Geomorphic Processes

• Geomorphic processes bring changes on the Earth’s surface
• Two types of geomorphic processes: exogenic and endogenic
• Endogenic processes: diastrophism and volcanism
• Exogenic processes: weathering, mass wasting, erosion, and deposition
• Geomorphic agent: mobile medium, e.g. running water, moving ice masses, wind, waves, and currents, etc.

Endogenic forces

• Endogenic forces originate inside the earth and are also called internal forces
• Internal forces lead to vertical and horizontal movements
• Result in subsidence, land upliftment, volcanism, faulting, folding, earthquakes, etc.
• Interaction of matter and temperature generates these forces/movements inside the earth’s crust
• Two types of earth movements: diastrophism (slow movements) and sudden movements
• Energy emanating from within the earth is the main force behind endogenic geomorphic processes
• Energy generated by radioactivity, rotational and tidal friction, and primordial heat
• Geothermal gradients and heat flow from within induce diastrophism and volcanism in the lithosphere.

Diastrophism

• Diastrophic forces created due to the motion of solid material on the earth’s surface
• Diastrophism is the term for slow bending, folding, warping, and fracturing of the earth’s crust
• All processes that move, elevate, or build up portions of the earth’s crust come under diastrophism
• Orogenic processes involve mountain building through severe folding and affecting long and narrow belts of the earth’s crust
• Epeirogenic processes involve uplift or warping of large parts of the earth’s crust
• Orogeny is a mountain-building process, while epeirogeny is a continental building process
• Through orogeny, epeirogeny, earthquakes, and plate tectonics, there can be faulting and fracturing of the crust
• These processes cause pressure, volume, and temperature (PVT) changes, inducing metamorphism of rocks.
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Epeirogenic or Continent forming movements [Vertical Movements]

• Epeirogenic movement refers to upheavals or depressions of land exhibiting long wavelengths and little folding
• Cratons, the broad central parts of continents, are subject to epeirogeny
• Epeirogenic movements act along the radius of the earth and are also called radial movements
• The direction of epeirogenic movements may be towards (subsidence) or away (uplift) from the center
• The results of epeirogenic movements may be clearly defined in the relief
• Uplift:
  • Raised beaches, elevated wave-cut terraces, sea caves, and fossiliferous beds above sea level are evidence of uplift
  • Raised beaches occur at several places along the Kathiawar, Nellore, and Thirunelveli coasts
  • Some raised beaches are elevated as much as 15 m to 30 m above the present sea level
  • Several places that were on the sea some centuries ago are now a few miles inland
  • Examples include Coringa near the mouth of the Godavari, Kaveripattinam in the Kaveri delta, and Korkai on the coast of Thirunelveli, all of which were flourishing seaports about 1,000 to 2,000 years ago.
• Subsidence:
  • Submerged forests and valleys, as well as buildings, are evidence of subsidence
  • In 1819, a part of the Rann of Kachchh was submerged as a result of an earthquake
  • Peat and lignite beds below sea level in Thirunelveli and the Sunderbans are examples of subsidence
  • The Andamans and Nicobars have been isolated from the Arakan coast due to submergence of the intervening land
  • Trees have been found embedded in the mud about 4 m below the low watermark on the east side of Bombay island
  • A similar submerged forest has also been noticed on the Thirunelveli coast in Tamil Nadu
  • A large part of the Gulf of Mannar and Palk Strait has been submerged in geologically recent times
  • Part of the former town of Mahabalipuram near Chennai (Madras) is submerged in the sea.

Orogenic or the mountain-forming movements [Horizontal Movements]

• Orogenic movements act tangentially to the earth’s surface
• Plate tectonics is an example of orogenic movement
• Tensions produce fissures and compression produces folds
• Structurally identifiable units are difficult to recognize in landforms produced by orogenic movements
• Diastrophic forces that uplifted lands have predominated over forces that lowered them.

Sudden Movements

• Sudden geomorphic movements occur at lithospheric plate margins (tectonic plate margins)
• These margins are unstable regions due to pressure created by magma pushing and pulling in the mantle (convectional currents)
• The movements cause considerable deformation over a short period of time

Earthquakes

• Earthquakes occur when surplus accumulated stress in rocks in the earth’s interior is relieved through weak zones over the earth’s surface causing vibrations on the earth’s surface.
• Earthquakes can cause uplift in coastal areas, changes in contours and river courses, tsunamis, glacial surges, landslides, soil creeps, and mass wasting.

Volcanoes

• Volcanism includes the movement of molten rock (magma) onto or toward the earth’s surface and also the formation of many intrusive and extrusive volcanic forms.
• A volcano is formed when the molten magma in the earth’s interior escapes through the crust by vents and fissures in the crust, accompanied by steam, gases, and pyroclastic material.
• Depending on the chemical composition and viscosity of the lava, a volcano may take various forms.
• A pyroclastic flow is a dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases that occurs as part of certain volcanic eruptions. It may move at speeds as high as 200 m/s.