Structure and Physiography

India's varied physiography — soaring Himalayas, vast alluvial plains, ancient plateaus, and dynamic coasts — results directly from its geological history. Understanding why the Himalayas are young and still rising, why the Deccan Plateau is ancient and stable, and why the Indo-Gangetic Plain is so fertile requires tracing India's journey from Gondwanaland to its current position. This chapter is one of the most map-intensive for UPSC — physiographic divisions, mountain ranges, and river basins are consistently tested.

PART 1 — Quick Reference Tables

Table 1: India's Geological History

Table 2: The Himalayan Mountain System

Table 3: Major Himalayan Peaks in India

Table 4: Physiographic Divisions of India

Table 5: Eastern vs Western Coastal Plains

PART 2 — Detailed Notes

India's Geological Heritage: The Indian Plate

The Indian Plate — the tectonic foundation of the Indian subcontinent — is one of the oldest continental fragments on Earth. The Peninsular Plateau, sometimes called the Indian Shield or Deccan Plateau, is composed of ancient Archaean (Precambrian) rocks (~3,000+ million years old) — among the world's oldest exposed rock formations.

When Gondwanaland existed (~300–200 mya), India was adjacent to Africa, Australia, and Antarctica. The similar geological formations and fossil evidence across these continents (Glossopteris flora, Mesosaurus reptile) confirmed Wegener's continental drift theory. India broke away from Gondwanaland ~150–200 mya and drifted northward across the Tethys Sea.

The Tethys Sea: A warm, shallow sea that existed between the Indian/Gondwana landmass and Eurasia. When India collided with Eurasia, the Tethys Sea was obliterated — its marine sedimentary rocks were buckled upward to form the Himalayas. This is why marine fossils (ammonites, echinoids) are found in Himalayan limestone rocks at elevations >4,000 m.

The Himalayas: Young, Rising, and Seismically Active

The Himalayas are young fold mountains formed in the Cenozoic era (~50 million years ago to present) as the Indo-Australian Plate continues to push northward. India moves ~5 cm northward every year — the Himalayas are still rising at ~5 mm/year (geological uplift exceeds erosion in much of the range).

Three parallel ranges:

Himadri (Great/Inner Himalayas): The northernmost and highest range. Permanently snow-covered peaks: Mt. Everest (8,849 m — highest point on Earth), Kangchenjunga (8,586 m — India's highest), Makalu, Lhotse. Houses the major glaciers: Gangotri, Zemu, Siachen. The Siachen Glacier (~72 km long) is the world's longest glacier outside the polar regions.

Himachal (Lesser/Middle Himalayas): 60–80 km wide, 3,700–4,500 m elevation. Contains the major hill stations: Shimla, Mussoorie, Nainital, Darjeeling. The Pir Panjal and Dhaula Dhar ranges belong here. The Kashmir Valley lies between Himadri and Pir Panjal — a famous synclinal depression.

Siwaliks (Outer Himalayas): Youngest and lowest (600–1,500 m). Composed of relatively unconsolidated sediments eroded from the main Himalayas. Contains dun valleys — longitudinal valleys between Siwaliks and Lesser Himalayas (Dehra Dun, Patli Dun, Kotli Dun). South of Siwaliks is the terai — a marshy, forested belt of alluvial soils.

Longitudinal divisions: The Himalayas are also divided from west to east:

• Punjab/Kashmir Himalayas (Jhelum to Sutlej)
• Kumaon/Garhwal Himalayas (Sutlej to Kali)
• Nepal Himalayas (Kali to Tista) — includes Everest
• Assam/Arunachal Himalayas (Tista to Brahmaputra — Namcha Barwa)
• Eastern Hills (Purvanchal): Patkai, Naga, Manipur, Mizo hills — south of Brahmaputra; trending north–south; form India's border with Myanmar

💡 Explainer: The Indo-Gangetic Plain

As the Himalayas rose, their weight depressed the crust to the south, creating a foredeep (a trough in front of the mountain range). This trough was gradually filled by sediments eroded from the rising Himalayas, creating the Indo-Gangetic Plain — the world's most extensive alluvial plain.

The plain stretches ~3,200 km from Punjab (Pakistan) to the Brahmaputra valley in Assam, and is 150–300 km wide. The depth of alluvium reaches up to 3,000 m in some places — meaning that the original rocky basement is buried 3 km below the surface.

The plain is divided into three sub-plains:

• Bhangar (old alluvium): Higher, older alluvial terraces; less fertile; does not flood
• Khadar (new alluvium): Lower, younger; renewed by annual flooding; more fertile; used for intensive agriculture
• Terai: Marshy, forested southern margin of alluvial plain; now largely cleared for agriculture

Why is the Northern Plain so fertile?

• Deep, well-drained alluvial soil
• Flat terrain — easy to irrigate and plough
• Numerous perennial rivers (Himalayan — fed by glaciers and monsoon)
• Annual flood renewal of nutrient-rich sediment in khadar areas

The Peninsular Plateau: Ancient Stability

The Peninsular Plateau is a tableland composed of old crystalline, igneous, and metamorphic rocks — the oldest landmass in India. It covers ~16 lakh km² — the largest physiographic unit.

Structure: Two major divisions:

• Central Highlands: North of Narmada river — Malwa Plateau, Vindhyan ranges, Bundelkhand, Baghelkhand; slopes northward; drained by Chambal, Betwa, Ken (Ganga system tributaries)
• Deccan Plateau: South of Narmada — triangular; slopes eastward toward Bay of Bengal; drained by Mahanadi, Godavari, Krishna, Cauvery (eastward flowing); bounded by Western and Eastern Ghats

Western Ghats: Continuous escarpment running parallel to west coast; 1,600 km long; 900–2,695 m (Anamudi = 2,695 m, highest peak in peninsular India, in Kerala). The western face is steep (abrupt scarp); eastern face is gentle slope to Deccan. Contains three main passes: Thal Ghat, Bhor Ghat, Pal Ghat (Palakkad Gap — only major break; allows Arabian Sea branch of monsoon to enter Tamil Nadu).

Eastern Ghats: Discontinuous, lower (600–900 m), cut by major rivers (Mahanadi, Godavari, Krishna, Cauvery). Not as continuous a barrier as Western Ghats.

🎯 UPSC Connect: Deccan Traps and Black Cotton Soil

The Deccan Traps were formed when massive volcanic eruptions ~66 million years ago poured basaltic lava over ~500,000 km². The thick lava flows cover much of Maharashtra, Madhya Pradesh, Karnataka, and Gujarat.

Weathering of basalt produces regur (black cotton soil) — one of the world's most fertile soils:

• Rich in iron, calcium, aluminium hydroxides
• Clay-dominant — expands when wet, contracts when dry (self-ploughing)
• Retains moisture well
• Suitable for dryland cotton cultivation without irrigation
• Also supports sorghum (jowar), groundnut, wheat

This is why Maharashtra is a major cotton-growing state and why Vidarbha (eastern Maharashtra, semi-arid regur soil zone) is associated with farmer distress during drought years — the soil and crops are moisture-dependent.

PART 3 — Frameworks & Analysis

Physiographic Divisions: Key Comparisons

Mountain Ranges of India: East to West

Exam Strategy

Prelims Traps:

• Anamudi (2,695 m) is the highest peak in peninsular India (not India — Kangchenjunga/8,586 m is India's highest).
• Nanda Devi (7,816 m) is the highest peak entirely within India (Kangchenjunga is on the India–Nepal border).
• Deccan Traps are basaltic (volcanic extrusive) — formed from lava, not from sediment.
• Bhangar = old alluvium (higher, less fertile). Khadar = new alluvium (lower, more fertile, flood-prone).
• Palakkad (Palghat) Gap is the only major break in the Western Ghats — allows NE monsoon to bring rain to Tamil Nadu.
• Western Ghats are on the western edge of the Deccan Plateau, NOT the western coast directly (there is coastal plain between the Ghats and the sea).

Mains Frameworks:

• "Explain the physiographic diversity of India and its economic implications" — use 5 divisions + their economic significance.
• Himalayan rivers vs Peninsular rivers — differences in regime, sediment load, navigability, flood potential.
• Geological history → mineral distribution: Peninsular shield → iron, manganese; Gondwana sedimentary basins → coal; Deccan Traps → black soil, basalt.

Previous Year Questions

1. UPSC Prelims 2021: Which of the following is the highest peak in peninsular India? (Anamudi — 2,695 m)
2. UPSC Prelims 2018: What is 'Dun'? (Longitudinal valley between Shivaliks and Lesser Himalayas)
3. UPSC Mains GS1 2014: Explain the factors responsible for the formation of the northern plains of India and discuss their significance.
4. UPSC Mains GS1 2020: Describe the geological and geomorphological features of the Indian subcontinent that have contributed to its economic development.