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Class 11 Structure and Physiography: cheat sheet
CBSE Social Science. 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
| Highest Peninsular peaks | Anaimudi 2,695 m (Anaimalai hills); Dodabetta 2,637 m (Nilgiri hills) |
| Island peaks | Saddle Peak 738 m (North Andaman); Mount Thuiller 642 m (Great Nicobar) |
| Bhabar and Tarai | Bhabar 8–10 km of pebbles, streams vanish; Tarai 10–20 km, marshy, streams re-emerge |
| Bhangar and Khadar | Bhangar old alluvium; Khadar new alluvium |
| Northern plains | about 3,200 km long; area = length × width |
| Western Ghats local names | Sahyadri (Maharashtra), Nilgiri, Anaimalai and Cardamom hills |
| Channels | Ten Degree Channel splits the Andaman and Nicobar groups; Nine Degree Channel lies in Lakshadweep |
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
A Himalayan stream falls 1,443 m in 37 km; a Peninsular river falls 728 m in 182 km. Find each gradient in m per km. What landforms show the Himalayan rivers are in a youthful stage?
Working: 1,443 ÷ 37; 728 ÷ 182
Answer: Himalayan 39, Peninsular 4 m per km; gorges, V-shaped valleys, rapids and waterfalls
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