Geomorphic Processes

Geomorphic processes – Endogenetic & Exogenetic Forces – UPSC Geography Notes

Geomorphic processes result from endogenic and exogenic factors, inducing physical stress and chemical reactions in Earth’s substances, leading to changes in surface configuration.

  • Endogenic processes include diastrophism and volcanism; exogenic processes include weathering, mass wasting, erosion, and deposition.
  • Exogenic materials act as geomorphic agents, facilitating the transfer of Earth materials via gradients, causing their removal, transportation across slopes, and deposition at lower levels.
  • Movements occur from higher to lower levels or from high to low-pressure zones, driven by gradients.
  • Geomorphic agents include groundwater, glaciers, winds, waves, currents, and running water.
  • Gravitational stresses play a significant role, as gravity is responsible for Earth’s material movement, enabling erosion, transportation, and deposition.

What are Geomorphic Agents?

  • Geomorphic agents are natural forces shaping the Earth’s surface through erosion, transportation, and deposition processes.
  • They sculpt landscapes, contributing to the continual transformation and renewal of the Earth’s topography.
  • Examples of geomorphic agents include running water, groundwater, glaciers, wind, waves, and currents.
  • Each agent operates uniquely, influenced by factors such as climate, topography, underlying geology, and vegetation.

Types of Geomorphic Process

Endogenic Forces

  • Endogenic forces rely on the Earth’s internal energy and play a pivotal role in shaping the Earth’s crust.
  • Examples include mountain-building forces, continent-building forces, earthquakes, and volcanic activities.
  • These forces primarily serve as land-building agents, contributing to the formation of the Earth’s surface.
  • The energy powering endogenic geomorphic processes originates from sources such as radioactivity, rotational and tidal friction, and primordial heat from the Earth’s origin.

Slow Movements (Diastrophic forces)

Diastrophic forces pertain to the forces resulting from the movement of the Earth’s crustal material. Diastrophism encompasses all processes that cause movement, uplift, or construction of segments of the Earth’s crust. It can be classified into several types, including:

  • Orogenic processes, which contribute to mountain building through extensive folding, impacting elongated and narrow belts of the Earth’s crust.
  • Epeirogenic processes, which lead to the uplift or warping of significant sections of the Earth’s crust.
  • Earthquakes, which involve localized and relatively minor movements.
  • Plate tectonics, which involve the horizontal movements of crustal plates.
  • Slow movements that can be categorized into vertical and horizontal movements.
Vertical Movements (Epeirogenic movements)
  • Vertical movements, also known as Epeirogenic movements, contribute to the formation of continents and plateaus.
  • The central parts of continents, known as cratons, are subject to epeirogeny.
  • These movements do not affect the horizontal rock strata.
  • While they lead to the uplift of continents, they can also result in the subsidence of continents.
  • Epeirogenic movements originate from the Earth’s core.
Horizontal Movements (Orogenic Movements)
  • Horizontal forces operate on the Earth’s crust sideways, causing these movements.
  • Also known as orogenic movements (mountain building), they induce significant disturbances to the horizontal layers of strata, leading to substantial structural deformations of the Earth’s crust.
  • These forces can be classified as either forces of compression or forces of tension.
Forces of Compression
  • Forces of compression push rock strata against a solid plane from one or both sides.
  • These compressional forces cause the bending of rock layers, leading to the formation of Fold Mountains.
  • Major mountain chains like the Himalayas, the Rockies in North America, the Andes in South America, and the Alps in Europe are the result of these compressional forces.
Forces of Tension
  • Tension forces act horizontally but in opposite directions.
  • Intense tensional forces cause rock strata to fracture, leading to the development of cracks and fissures in the Earth’s crust.
  • Faulting occurs when rock displaces upward or downward from its original position along such fractures, known as fault lines.
  • Faulting contributes to the formation of recognizable topographical features such as Rift Valleys and Block Mountains, for example, the Vindhya and Satpura Mountains.
  • Rift valleys form as a result of the subsidence of rock strata between two almost parallel faults, seen in examples such as the Valley of the Nile and the Narmada and Tapti Rift valleys.
  • Rift valleys characterized by steep parallel walls along faults are termed Graben, while uplifted landmasses with steep slopes on both sides are known as Horst.
  • A continuous line of very steep slope along a fault is referred to as an Escarpment.

Sudden Movements

  • The lithospheric plate boundaries are vulnerable to sudden geomorphic movements.
  • Instability at these boundaries arises from the pressure generated by the pushing and pulling of magma in the mantle.
  • Earthquakes and volcanoes serve as prime examples of sudden movements that can swiftly lead to significant deformations.

Exogenic Forces

  • Exogenic forces derive their strength from the Earth’s exterior or within the Earth’s atmosphere, influencing surface processes.
  • Examples include the wind, waves, and water, contributing to weathering, mass movement, erosion, and deposition.
  • Exogenic forces primarily act as land-wearing agents, leading to the degradation of relief or elevations and the filling up of basins or depressions on the Earth’s surface.
  • Weathering involves the breakdown of rocks by agents such as rivers, wind, sea waves, and glaciers, while erosion entails the transportation of fragmented rocks by wind, water, and glaciers.
  • The cumulative impact of exogenic forces results in the gradual wearing down of surface relief variations, a process known as gradation.

Weathering

Weathering refers to the breakdown and decomposition of rocks through the influence of diverse weather and climatic elements. This process primarily occurs in the same location without significant material movement, known as in-situ or on-site weathering.

Three distinct types of weathering processes exist: physical weathering, chemical weathering, and biological weathering.

Physical Weathering

Physical or mechanical weathering refers to the breakdown of rocks primarily caused by various weather elements. It is triggered by changes in pressure, temperature, wind, and water. This type of weathering is further categorized into thermal weathering, frost weathering, and exfoliation.

Thermal weathering: In arid and semi-arid regions, high daytime temperatures cause rocks to expand, while they contract at night as temperatures drop. The drastic temperature shifts lead to the cracking and splitting of rocks. Thermal weathering can be classified into granular disintegration and block disintegration.

  • Granular disintegration: Mineral expansion and contraction due to temperature variations result in the breakdown of rocks into small pieces, causing gradual fragmentation.
  • Block disintegration: Intense temperature fluctuations cause rocks, such as granite, to break along joints, forming large rectangular blocks.

Frost wedging: Water that freezes within rock cracks expands, exerting pressure that deepens and widens the cracks.

Exfoliation: Surface layers of rocks heat or cool more rapidly, causing them to peel off from the main rock mass in concentric layers, resembling the peeling of an onion. This process creates dome-shaped monoliths and is prominent in arid regions, also known as onion weathering.

Chemical Weathering

Several weathering processes, such as solution formation, oxidation, reduction, carbonation, and hydration, act on rocks, leading to their disintegration, decomposition, and dissolution into finer states. Water, oxygen, carbon dioxide, and temperature presence accelerate these chemical reactions. The various types of chemical weathering include:

  • Solution: Water dissolves soluble minerals in rocks over extended periods, gradually washing away these minerals, sometimes leading to the formation of caves.
  • Hydrolysis: Rock materials undergo chemical breakdown upon contact with water, forming insoluble precipitates such as clay minerals. For example, the hydrolysis of feldspar in granite changes it into clay.
  • Carbonation: Water reacting with carbon dioxide leads to the formation of carbonic acid, which in turn reacts with minerals in the rocks. This reaction plays a crucial role in the creation of caves.
  • Oxidation: The combination of oxygen with water and iron weakens rocks, causing them to disintegrate. For instance, the rusting of iron is a familiar example of oxidation in rocks.
  • Hydration: The absorption of water causes a volume expansion, resulting in the deformation of rocks. For example, anhydrite (CaSO₄) absorbing water transforms into gypsum (CaSO₄.2H₂O).
Biological Weathering

Biological weathering refers to the modification of rock through the influence of plants, animals, and human activities. Organisms such as termites, rodents, and earthworms contribute to the exposure of rock surfaces to chemical changes through burrowing and wedging, allowing moisture and air to penetrate. Human activities such as deforestation, soil cultivation, and disturbance of vegetation create new interactions between water, air, and minerals in the Earth’s materials. Decomposition of organic matter by plants and animals results in the production of various acids, including humic and carbonic acids, heightening the decomposition and solubility of certain elements. Additionally, the pressure exerted by plant roots on Earth materials aids in the fragmentation of rocks.

Importance of Weathering
  • Weathering processes contribute to the formation of regolith and soils.
  • They prepare the soil for erosion and mass movements.
  • Certain materials are removed through physical or chemical leaching by groundwater, increasing the concentration of remaining valuable materials.
  • This process, known as enrichment, aids in raising the concentration of specific valuable ores such as copper, aluminum, and iron.

Mass Movements

These movements involve the transfer of rock debris down slopes, primarily influenced by the force of gravity. The debris may be accompanied by water, air, or ice, and this process is referred to as mass wasting. Mass movements can occur either abruptly or gradually. While weathering can facilitate mass movements, it is not a mandatory precursor for such events. Factors such as weak unconsolidated materials, faults, thinly bedded rocks, steeply dipping beds, steep slopes or vertical cliffs, abundant precipitation, heavy rainfall, and sparse vegetation all contribute to mass movements.

Types of Mass Movements
  • Rock falls: Free-falling of rock blocks down a steep slope from the superficial layers of a rock face. Accumulation of rock debris at the slope base is known as talus.
  • Rock slides: Follow zones of weakness, with increased slippage in the presence of water. Collisions down the slope break rock masses into rubble, affecting materials to a substantial depth.
  • Landslides: Large rock pieces break off and slide down hills, often triggered by earthquakes or heavy rain.
  • Slump: A great mass of bedrock moves downward by rotational slip from a high cliff. Slumping is typically caused by erosion at the slope base, reducing support for overlying sediments.
  • Debris slide: Occurs on a larger scale, involving a mixture of soil and rock fragments.
  • Debris flow: Includes mudflows, earth flows, and debris avalanches. Turbulence occurs throughout the mass, usually caused by loss of cohesion due to a significant water presence. Large boulders carried by debris flows can be highly destructive.
    • Earth flow: Earth material moving down a hill as a fluid-like mass, often in humid regions on steep slopes with clay-rich soil saturated during storms.
    • Mudflow: A swift-moving liquid mass of soil, rock debris, and water moving down a well-defined channel, common in mountainous semi-arid environments. A mudflow from a volcanic slope is termed a lahar.
    • Debris avalanche: A rapidly churning mass of rock debris, soil, air, and water swiftly moving down steep slopes, with air acting as a cushion to increase speed.
  • Creep: Slow, gradual downhill movement of soil, often less than a centimeter per year. Soil creep is aided by freezing and thawing, progressively moving soil particles downhill.

Erosion and Deposition

  • Erosion involves the acquisition and transport of rock debris, alongside weathering and mass wasting, as a degradational process.
  • Erosive agents, including wind, running water, glaciers, waves, and groundwater, are responsible for erosion, with wind, running water, and glaciers influenced by climatic conditions.
  • Wave activity relies on coastal location, while groundwater effects are predominantly determined by the lithological character of the region.
  • Erosion leads to the degradation of relief and is a significant factor in the continuous changes observed on the Earth’s surface, controlled by kinetic energy.
  • Erosional agents lose velocity and energy on gentler slopes, leading to the settling and deposition of materials, with coarser materials deposited before finer ones.
  • The same geomorphic agents responsible for erosion also function as depositional or aggradational agents, with depositions filling up depressions in the landscape.
Soil Formation (Pedogenesis)

Soil formation, or pedogenesis, primarily relies on weathering, with the depth of the weathered material (weathering mantle) serving as the fundamental source for soil development. Initially, the weathered material or transported deposits become home to bacteria, lichens, mosses, and various other small plant entities. The mantle and deposits also provide shelter to numerous microorganisms. The organic remains of plants and organisms contribute to the creation of humus.

Minor grasses and ferns may grow initially, followed by the establishment of shrubs and trees through seeds dispersed by wind and birds. Plant roots penetrate downwards, while burrowing animals bring up particles, leading to the development of a porous mass capable of retaining water and facilitating air passage. Ultimately, a mature soil, comprising a complex amalgamation of mineral and organic components, takes shape.

Soil forming factors – The following five factors control the formation of soil;

  • Parent material
  • Topography
  • Climate
  • Biological activity
  • Time

The relative influence of these factors varies across different locations, but typically, the collective impact of all these different elements determines the type of soil that develops in any particular area.

Parent material

The materials from which soils are derived can be either in-situ weathered rock debris, known as residual soils, or transported deposits, referred to as transported soils. The process of soil development is influenced by factors such as the size of the debris, its structure, and the chemical composition of the rock remnants or deposits. While younger soils are closely tied to the type of parent rock, with age, exposure to moisture, the addition of organic matter, and other environmental elements can alter their characteristics.

Topography

The topography, including relief, altitude, and slope, plays a significant role in shaping soil properties. On steep slopes, the soil tends to be thinner due to rapid water runoff, leading to surface erosion. Furthermore, direct sunlight exposure on slopes can accelerate the drying out of soil moisture, reducing its fertility. In contrast, on gentle slopes where erosion is gradual and water percolation is efficient, the conditions for soil formation are highly favorable. Flat areas facilitate the development of a thick layer of clay and promote the accumulation of organic matter, resulting in the characteristic dark color of the soil.

Climate

Among the significant factors contributing to soil formation, climate holds a crucial position. Two vital components of the climate, namely precipitation and temperature, actively participate in the process of soil development.

  • Precipitation – Moisture content, facilitated by precipitation, is pivotal for enabling chemical and biological activities within the soil. Excessive water leads to the movement of soil components through eluviation, with subsequent deposition below the surface, known as illuviation. Regions with abundant rainfall often experience the depletion of essential elements such as sodium, potassium, magnesium, calcium, and a significant portion of silica from the soil. The removal of silica from the soil is termed as desilication. Conversely, arid climates lead to higher evaporation than precipitation, resulting in salt-rich soils, often forming a hardened layer known as hardpans. Tropical climates and areas with moderate rainfall give rise to the formation of calcium carbonate nodules, commonly referred to as kankers.
  • Temperature – Higher temperatures stimulate chemical activities, while cooler temperatures tend to inhibit them (with the exception of carbonation), and freezing conditions altogether halt these activities. Consequently, tropical soils, characterized by higher temperatures, exhibit deeper soil profiles. In frozen tundra regions, the soil primarily comprises mechanically fragmented materials due to the freezing conditions.
Biological Processes

Within the realm of soil formation, the presence of vegetation and various organisms plays a crucial role in incorporating organic matter, enhancing moisture retention, and contributing nitrogen content. Deceased plant matter enriches the soil with humus, a finely divided organic substance. During the process of humification, certain organic acids are generated, aiding in the decomposition of minerals found in the original soil materials.

  • The level of biological activity in the soil is contingent upon the climate of the specific region. In colder climates, the accumulation of humus is prominent, given the sluggish bacterial growth. The slow bacterial activity leads to the buildup of layers of peat in sub-arctic and tundra climates, characterized by undecomposed organic matter. Conversely, in humid tropical and equatorial climates, rapid bacterial activity leads to the swift oxidation of deceased vegetation, resulting in significantly low humus content in the soil.
  • Certain bacteria, such as rhizobium, play a beneficial role by fixing nitrogen for their host plants. The conversion of atmospheric nitrogen into ammonia or related nitrogenous compounds is known as nitrogen fixation. Additionally, the activities of ants, termites, earthworms, rodents, and similar creatures are instrumental in the process of soil formation as they facilitate the mixing of soil layers through their burrowing activities.
Time

A soil reaches full maturity as a result of prolonged engagement of various soil-forming processes, allowing for the development of a comprehensive profile. Alluvium that has been recently deposited is categorized as young, typically lacking well-developed or any discernible horizons.

FAQs

Q: What are exogenic geomorphic processes?

A: Exogenic geomorphic processes are those processes that occur on the Earth’s surface and are primarily driven by external forces like weathering, erosion, and deposition.

Q: What are some examples of exogenic geomorphic processes?

A: Examples include wind erosion, water erosion, mass wasting, glacial erosion, and coastal erosion.

Q: How do endogenic geomorphic processes influence the Earth’s surface?

A: They contribute to the formation of landforms such as mountains, plateaus, rift valleys, and volcanic landforms.

Q: What is the difference between endogenic and exogenic geomorphic processes?

A: Endogenic processes originate from within the Earth and are responsible for the movement of the Earth’s crust, while exogenic processes are driven by external forces acting on the Earth’s surface.

Q: How do endogenic and exogenic processes interact?

A: They often work together to shape the Earth’s surface, with endogenic processes creating landforms that are further modified by exogenic processes.

Q: What are the important points to remember about endogenic and exogenic geomorphic processes for the UPSC exam?

A: Focus on understanding the key differences between endogenic and exogenic processes, their impact on landform development, and their role in shaping the Earth’s surface. Also, be familiar with specific examples and case studies that highlight the interaction between these processes.

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