Physiographic Sub-Units of India
Master the detailed classification of India's physiographic divisions — Northern Mountains, Great Plains, Peninsular Plateau, Coasts, Deserts, and Islands for UPSC Prelims & Mains.
1. The Northern Mountains (Himalayas & Purvanchal)
The Northern Mountains are divided into the Trans-Himalayas, the Himalayan mountain range, and the Purvanchal (Eastern Hills).
- Trans-Himalayas: Karakoram, Ladakh, and Zaskar ranges. Mostly dry, cold desert conditions.
- Greater Himalayas (Himadri): Highest peaks (Everest, Kanchenjunga). Continuous, composed of granite core.
- Lesser Himalayas (Himachal): Pir Panjal, Dhauladhar, Mahabharat ranges. Highly rugged, famous hill stations.
- Outer Himalayas (Shiwaliks): Youngest range, made of consolidated sediments, characterized by flat valleys called **Duns** (e.g., Dehradun).
- Kashmir/Western Himalayas: Famous for Karewa formations (saffron), cold deserts.
- Kumaon Himalayas: Between Satluj and Kali rivers; contains peaks like Nanda Devi.
- Sikkim-Darjeeling Himalayas: Fast-flowing rivers, orchid flora, tea plantations.
- Arunachal/Eastern Himalayas: High rainfall, deep gorges, home to tribes.
- Purvanchal: Patkai Bum, Naga Hills, Manipur Hills, and Mizo Hills.
Himalayan Cross-Section Profile:
Schematic Section of Himalayan Zones
2. The Northern Plains & The Peninsular Plateau
The Plains and the Plateau form the agricultural and mineral backbone of India, respectively.
- Bhabar: Porous gravel zone at foothills. Rivers run underground.
- Terai: Swampy zone where rivers re-emerge; rich in biodiversity.
- Bhangar: Older clayey alluvium forming upland terraces. Contains calcium nodules called **kankar**.
- Khadar: Young, fertile alluvial silt renewed annually by floods.
- Central Highlands: Malwa Plateau, Bundelkhand, Baghelkhand. Bordered by Aravalli and Vindhyan ranges.
- Deccan Plateau: Maharashtra, Karnataka, and Telangana plateaus. Stepped basalt topography.
- Northeastern Extension: Meghalaya (Garo, Khasi, Jaintia hills) and Mikir hills. Structurally part of Peninsular block.
- Chotanagpur Plateau: Rich in minerals (coal, iron). Damodar valley coal graben.
3. Coastal Plains, Western & Eastern Ghats, and Islands
The coastal tracts, mountain borders, and oceanic islands form distinct ecological and structural zones.
- Western Ghats (Sahyadris): High, continuous, steep western slope. Thal Ghat, Bhor Ghat, and Pal Ghat are key passes. Highest peak: **Anamudi**.
- Eastern Ghats: Discontinuous, highly dissected by east-flowing rivers. Average elevation is lower. Highest peak: **Jindhagada / Mahendragiri**.
- Western Coastal Plains: Narrow, submergent coast. Divided into Konkan, Kannad, and Malabar coasts. Features lagoons (Kayals).
- Eastern Coastal Plains: Broad, emergent coast. Divided into Northern Circars and Coromandel coast. Famous for large river deltas.
- Islands: Andaman & Nicobar (tectonic upliftment, volcanic activity like Barren Island) and Lakshadweep (atoll coral islands in the Arabian Sea).
Physiographic Evolution Milestones
- Shield Formation (>540 Ma) — Precambrian Crystalline Shields: Consolidation of the ancient Aravalli, Singhbhum, and Dharwar cratons, forming the bedrock shield of the Peninsular Plateau.
- Carboniferous-Permian (300-200 Ma) — Gondwana Sedimentation: Tectonic downfaulting in the Peninsula created grabens (Damodar, Mahanadi, Godavari) accumulating rich plant matter which formed Gondwana coal.
- Late Cretaceous (66 Ma) — Deccan Volcanism: Massive flood basalt eruptions covered the north-western Peninsula, creating the flat-topped stepped Deccan Trap landscape.
- Tertiary Period (50-2 Ma) — Himalayan Orogeny: Three distinct folding phases uplifted the Trans-Himalayas, Greater Himalayas, Lesser Himalayas, and finally the Shiwaliks.
- Pleistocene-Holocene (2 Ma - Present) — Indo-Gangetic Basin Infill: Accumulation of massive sediment volumes in the foredeep basin between the rising Himalayas and the stable shield, forming the fertile Northern Plains.
Memory Aids
- Mnemonic 1: North-South Order of Karakoram, Ladakh, Zaskar, Kailash, Pir Panjal: North to South sequence of ranges: **K**arakoram $\rightarrow$ **L**adakh $\rightarrow$ **Z**askar $\rightarrow$ **P**ir Panjal.
- Mnemonic 2: Passes on the Western Ghats (North to South): North to South order of major Western Ghats passes: **T**hal Ghat (Mumbai-Nashik) $\rightarrow$ **B**hor Ghat (Mumbai-Pune) $\rightarrow$ **P**al Ghat (Kochi-Chennai).
Common Exam Traps
- Trap 1: Meghalaya Plateau Connection: The Meghalaya (Shillong) Plateau and Karbi Anglong are NOT part of the Himalayas. They are geologically extensions of the **Peninsular Plateau**, separated from it by the Malda Fault (Garo-Rajmahal Gap).
- Trap 2: Western vs Eastern Ghats Continuity: A common trap is assuming both Ghats are continuous. The **Western Ghats are continuous** and can be crossed only through passes, while the **Eastern Ghats are highly dissected, discontinuous**, and broken by major east-flowing rivers (Mahanadi, Godavari, Krishna, Kaveri).
- Trap 3: Bhabar vs Terai Characteristics: Bhabar is a dry, porous belt of gravels where streams disappear. Terai is a wet, swampy, marshy forest belt just south of Bhabar where streams re-emerge. Confusing these two is a classic UPSC trap.
- Trap 4: Island Origins: Lakshadweep islands are of **coral origin** (built up by polyps), whereas the Andaman and Nicobar islands are of **tectonic/volcanic origin** (submarine tertiary mountain ranges rising from the ocean floor).