Structure: three blocks of different age
- Peninsular block: very old hard rocks (gneiss, granite). Stable, worn down into plateaus and old hills.
- Himalaya and other young mountains: formed when the Indian plate pushed into the Eurasian plate. Still rising; earthquakes happen.
- Indo-Ganga-Brahmaputra plain: a deep trough between the two, filled with river silt.
Northern and north-eastern mountains
Three parallel ranges
- Himadri (Great Himalaya): highest, average about 6,000 m, snow-covered. Mt Everest, Kanchenjunga.
- Himachal (Lesser Himalaya): 3,700–4,500 m. Pir Panjal, Dhaula Dhar. Hill stations like Shimla.
- Shiwalik (Outer Himalaya): 900–1,100 m, made of loose river gravel. Long flat valleys between Shiwalik and Himachal are duns (Dehradun).
Regional divisions (west to east)
Kashmir (north-western) Himalaya with Karakoram, Ladakh, Zaskar ranges; Himachal and Uttarakhand Himalaya; Darjiling and Sikkim Himalaya; Arunachal Himalaya.
North-eastern hills (Purvanchal)
The mountains bend south: Patkai Bum, Naga hills, Manipur hills, Mizo (Lushai) hills. Mostly sandstone, covered with forest.
Northern plain
Built by the Indus, Ganga and Brahmaputra and their tributaries. Very flat and very fertile. From the hills southward:
- Bhabar: 8–10 km belt of pebbles at the foot of the Shiwalik; small streams sink and vanish.
- Terai: the streams come up again; wet, marshy, once thick forest.
- Bhangar: older alluvium on higher land, above flood level; has lime nodules (kankar).
- Khadar: new alluvium on the flood plains, renewed each year; the most fertile.
Near the sea there are big deltas, like the Ganga–Brahmaputra delta (Sundarbans).
Peninsular plateau
A triangle of old hard rock, 600–900 m high, sloping gently to the east.
- Deccan plateau: much of it made of black lava rock (Deccan trap).
- Western Ghats (Sahyadri): high (900–1,600 m) and continuous. Anai Mudi (2,695 m) is the highest peak of the Peninsula.
- Eastern Ghats: low and broken into pieces by east-flowing rivers.
- North of the Deccan: Aravali (among the oldest fold mountains), Malwa plateau, Bundelkhand, Chhotanagpur plateau (rich in minerals).
- North-east: the Meghalaya plateau (Garo, Khasi, Jaintia hills), a piece of the Peninsula cut off by the Malda gap.
Indian desert
West of the Aravali hills, also called Marusthali.
- Less than 150 mm of rain a year; very hot days, cold nights.
- Crescent-shaped dunes called barchans, and long dunes.
- Rivers are short-lived; the Luni is the main one. Some streams end in salt lakes (e.g. Sambhar).
- Rocks show that this area was once under the sea.
Coastal plains
| Western coastal plain | Eastern coastal plain |
|---|---|
| Narrow, between the Western Ghats and the Arabian Sea | Wide, between the Eastern Ghats and the Bay of Bengal |
| A sunken (submerged) coast: good natural ports (Mumbai, Kochi) | A raised (emergent) coast: fewer natural ports |
| Rivers make estuaries, not deltas | Big deltas: Mahanadi, Godavari, Krishna, Kaveri |
| Parts: Kachchh–Kathiawar, Konkan, Goa (Kannad), Malabar (with lagoons, kayals) | Parts: Utkal, Andhra, Coromandel; lakes Chilika, Pulicat |
Islands
- Andaman and Nicobar (Bay of Bengal): about 570 islands; many are tops of an undersea mountain chain. Barren Island is India's only active volcano. The Ten Degree Channel separates Andaman from Nicobar.
- Lakshadweep (Arabian Sea): 36 small islands made of coral; low and flat. The Nine Degree Channel lies north of Minicoy.
Key formulas and definitions
- Himalaya N→S: Himadri (~6,000 m) → Himachal (3,700–4,500 m) → Shiwalik (900–1,100 m)
- Plain from hills: Bhabar → Terai → Bhangar (old) → Khadar (new)
- Western Ghats: high, continuous; Eastern Ghats: low, broken
- West coast: narrow, estuaries; East coast: wide, deltas
- Andaman & Nicobar: mountain tops + volcano; Lakshadweep: coral
Worked examples
1. Why is khadar more fertile than bhangar?
Khadar gets fresh silt every year in floods, so nutrients are renewed. Bhangar is older soil above flood level and has kankar.
2. Why do west-coast rivers make estuaries, not deltas?
They are short and fast, flowing down the steep Western Ghats, and the coast is sunken. They carry less silt and it is washed away.
3. Give two differences between the Western Ghats and the Eastern Ghats.
Western Ghats are higher and continuous; Eastern Ghats are lower and broken by rivers. Western Ghats are the source of big peninsular rivers.
4. Why is the Meghalaya plateau called a part of the Peninsular plateau?
It is made of the same old rocks; the Malda gap (a fault zone later filled with river silt) separated it from the Chhotanagpur plateau.
Common mistakes
- Putting the Shiwalik as the highest range. It is the lowest and outermost; Himadri is the highest.
- Mixing up bhabar and terai. Bhabar is pebbly and dry on top; terai is wet and marshy.
- Saying Lakshadweep islands are volcanic. They are coral; Barren Island (Andaman) is volcanic.
- Saying the east coast is narrow. The east coast is wide; the west coast is narrow.