Structure and Physiography

India’s three geological divisions and six physiographic divisions: the mountains, the northern plain, the Peninsular plateau, the desert, the coastal plains and the islands.

Key ideas

• Geologically, India has the old, rigid Peninsular Block of gneisses and granites, the young, still-rising Himalayas, and the Indo-Ganga-Brahmaputra Plain filled with river sediments.
• The Himalayas act as a barrier and as a climatic, drainage and cultural divide.
• The northern plain runs from the hills down through the Bhabar, the Tarai and then the Bhangar and Khadar alluvium.
• The Deccan plateau is edged by the Western Ghats (higher, continuous) and the Eastern Ghats (low, broken by rivers), which meet at the Nilgiri hills.
• The Indian desert gets under 150 mm of rain, with dunes, barchans and salty playas; fossils show it was once under the sea.
• The western coastal plain is narrow and submerged with natural ports and no deltas; the eastern plain is broad and emergent with large deltas.
• The Andaman and Nicobar Islands (about 572) are raised submarine mountains with India’s only active volcano on Barren Island; Lakshadweep (about 36) is made of coral.

Remember

Watch out

• Swapping Bhangar (old) and Khadar (new) alluvium.
• Saying the west coast has big deltas: its rivers are short and swift.
• Calling Lakshadweep volcanic: it is coral; the volcano is on Barren Island.

Worked example