GEOMORPHIC PROCESSES 

 The earth’s crust is dynamic. The external forces of the earth are identified as ‘exogenic’; it reaction in the wearing down of relief or elevations and filling up of basins or depressions, on the earth's surface. The internal forces of the earth are identified as ‘endogenic’. Weathering, mass wasting, erosion, and deposition are the main exogenic processes.

1. Geomorphic processes

• The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing changes in the configuration on the surface of the earth are called geomorphic processes.
• Diastrophism and volcanism are endogenic geomorphic processes.
• Weathering, erosion and deposition are exogenic geomorphic processes.
• Any exogenic element of nature [Water, wind, ice etc.], capable of acquiring and transporting earth materials is known as a geomorphic agent.

1.1. Endogenic processes

• The energy emanating from within the earth is the main force behind endogenic geomorphic processes.
• This energy is mostly created by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.
• This energy is due to the geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere.
• Due to differences in geothermal gradients and heat flow from within, crustal thickness and strength, the action of endogenic forces is not uniform.
• Then the tectonically controlled original crustal surface is uneven.

Diastrophism

Diastrophism refers to the process of deformation or change in the Earth's crust due to tectonic forces, which can result in the formation of continents, mountains, valleys, and other geological features. It encompasses various processes such as folding, faulting, and volcanic activity, driven primarily by the movement of tectonic plates. These movements can create seismic activity, uplift mountains, alter landscapes, and influence the overall structure of the Earth's crust over long periods

All the 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.
• Epeirogenic processes involve the uplift or warping of large parts of the earth’s crust.
• Earthquakes involving local relatively minor movements.
• Plate tectonics involves horizontal movements of crustal plates.
• Orogeny is a mountain-building process.
• Epeirogeny is a continental building process.
• Volcanism includes the movement of magma towards the earth’s surface.

1.2. Exogenic processes

Exogenic processes are geological processes that primarily occur on or near the Earth's surface, driven by external forces such as weathering, erosion, transportation, and deposition. These processes reshape the Earth's surface by breaking down rocks, transporting sediments, and depositing them in new locations. They can be divided into several key categories:

1. Weathering: This is the breakdown of rocks and minerals at or near the Earth's surface due to various chemical, physical, and biological processes. It can be further classified into mechanical (physical) weathering and chemical weathering.
2. Erosion: Erosion is the process by which weathered materials (sediments, soil, rock fragments) are removed and transported from their original location by natural agents like water (rivers, streams), wind, ice (glaciers), or gravity (mass wasting).
3. Transportation: Once materials are eroded, they are transported by the agents of erosion. Water, wind, ice, or gravity move these sediments to new locations.
4. Deposition: Deposition occurs when eroded materials settle and accumulate in new areas, forming sedimentary layers. This sedimentation contributes to the formation of various landforms and geological features

2. Weathering

Weathering is the process through which rocks, minerals, and soils are broken down and disintegrated by various mechanisms. It's a fundamental part of the Earth's geological cycle and can be classified into two primary types: mechanical (physical) weathering and chemical weathering.

Mechanical (Physical) Weathering: This type of weathering involves the physical breakdown of rocks into smaller fragments without changing their chemical composition. Mechanical weathering processes include:

• • Frost Wedging: Water seeps into cracks in rocks, freezes, and expands, causing the cracks to widen and break the rock.

  • Exfoliation: This occurs when the outer layers of rocks expand and contract due to temperature changes, leading to the peeling or flaking of the rock layers.

  • Abrasion: Rocks break down as a result of rubbing or grinding against each other due to external forces like wind, water, or glaciers.

Chemical Weathering: Chemical weathering involves the alteration of rocks and minerals through chemical reactions. It changes the composition of the material. Common chemical weathering processes include:

• • Hydration: Minerals absorb water and expand, leading to physical changes in the structure of the rock.

  • Oxidation: Oxygen reacts with certain minerals, causing them to rust or change colour. Iron-rich minerals are especially prone to oxidation.

  • Dissolution: Minerals are dissolved by water, particularly those that are soluble in water, leading to the gradual disintegration of the rock

Temperature changes and expansion: Various minerals in rocks possess their own limits of expansion and contraction. Due to an increase in the temperature, the rocks may expand and if the temperature decreases rocks may contract. In rocks like Granites, smooth surfaced and rounded small to big boulders called ‘tors’ form due to such exfoliation.

Freezing, Thawing, and Forest Wedging: Forest weathering occurs due to the growth of ice within pores and cracks of rocks during repeated cycles of freezing and melting. This is most effective at high elevations in mid-latitudes, where freezing and melting are often repeated. Glacial areas are subject to frost wedging daily. Rapid freezing of water causes sudden expansion and high pressure.

Salt weathering: Salt in rocks expands due to thermal action, hydration and crystallisation. Many salts like calcium, sodium, magnesium, potassium and barium tend to expand. The expansion depends on the temperature and their thermal properties. The process of falling of individual grains may result in granular disintegration or granular foliation. With the salt crystal growth, chalk breaks down most readily, followed by lime stone, sandstone, shale, gneiss and granite etc.

Biological Activity and Weathering: It is the removal of minerals and ions from the weathering environment and physical changes due to the growth and movements of organisms. Burrowing and wedging organisms like earthworms, termites, rodents’ etc., Help in chemical attacks and penetration of moisture and air. Disturbing vegetation by ploughing and cultivating soils also helps in mixing and creating new contacts between air, water and minerals in the earth's materials. Plant roots exert tremendous pressure on the earth's materials mechanically breaking them apart.

Significance of Weathering

• It is responsible for breaking down the rocks into smaller fragments and preparing the way for the formation of regolith, soils, erosion and mass movements.
• Weathering is an important process in the formation of soils.
• Biomes and biodiversity results of forests depend on the depth of mantles.
• Weathering aids mass wasting, erosion and reduction relief and changes in the landforms are consequences of erosion.
• Weathering of rocks and deposits are enrichment and concentrations of iron ore, manganese, aluminium, copper etc.

3. Mass movements

These movements transfer the mass of the rock debris down the slopes under the direct influence of gravity. Debris may carry air, water or ice with it. These are very active over weathered slopes rather than over unweathered materials.

Several activating causes precede mass movements. They are

1. Removal of support from below to materials above through natural or artificial means.
2. Increase in gradient and height of slopes.
3. Overloading through the addition of materials natural or artificial filling.
4. Overloading due to heavy rainfall, saturation and lubrication of slope materials.
5. Removal of material or load from the over the original slope surfaces.
6. Occurrence of earthquakes, explosions or machinery.
7. Excessive natural seepage.
8. Heavy drawdown of water from lakes, reservoirs and rivers leads to slow outflow of water from under the slopes or river banks.
9. Indiscriminate removal of natural vegetation.

Heavy flow and slides are the three form movements, the relationship among different types of mass movements, their relative rates of movements and moisture limits.

1. Slow movements: Creep occurs on moderately steep, soil-covered slopes. Materials involved can be soil or rock debris. Soliflucation means downslope flowing soil mass or fine-grained. Grained rock debris saturated or lubricated with water. It is in moist temperature areas.
2. Rapid movements: Mostly prevalent in humid climatic regions and occurs over gentle to steep slopes. Earthflow is the movement of water-saturated clayey or silty earth materials down low-angle terraces or hillsides.

Mudflow: Mudflow is a flow of water that contains large amounts of suspended particles and silt. Mudflow occurs frequently in the on the erupted volcanoes. Volcanic ash, dust and other fragments are turned into mud due to heavy rains. Debris avalanches are similar to snow avalanches and occur in the Himalayas. It is faster than mudflow.

Landslides: A landslide is the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct influence of gravity.

A slump is the slipping of one or several units of rock debris with a backward rotation to the slope over which the movement takes place. Rapid rolling or sliding of earth debris without the backward rotation of mass is called debris slide. Sliding of individual rock masses down bedding, joint or fault surfaces is rockside.it is very fast and destructive.

Erosion and deposition: Though weathering aids erosion it is not a pre-condition for erosion to take place. The denudation processes like erosion and transportation are controlled by kinetic energy. If the rocks are permeable and soluble and water is available only then karst topography develops.

4. Soil formation

The soil formation depends upon the texture and structure as well as the minerals and chemical composition of the rocks or deposits. Soil is the result of decay and it is also the medium for growth. Pedology is soil science. Soil formation depends first on weathering.

Soil forming factors

There are five factors which control the formation of soil.

1. Parent material: It is a passive control factor in soil formation. it can be in-situ or on-site weathered rock debris.
2. Topography: It is like parental material is another passive control factor. In middle latitudes, the south-facing slopes exposed to sunlight have different conditions of vegetation and soils and the north-facing slopes with cool, moist conditions have some other soils and vegetation.
3. Climate: It is an important active factor in soil formation. Climatic elements involved in soil formation, Moisture interims of its intensity, frequency and duration of precipitation- evaporation and humidity and Temperature in terms of seasonal and diurnal variations. Precipitations maintain moisture in the soil for chemical and biological activities possible. Removal of silica from the soil is known as desilication. Due to high temperature water evaporates leaving salts in soil. Such soli that form into crust in the soil are called hardpans.
4. Biological activity: Biological activity in the soil is the amount of organic matter present.
5. Time: The length of the time the soil-forming process operates, determines, the maturation of soils and profile development. No specific length of time can be fixed for soils to develop and mature.