Formation of The Himalayas UPSC Notes | EduRev

UPSC : Formation of The Himalayas UPSC Notes | EduRev

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Introduction

The origin of continents and oceans, the formation of mountains, the occurrence of earthquakes and eruption of volcanoes can be explained by Plate Tectonics. The credit for establishing this theory goes to Tuzo Wilson, who proposed the Wilson Cycle inspired from the works of the following geographers:

  • Harry Hess (1960)
  • R.S. Dietz (Global Tectonics 1961)
  • W.J. Morgan and Le Pichon (Seafloor spreading and Continental Drift 1968)

It is a theory of global dynamics in which the lithosphere is believed to be broken into a series of separate plates that move in response to convection currents in the upper mantle.

Plate is a broad segment of the lithosphere (including rigid upper mantle plus oceanic and continental crust) that is about 100km thick and floats on the underlying asthenosphere and moves independently of other plates.
The margins of the plates are sites of geological activity such as:

(1) Seafloor spreading
(2) Volcanic eruptions
(3) Earthquakes
(4) Crustal Deformation
(5) Mountain Building and
(6) Continental Drift

Formation of The Himalayas UPSC Notes | EduRev

Plate Interactions and Mechanism

Question 1:Which of the following is/are correct regarding the Aesthenosphere?
(1) It is the portion of the Earth's rigid crust and the upper solid portion of the mantle.
(2) It is the semi-molten layer which is a part of the upper mantle.
(3) It is the layer under pressure that lies between the mantle and the core
(4) The lithospheric plates move over the semi molten asthenosphere.
Choose the correct answer from the codes given below:

The Himalayas are the outcome of a convergence of the plate boundaries i.e,
Three types of plate boundaries:
(a) Constructive/ Diverging
(b) Destructive/ Converging
(c) Conservative/ Transform

  • Plates rip apart at a divergent plate boundary, causing volcanic activity and shallow earthquakes;
  • At a convergent plate boundary, one plate dives (“subducts”) beneath the other, resulting in a variety of earthquakes and a line of volcanoes on the overriding plate;
  • Transform plate boundaries are where plates slide laterally past one another, producing shallow earthquakes but little or no volcanic activity.

Formation of The Himalayas UPSC Notes | EduRev

Types of Plate Boundaries

The convergence of Eurasian plate in the north and Indian plate in the south. About 70 million years ago, the Indian plate started moving towards the Eurasian plate and the Tethys sea in between these two plates began to contract.
Formation of The Himalayas UPSC Notes | EduRev

Since the Indian plate was made up of denser material than the Eurasian plate, the former began to subduct under the latter causing lateral compression of the marine sediment in the bed of the Tethys. These sediments got folded in three successive phases giving rise to the ranges of the Himalayas.
Formation of The Himalayas UPSC Notes | EduRevOrigin of the HimalayasThe northward movement of the Indian plate still continues and hence the height of the Himalayan ranges continues to increase. The Indian plate still continues to move northward at the rate of 5 to 10 cm per year as a result of which one more fracture has appeared in the outer fringes of the Shivalik hills which demarcates these hills from the Northern plains of India.
It is anticipated that a new mountain chain would be formed in the Ganga basin forcing the rivers of this region to migrate further south. This indicates the process of the upheaval of the Himalayas is not yet over and will continue for a long period in the times to come.

Question 2:The Himalayas and the other fold mountains are the outcomes of :


Evidence to Prove That Himalayas Are Still Rising

  • Fossil formations and the climatic conditions of Shiwalik and Tibet Plateau were found to be similar.
  • Desiccation of the lakes of Tibet has been observed in recent or even in historical times. Surrounding these lakes, the sand and the gravel terraces at higher levels, sometimes 60-100m above the present water level, are seen which prove that the water stood at a much higher level until recently. This could be possible only in the event of uplift of the region.
  • The frequent instances of earthquakes in the Himalayan region prove that the Himalayas have not yet attained isostatic equilibrium and they continue to rise.
    Formation of The Himalayas UPSC Notes | EduRev

    Upliftment of the Himalayas

Isostatic Equilibrium - The state of gravitational equilibrium attained between Earth's crust and mantle depending on the thickness and density of the crust.

  • River terraces found at the valley sides suggest rejuvenation of the valley region due to uplift.

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