Chapter: Structure and Physiography

• Introduction

  • Age of Earth: Approx 460 million years (Correction: 460 crore / 4.6 billion years)
  • Geological processes shaped relief features
  • Diversity in relief: High mountains, deep valleys, extensive plains

• Earth’s Geological Structure

  • Peninsular Block
    • Formed of ancient gneisses and granites
    • Rigid shield, stable landmass
    • Extension up to Rajmahal hills and Meghalaya plateau
  • Himalayas and Other Peninsular Mountains
    • Young, weak, and flexible fold mountains
    • Formed due to tectonic folding of sedimentary rocks
    • High relief, fast-flowing rivers, deep gorges
  • Indo-Ganga-Brahmaputra Plain
    • Geosynclinal depression (Tethys sea fill)
    • Formed by alluvial deposits from Himalayas and Peninsula

• Physiographic Divisions of India

  • 1. The Northern and North-Eastern Mountains (Himalayas)
    • Greater Himalayas (Inner/Himadri): Core of granite, continuous range, highest peaks (Mt. Everest, Kanchenjunga)
    • Lesser Himalayas (Himachal): Rugged ranges, famous valleys (Kashmir, Kangra, Kullu), hill stations
    • Outer Himalayas (Shivaliks): Outermost range, composed of unconsolidated sediments, Dun formations (Dehra Dun)
    • Regional Divisions: Kashmir Himalayas, Himachal/Uttaranchal Himalayas, Darjeeling/Sikkim Himalayas, Arunachal Himalayas, Eastern Hills/Purvanchal
  • 2. The Northern Plains
    • Formed by Indus, Ganga, and Brahmaputra river systems
    • Dimensions: ~3,200 km east to west, width 150-300 km
    • Relief/Morphological Features:
      • Bhabar: Porous pebble belt along Shivalik foothills (streams disappear)
      • Terai: Wet, marshy, thickly forested zone south of Bhabar
      • Bangar: Older alluvial plain, contains kankar (calcareous deposits)
      • Khadar: Newer alluvial floodplains, very fertile
  • 3. The Peninsular Plateau
    • Broad and shallow depression, tableland
    • Major Sub-divisions:
      • Central Highlands: Bound by Aravalis and Vindhyas, Malwa plateau, Chotanagpur plateau
      • Deccan Plateau: Triangular landmass, bounded by Western Ghats, Eastern Ghats, and Satpura
      • North-Eastern Plateau: Meghalaya plateau (Shillong plateau) and Karbi Anglong plateau
  • 4. The Indian Desert
    • Northwest of Aravali hills (Thar Desert)
    • Arid topography, low rainfall (<150 mm/year)
    • Features: Barchans (crescent-shaped dunes), mushroom rocks, shifting dunes, inland drainage (Luni river)
  • 5. The Coastal Plains
    • Western Coastal Plain: Narrow belt, submerged plain, divided into Konkan, Kannad, and Malabar coasts (backwaters/kayals)
    • Eastern Coastal Plain: Wider, emergent plain, deltas of Mahanadi, Godavari, Krishna, and Kaveri (Northern Circars, Coromandel coast)
  • 6. The Islands
    • Andaman and Bay of Bengal Islands: Elevated submarine ridges, volcanic origin (Barren Island), coral deposits
    • Lakshadweep and Arabian Sea Islands: Group of coral islands (Atolls), Minicoy is the largest