Endogenetic and Exogenetic forces

I. EXOGENETIC FORCES

Also Known as: Denudation

What is Exogenetic Forces?

Exogenetic forces refer to the natural processes that result in the lowering and leveling out of the Earth’s surface.

How do Exogenetic Forces Work?

Exogenetic forces encompass various processes that contribute to the transformation of the Earth’s surface. These processes include weathering, erosion, transportation, deposition, mass wasting, and mass movement.

Weathering

• Definition: Weathering is the disintegration of rocks in their original location, without involving any significant motion of the disintegrated rocks.
• Features: The rate and type of weathering depend on the structure of the rock, climatic conditions, degree of slope, and biotic factors.
• Types of Weathering:
  1. Physical weathering: This type of weathering involves the disintegration of rocks due to changes in temperature, frost action, and the mechanical force of wind and water.
     • Ways of Physical Weathering: a. Block disintegration: Occurs in areas with a high daily range of temperature and when water repeatedly enters cracks in rocks, causing expansion and contraction. b. Granular disintegration: If water fills up the pore space of rocks and undergoes freeze-thaw action, rocks disintegrate into smaller pieces. c. Disintegration due to unloading: When the overlying load is removed, rocks start expanding, resulting in phenomena such as sheeting, spalling, and cambering.
  2. Chemical weathering: Chemical weathering occurs in areas with abundant moisture and involves the dissolution and alteration of rocks through various chemical processes.
     • Processes of Chemical Weathering: a. Carbonation: Water in the presence of carbon dioxide forms a weak acid that dissolves rocks like limestone and dolomite. b. Solution: Some minerals or salts dissolve in water and are transported in solution. c. Hydration: Certain minerals absorb water, leading to an increase in volume, which causes repeated wetting and drying and the development of cracks known as flaking. d. Chelation: This process occurs in the presence of leaves that secrete acids, which translocate ions in minerals to the subsoil, common in coniferous leaves. e. Oxidation: Reaction of oxygen in air or water with minerals produces oxides that weaken rocks and contribute to their disintegration, such as iron oxide causing rusting. f. Hydrolysis: Chemical reaction between minerals, water, hydrogen ions, and hydroxyl ions results in the breakdown of minerals.
  3. Biochemical weathering: Biochemical weathering involves the disintegration and decomposition of rocks due to organic materials from both fauna (animals) and flora (plants).
     • Examples of Biochemical Weathering: a. Humic acids: Activate processes like chelation and aid in the decomposition of silicate minerals. b. Bacterial acids: Various acids produced by bacteria, such as lactic acid, acetic acid, and gluconic acid, contribute to weathering. c. Microfaunal acids: Acids produced by microfauna weather silicate minerals and clays, including oxalic acid and citric acid.

Erosion

Erosion refers to the removal of weathered material, leading to the lowering of the Earth’s surface. It occurs mainly through ex-situ processes.

Transportation

Transportation involves the movement of weathered material to a new destination through various agents such as water, wind, or ice.

Deposition

Deposition occurs when the eroded material is placed at a particular point, leading to the formation of landforms such as depositional plains, sand dunes, and glacial till.

Mass Wasting

Mass wasting refers to the downward movement of unconsolidated rock or regolith under the influence of gravity, water, slope steepness, removal of vegetation cover, or earth tremors.

Mass Movement

Mass movement involves the detachment and downhill movement of soil and rock under the influence of gravity. It can be classified based on water requirement.

• Very Rapid Movement:
  • Landslides:
    • Slump: Intermittent sliding of rock fragments along a curved plane caused by rotational movement or displaced blocks. It covers a short distance.
    • Slides: Downhill movement of weathered material along discrete shear surfaces.
    • Fall: Instantaneous fall of weathered rock material, including large boulders, under the influence of gravity.
  • Examples: Rock slump, debris slump, rock slides, debris slides.
• Slow Movement:
  • Creep: Very slow and imperceptible downslope movement of material.
    • Examples: Soil creep (movement of moistened soils down slope) and rock creep (movement of rock upon rock).
• Rapid Movement:
  • Flow: Diagonal downslope movement of rock fragments and soil along a sliding plane with sufficient water.
  • Examples: Earth flow, mudflow, debris flow.
• Sheet Wash: The removal of thin layers of surface soil by running water.

II. Endogenetic Forces

Endogenetic forces are those that originate from within the earth. They are responsible for two primary types of movements: horizontal movements and vertical movements. This comprehensive exploration delves into the definition, classification, and resulting landforms of endogenetic forces.

Classification of Endogenetic Forces

There are primarily three types of endogenetic forces, classified as Diastrophic Forces, and Sudden Forces or Constructive Forces.

Diastrophic Forces

Diastrophic Forces originate from the forces deep within the earth and operate very slowly. Owing to their slow movement, these forces are also termed constructive forces.

Within this classification, there are two significant groups of forces: Epeirogenetic forces and Orogenetic forces.

Epeirogenetic Forces get their name from “Epiros,” which means continents, and “Genesis,” which translates to origin. There are two types of Epeirogenetic forces:

• Upward Movement (Emergence) causes the upliftment of a continent in two specific ways: the upliftment of the whole or a part of the continent and the upliftment of the coastal land of the continent.
• Downward Movement (Submergence) is marked by the subsidence of continental masses in two ways: the subsidence of the land area (also known as subsidence) and the submergence of the land area under seawater (also known as submergence).

Orogenetic Forces, on the other hand, derive their name from “Oros,” which means mountain, and “Genesis,” which implies origin or formation. These forces are triggered by endogenetic forces working in a horizontal manner and are often referred to as Tangential Forces. There are two types of Orogenetic forces:

• Forces that operate in the opposite direction are called Tensional or Divergent Forces. They lead to crustal fractures through processes such as cracking and faulting. Different terms associated with these processes include:
  • Fault plane: The plane along which rock planes are displaced by tensional or compressional forces.
  • Fault dip: The angle between the fault plane and the horizontal plane.
  • Upthrown side: The uppermost block of a fault.
  • Downthrown side: The lowermost block of a fault.
  • Hanging wall: The upper wall of a fault.
  • Foot wall: The lower wall of a fault.
  • Fault scrap: The steep wall-like slope caused by faulting of crustal rocks.
• Forces that operate face to face are known as Compressional or Convergent Forces. They lead to crustal bending and warping, which results in the formation of folds and other structures.

Sudden Forces or Constructive Forces

Sudden Forces or Constructive Forces are characterized by sudden movement due to endogenetic forces coming from deep within the earth. These forces are considered constructive because they create specific relief features on the earth’s surface, such as volcanic mountains and extensive lava plateaus due to volcanic eruptions, and faults, fractures, and lakes due to earthquakes.

These sudden movements often lead to substantial destruction at and below the earth’s surfaces, earning them the label of “extreme events.”

Landforms caused by Endogenetic Forces

The activity of endogenetic forces results in the creation of several different landforms. Some notable examples are valleys, trenches, and geosynclines.

Valleys are elongated and structural depressions caused by internal forces and erosion. A prime example of a valley is the Rift Valley or Graben.

Trenches are enormous depressions or gaps in the earth’s crust, formed where the ocean crust sinks into the mantle, a process known as subduction. They are always underwater and are often associated with violent earthquakes and explosive volcanic eruptions. Examples of trenches include the Mariana Trench, Chile-Peru Trench, Japan Trench, Mexican Trench, and the Sunda-Java Trench.

Geosynclines are a downward bend of rock. The Mediterranean Sea and the Tethys Sea (an ancient geosyncline) are examples of geosynclines.

The study of endogenetic forces and their influence on the formation and transformation of the earth’s surface is pivotal to understanding the dynamic nature of our planet. These forces, operating deep within the earth, continually shape and reshape the landscapes around us in subtle and dramatic ways.