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Ch-2 | Physical Features of India | NCERT Class 9

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SUMMARY

  • Our country has practically all major physical features of the earth i.e. mountains, plains, deserts, plateaus and islands
  • India is a large landmass formed during different geological periods which has influenced her relief.
  • Besides geological formations, a number of processes such as weathering, erosion, and deposition have created and modified the relief to its present form.

THEORY OF PLATE TECTONICS

  • Earth scientists have attempted to explain the formation of physical features with the help of some theories based on certain evidence. One such plausible theory is the “Theory of Plate Tectonics”.
  • According to this theory, the crust (upper part) of the earth has been formed out of seven major and some minor plates.
  • The movement of the plates results in the building up of stresses within the plates and the continental rocks above, leading to folding, faulting, and volcanic activity.
  • Broadly, these plate movements are classified into three types:
    1. Convergent: When Plate Boundaries come towards each other.
    2. Divergent: When Plate Boundaries move away from each other.
    3. Transform: When Plate Boundaries move horizontally past each other (Rubbing / Friction).

  • These Plate Movements have resulted in the formation of various landforms such as Volcanoes, Young Fold Mountains, Block Mountains, Rift Valleys etc.

Plate Boundaries of the Earth

GONDWANA LAND to FORMATION OF HIMALAYAS + PLAINS

  • The oldest landmass, (the Peninsula part), was a part of the Gondwana land.
  • The Gondwana land included India, Australia, South Africa, South America and Antarctica as one single land mass.
  • The convectional currents split the crust into a number of pieces, thus leading to the drifting of the Indo-Australian plate after being separated from the Gondwana land, towards the north.
  • The northward drift resulted in the collision of the plate with the much larger Eurasian Plate.
  • Due to this collision, the sedimentary rocks which were accumulated in the geosyncline known as the Tethys were folded to form the mountain system of western Asia and Himalaya.
  • The Himalayan uplift out of the Tethys sea and subsidence of the northern flank of the peninsular plateau resulted in the formation of a large basin.
  • In due course of time, this depression gradually got filled with deposition of sediments by the rivers flowing from the mountains in the north and the peninsular plateau in the south. A flat land of extensive alluvial deposits led to the formation of the northern plains of India.

Himalayas

MAJOR PHYSIOGRAPHIC DIVISIONS

  1. The Himalayan Mountains: Trans Himalayas, Greater Himalayas, Shiwaliks, Purvanchal, Patkai Bum (North-East)
  2. The Northern Plains: Alluvial Plains majorly along Ganga River Basin, Alluvial Soil, Wheat, Rice etc.
  3. The Peninsular Plateau: Deccan Plateau, Black Soil (Regur), Cotton & other Cash Crops, Peninsular Rivers like the Narmada, Tapi, Godavari, Krishna, Mahanadi, Kaveri etc. Mountain ranges such as Western Ghats, Eastern Ghats, Nilgiri, Nallamala, Erramalla etc
  4. The Indian Desert: Thar Desert (Rajasthan)
  5. The Coastal Plains: The Arabian Sea, Bay of Bengal.
  6. The Islands: Lakshadweep, Andaman & Nicobar.

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