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Second Order Relief

Earth’s crust and its surface are constantly evolving (changing) due to various forces emanating from....Second Order Relief

Earth’s crust and its surface are constantly evolving (changing) due to various forces emanating from below (endogenic forces) as well as above the surface of the earth (exogenic forces).These forces cause physical and chemical changes to the geomorphic structure (earth’s surface). Some of these changes are imperceptibly slow (e.g. weathering, folding), some others are gradual (e.g. erosion) while the remaining are quite sudden (earthquakes, volcanic eruptions).

Endogenic processes:

The forces originating from deep below the Earth’s surface give rise to large-scale movements on the Earth’s crust or its surface. These movements are referred to as endogenic geomorphic movements or simply endogenic movements. (endo: internal; genic: origin; geo: earth; morphic: form).

The forces originating from deep below the Earth’s surface drive geomorphic processes known as endogenic geomorphic processes (such as folding, faulting, etc.).

Endogenic processes are divided into diastrophic process and sudden process.

  • Diastrophism refers to deformation of the Earth’s crust.
  • Diastrophic movements are gradual and might stretch for thousands of years.
  • Diastrophic processes are further classified into epeirogenic processes (continent forming ― subsidence, upliftment)and orogenic processes (mountain building ― folding, faulting).
  • On the other hand, sudden processes like earthquakes and volcanic eruptions occur in a very short period.

Eperiogenic processes:

Epeirogenic movement refers to upheavals or depressions of land exhibiting long wavelengths [undulations] and little folding.

The broad central parts of continents, known as cratons, are affected by epeirogeny. Radial movements, also known as epeirogenic or continent-forming movements, exert their action along the radius of the Earth. These movements can be categorizes as subsidence, where the direction is towards the center, or uplift, where the direction is away from the center. The relief clearly displays the outcomes of these movements.

  • Raised beaches, elevated wave-cut terraces, sea caves and fossiliferous beds above sea level are evidences of uplift.
  • Raised beaches, some of them elevated as much as 15 m to 30 m above the present sea level, occur at several places along the Kathiawar, Nellore, and Thirunelveli coasts.
  • Several places which were on the sea some centuries ago are now a few miles inland.
  • For example, Coringa near the mouth of the Godavari, Kaveripattinam in the Kaveri delta and Korkai on the coast of Thirunelveliwere all flourishing seaports about 1,000 to 2,000 years ago.
  • Submerged forests and valleys, as well as buildings, are evidences of subsidence.
  • In 1819, a part of the Rann of Kachchh was submerged as a result of an earthquake.
  • The presence of peat and lignitebeds below the sea level in Thirunelveli and the Sunderbans is an example of subsidence.
  • The Andamans and Nicobarshave been isolated from the Arakan coast by the submergence of the
    intervening land.
  • Embedded in the mud about 4 meters below the low watermark, researchers have discovered trees on the east side of Bombay island. A similar submerge forest has also noticed on the Thirunelveli coast in Tamil Nadu.
  • Geologically recent times have witnessed the submergence of a significant portion of the Gulf of Mannar and Palk Strait, rendering them very shallow. The sea has engulfed a section of the former town of Mahabalipuram near Chennai (Madras).

Orogenic processes:

When two tectonic plates collide, they initiate the process of mountain building, which is known as orogenesis. This collision forces the material upwards, forming mountain belts such as the Alps or Himalayas, or it causes one plate to subduct below the other, resulting in the formation of volcanic mountain chains like the Andes.

  • In contrast to epeirogenic movement, the orogenic movement is a more complicated deformation of the Earth’s crust, associated with crustal thickening (due to the convergence of tectonic plates).
  • Such plate convergence forms orogenic belts that are characterized by “the folding and faulting of layers of rock, by the intrusion of magma, and by volcanism.
  • Orogenic or mountain-forming movements act tangentially to the earth’s surface, as in plate tectonics.
  • Tension produces 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).

Second order relief features

  • The result of plate collision or divergence.
  • Rifts form where plates diverge from one another.
  • If parallel rifting occurs, rift valleys, like the Great Rift Valley of Africa can form.
  • Rifting can be accompanied by volcanic activity as magma pours out of the rift.
  • Mt. Kilimanjaro was formed as a result of the rifting that created the Great Rift Valley of Africa.

Great mountain systems or trenches are creats when plates converge. When two continental plates collide it causes the Earth to fold and buckle. Such is the case when the Indian Plate collided with the Eurasian Plate creating the Himalaya Mountains.

Second Order Relief,Second Order Relief,Second Order Relief

Read Also : Classification Of Plateaus

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