Endogenic & Exogenic Forces | Geography Optional for UPSC (Notes) PDF Download

Introduction

Geomorphology is the study of the earth's surface features and how they are shaped by various forces. These forces can be divided into two main categories: endogenic (internal) and exogenic (external). Together, these forces create the physical and chemical changes that shape the earth's landscape, and are referred to as geomorphic processes.

• Endogenic geomorphic processes, such as diastrophism and volcanism, occur within the earth's interior. Diastrophism encompasses the deformation of the earth's crust caused by tectonic forces, while volcanism includes the formation of volcanic landforms due to the eruption of molten materials.
• On the other hand, exogenic geomorphic processes take place on the earth's surface and include weathering, mass wasting, erosion, and deposition. Weathering is the breakdown of rocks and minerals by chemical and physical processes. Mass wasting refers to the movement of soil, rock, and other materials downslope under the influence of gravity. Erosion is the removal of earth materials by agents such as wind, water, ice, and gravity, while deposition is the accumulation of these materials in new locations.
• Geomorphic agents are the mobile mediums, like running water, moving ice masses, wind, waves, and currents, that facilitate the removal, transportation, and deposition of earth materials. These agents play a significant role in shaping the earth's surface through the various geomorphic processes.

Endogenic Forces

• The forces or movements within the Earth's crust are generated through the interaction of matter and temperature. These Earth movements can be broadly classified into two categories: diastrophism and sudden movements. The primary driving force behind these endogenic geomorphic processes is the energy that originates from within the Earth.
• This internal energy is primarily produced by radioactivity, rotational and tidal friction, as well as the primordial heat that has been present since the Earth's formation. Due to geothermal gradients and heat flow, this energy causes diastrophism (slow and gradual deformation of the Earth's crust) and volcanism (volcanic activity) within the lithosphere.

Diastrophism

• Diastrophism is the general term applied to slow bending, folding, warping, and fracturing.
  • Warp==make or become bent or twisted out of shape, make abnormal; distort.
• 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; In the process of orogeny, the crust is severely deformed into folds.
  • epeirogenic processes involving uplift or warping of large parts of the earth’s crust;
• Due to epeirogeny, there may be simple deformation. Orogeny is a mountain-building process whereas epeirogeny is a continental building process.
• Through the processes of orogeny, epeirogeny, earthquakes, and plate tectonics, there can be faulting and fracturing of the crust. All these processes cause pressure, volume, and temperature (PVT) changes which in turn induce metamorphism of rocks.

Diastrophism

Epeirogenic or Continent Forming Movements [Vertical Movements]

• Epeirogenic movement is a geological process that involves the gradual rising or sinking of large landmasses, such as continents, over extended periods of time. These movements exhibit long undulations or wavelengths and minimal folding in the earth's crust. Cratons, the stable and ancient central portions of continents, are particularly susceptible to epeirogeny.
• These epeirogenic movements are also referred to as radial movements since they act along the earth's radius. They can either cause the land to subside (move closer to the center of the earth) or uplift (move away from the center of the earth). The consequences of epeirogenic movements can often be observed in the geological features and landforms of affected areas.

Uplift

• Evidence of uplift can be seen in features such as raised beaches, elevated wave-cut terraces, sea caves, and fossiliferous beds found above sea level. In various locations along the coasts of Kathiawar, Nellore, and Thirunelveli, raised beaches can be found, with some elevated as much as 15 to 30 meters above the current sea level.
• There are also several instances where places that were once on the coast are now located inland. For example, Coringa, which is situated near the mouth of the Godavari River, Kaveripattinam in the Kaveri Delta, and Korkai on the Thirunelveli coast were all thriving seaports approximately 1,000 to 2,000 years ago. These areas have shifted inland due to the uplift process, demonstrating the changes that have taken place over time.

Subsidence

• Submerged forests, valleys, and buildings serve as evidence of land subsidence, which is the sinking of the earth's surface. An example of this occurred in 1819, when a section of the Rann of Kachchh was submerged due to an earthquake.
• The discovery of peat and lignite beds beneath sea level in Tirunelveli and the Sunderbans also indicates subsidence. In addition, the Andaman and Nicobar Islands have been separated from the Arakan coast as a result of the submersion of the land in between them.
• On the eastern side of Bombay island, trees have been discovered embedded in the mud approximately 4 meters below the low watermark. A similar submerged forest has been observed on the Thirunelveli coast in Tamil Nadu.
• A significant portion of the Gulf of Mannar and Palk Strait is shallow, indicating that it has been submerged in relatively recent geological times. Furthermore, part of the ancient town of Mahabalipuram, located near Chennai (formerly Madras), is now submerged in the sea.

Orogenic or the Mountain-Forming Movements [Horizontal Movements]

• Orogenic or the mountain-forming movements act tangentially to the earth’s surface, as in plate tectonics.
• Tensions produce fissures (since this type of force acts away from a point in two directions) and compression produces folds (because this type of force acts towards a point from two or more directions).
• In the landforms so produced, the structurally identifiable units are difficult to recognize.
• In general, diastrophic forces that have uplifted lands have predominated over forces that have lowered them.

Ocean-Continent Convergence

Sudden Movements

• Rapid changes in the Earth's surface, also known as sudden geomorphic movements, predominantly take place at the boundaries of lithospheric plates, or tectonic plate margins. These areas are highly unstable due to the immense pressure generated by the pushing and pulling of magma within the Earth's mantle, which is driven by convection currents. 
• As a result, these movements can cause significant alterations to the Earth's surface within a relatively short timeframe.

Earthquakes

• An earthquake occurs when the built-up stress in the Earth's interior rocks is released through weak zones on the planet's surface. This release of energy results in wave motions that cause vibrations, which can sometimes be devastating, on the Earth's surface. These movements can lead to various consequences, such as an uplift in coastal areas. For example, an earthquake in Chile in 1822 resulted in a one-meter rise in the coastal regions.
• Other effects of earthquakes may include alterations in land contours, changes in river courses, and the creation of tsunamis (seismic waves generated in the ocean by an earthquake, as they are known in Japan), which can lead to changes in shorelines. Additionally, earthquakes can trigger remarkable glacial surges (as observed in Alaska), landslides, soil creep, and mass wasting, among other phenomena.

Volcanoes

• Volcanism involves the movement of molten rock, known as magma, towards or onto the Earth's surface. It also includes the formation of various intrusive and extrusive volcanic forms. A volcano is created when magma from the Earth's interior escapes through vents and fissures in the crust, accompanied by steam, gases (such as hydrogen sulfide, sulfur dioxide, hydrogen chloride, carbon dioxide), and pyroclastic material. The shape of a volcano can vary depending on the chemical composition and viscosity of the lava.
• Pyroclastic flow is a dense, rapidly moving mixture of solidified lava pieces, volcanic ash, and hot gases, which occurs during certain volcanic eruptions. This flow is extremely hot and can incinerate anything in its path, potentially moving at speeds of up to 200 meters per second.

Exogenic (Exogenetic) Processes

• External forces, also known as exogenic forces, originate from outside the Earth's interior and primarily occur within its atmosphere. These forces are responsible for wearing down the Earth's surface, which is why they are referred to as land wearing forces.
• Exogenic processes are the result of stress applied to Earth's materials due to various forces that are generated by the heat from the sun. Stress, defined as the force applied per unit area, is created by pushing or pulling on a solid object.
• The development of stresses in Earth's materials ultimately leads to weathering, erosion, and deposition. Two key climatic factors that influence these processes are temperature and precipitation, as they play a significant role in inducing stress on Earth's materials.

Denudation

• All the exogenic geomorphic processes are covered under a general term, denudation.
• The word ‘denude’ means to strip off or to uncover.
• Weathering, mass wasting/movements, erosion, and transportation are included in denudation.
• Denudation mainly depends on rock type and its structure that includes folds, faults, orientation and inclination of beds, presence or absence of joints, bedding planes, hardness or softness of constituent minerals, chemical susceptibility of mineral constituents; permeability, or impermeability, etc.
• The effects of most of the exogenic geomorphic processes are small and slow but will, in the long run, affect the rocks severely due to continued fatigue.

Denudation: 4 Phases

1. Weathering
2. Erosion
3. Transportation
4. Deposition

Conclusion

Geomorphology is the scientific study of the Earth's surface features and the processes that shape them. Endogenic and exogenic forces play crucial roles in shaping the Earth's landscape through various geomorphic processes, such as diastrophism, volcanism, weathering, mass wasting, erosion, and deposition. Endogenic forces originate from within the Earth's interior and are responsible for slow and sudden movements, while exogenic forces are external processes that act on the Earth's surface and are largely influenced by temperature and precipitation. Together, these forces and the geomorphic agents contribute to the continuous transformation and evolution of the Earth's surface features through the complex process of denudation.

Frequently Asked Questions (FAQs) of Endogenic & Exogenic Forces

What is the main difference between endogenic and exogenic geomorphic processes?

Endogenic geomorphic processes occur within the Earth's interior and are driven by internal energy sources, such as radioactivity and geothermal heat. These processes include diastrophism and volcanism. Exogenic geomorphic processes occur on the Earth's surface and are driven by external forces, such as the sun's heat and precipitation. These processes include weathering, mass wasting, erosion, and deposition.

What are the primary driving forces behind endogenic geomorphic processes?

The primary driving forces behind endogenic geomorphic processes are the energy that originates from within the Earth, such as radioactivity, rotational and tidal friction, and the primordial heat that has been present since the Earth's formation.

What are some examples of epeirogenic movements, and how do they affect the Earth's surface?

Epeirogenic movements involve the gradual rising or sinking of large landmasses, such as continents, over extended periods of time. Examples of epeirogenic movements include uplift, which can cause raised beaches and elevated wave-cut terraces, and subsidence, which can lead to submerged forests, valleys, and buildings.

How do sudden movements, like earthquakes and volcanoes, impact the Earth's surface?

Sudden movements can cause significant alterations to the Earth's surface within a relatively short timeframe. Earthquakes can result in changes to land contours, alterations in river courses, and the creation of tsunamis, while volcanic eruptions can produce various intrusive and extrusive volcanic forms, as well as pyroclastic flows that can incinerate anything in their path.

What factors influence the rate and intensity of exogenic geomorphic processes?

Two key climatic factors that influence exogenic geomorphic processes are temperature and precipitation, as they play a significant role in inducing stress on Earth's materials. Additionally, factors such as rock type, structure, mineral composition, and permeability can also affect the rate and intensity of these processes.