Introduction
India's physiography exhibits remarkable geo-diversity shaped by endogenic tectonic movements and persistent exogenic processes. Based on relief, structure, and geological history, the Geological Survey of India and NCERT classify the country into six distinct physiographic divisions.
1. The Northern and North-Eastern Mountains
The Himalayas represent tectonically active, young fold mountains formed by the collision of the Indian and Eurasian plates. They comprise three parallel ranges: the Himadri (Greater Himalayas), the Himachal (Lesser Himalayas), and the Shiwaliks (outer foothills), extending eastwards into the Purvanchal hills. These ranges serve as an indispensable climatic barrier against cold Central Asian winds and function as a perennial freshwater reservoir for major river systems.
2. The Northern Plains
Formed in an aggradational foreland basin by alluvial deposition from the Indus, Ganga, and Brahmaputra river systems, this 2,400 km long fertile plain serves as India's agricultural heartland. Geomorphologically, it is stratified from north to south into distinct belts:
- Bhabar: A narrow, highly porous pebble-gravel zone along the Shiwalik piedmont where streams disappear underground.
- Terai: A swampy, marshy lowland zone where submerged streams re-emerge, sustaining dense vegetation and biodiversity.
- Bhangar: Older alluvium situated above current flood levels, characterized by calcareous nodules known as kankar.
- Khadar: Younger, highly fertile alluvium deposited annually on dynamic floodplains.
3. The Peninsular Plateau
The oldest and most stable geological block of India, the Peninsular Plateau is a rigid shield composed primarily of Archaean granites and gneisses, interspersed with volcanic basalt in the Deccan Trap. Flanked by the steep, continuous Western Ghats (Sahyadris) and the low, dissected Eastern Ghats, this mineral-rich tableland houses the majority of India's metallic, non-metallic, and fossil fuel reserves.
4. The Indian Desert (Thar)
Situated to the northwest of the relict Aravalli Range, the Thar Desert is an undulating tract dominated by arid geomorphic landforms such as barchans, longitudinal sand dunes, and pediments. It receives less than 150 mm of annual rainfall and features an inland drainage network anchored by ephemeral streams such as the Luni River.
5. The Coastal Plains
Flanking the Peninsular Plateau along the Arabian Sea and Bay of Bengal, the coastal plains exhibit marked contrasting characteristics:
- Western Coastal Plain: A narrow, submergent coast marked by estuaries, steep rocky cliffs, and backwater lagoons (locally known as kayals, prominent along the Malabar Coast).
- Eastern Coastal Plain: A broad, emergent coastal strip marked by extensive fertile deltas formed by east-flowing rivers such as the Mahanadi, Godavari, Krishna, and Kaveri.
6. The Islands
India includes two major offshore island archipelagos with contrasting genesis:
- Andaman and Nicobar Islands: Located in the Bay of Bengal, these represent the subaerial peaks of submerged Tertiary fold mountain chains (Arakan Yoma extension) and include India's only active volcano, Barren Island.
- Lakshadweep Islands: Situated in the Arabian Sea, this group consists of 36 low-lying coral atolls and fringing reefs of biogenic origin.
Conclusion
These physiographic macro-units form a mutually supportive and interdependent geographical system: the northern mountains secure water and climate stability, the alluvial plains sustain food security, the plateau fuels industrial development, and the long coastline and island territories anchor blue economic and maritime growth.