water spread on the surface of the earth, density, type and distribution of vegetation, altitudinal differences, variation in the amount of insolation received, differences in wind velocities and directions, amount and kind of precipitation, evaporation, daily range of temperature, freezing and thawing frequency, depth of frost penetration etc.
WEATHERING
- Mechanical disintegration and chemical decomposition of rocks.
- It is an in-situ or on-site process.
Exfoliation – Flaking off more or less curved sheets of shells from over rocks or bedrock resulting in smooth and rounded surfaces. It is not the process but a result of weathering.
Exfoliation domes are created due to removal of the super incumbent load (unloading).
Exfoliated tors are created due to thermal expansion.
MASS MOVEMENTS
- Transfer the mass of rock debris down the slopes under the direct influence of gravity.
- Weathering is not a pre-requisite for mass movement though it aids mass movements. Mass movements are very active over weathered slopes rather than over unweathered materials.
- Air, water or ice do not carry debris with them from place to place but on the other hand the debris may carry with it air, water or ice.
MASS MOVEMENTS
- Transfer the mass of rock debris down the slopes under the direct influence of gravity.
- Weathering is not a pre-requisite for mass movement though it aids mass movements. Mass movements are very active over weathered slopes rather than over unweathered materials.
- Air, water or ice do not carry debris with them from place to place but on the other hand the debris may carry with it air, water or ice.
- Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves and currents participate in the process of mass movements.
- Heave: heaving up of soils due to frost growth and other causes, flow and slide are the three forms of movements.
- Landslides are relatively rapid and perceptible movements. The materials involved are relatively dry.
- Slump is slipping of one or several units of rock debris with a backward rotation with respect to the slope over which the movement takes place.
- Debris slide is rapid rolling or sliding of earth debris without backward rotation of Mass.
- Debris fall is nearly a free fall of earth debris from a vertical or overhanging face.
- Rockslide is sliding of individual rock masses down bedding, joint or fault surfaces.
- Solifluction is the flowage of water-saturated soil down a steep slope. Because permafrost is impermeable to water, soil overlying it may become oversaturated and slide downslope under the pull of gravity.
EROSION AND DEPOSITION
- It involves acquisition and transportation of rock debris which are formed because of weathering.
- Erosional geomorphic agents like running water, groundwater, glaciers, wind and waves remove and transport it to other places.
- Though weathering aids erosion it is not a pre-condition for erosion to take place.
- Deposition is a consequence of erosion. The erosional agents lose their velocity and hence energy on gentler slopes and the materials carried by them start to settle
- themselves.
- In other words, deposition is not actually the work of any agent. The coarser materials get deposited first and finer ones later.
- The same erosional agents viz., running water, glaciers, wind, waves and groundwater act as aggradational or depositional agents also.
EFFECT OF CLIMATE ON WEATHERING
- Rate of weathering: Humid climate increases the rate of weathering. High rain, humidity and heat break down the rocks faster.
- Type of weathering: Arid climate favour mechanical weathering whereas Humid climate favours chemical weathering. Biological weathering is also relatively higher in humid climate because of high vegetation and organisms in those areas.
- Types of rocks: Limestone weathers rapidly in areas with wet climates, where rainwater mixed with carbon dioxide in soil or creates a weak acid that dissolves the limestone to form crevices and valleys. Sandstone, by contrast, weathers more rapidly in dry climates, because the quartz in the sandstone is largely invulnerable to chemical weathering but can fall prey to fracturing caused by ice formed when water freezes and expands in cracks in the stone.
SIGNIFICANCE OF WEATHERING
Geomorphic significance: Break down the rocks and thus form the soils. Lead to various geomorphic processes like wasting and mass movements thus causing disasters like landslides.Weathering aids erosion and thus allow the development as well as evolution of various landforms.
Ecological significance: Biomes and biodiversity is basically a result of forests (vegetation) and forests depend upon the depth of weathering mantles.
Economic significance: Weathering of rocks and deposits helps in the enrichment and concentrations of certain valuable ores of iron, manganese, aluminium, copper etc., which are of great importance for the national economy.
