Physical geography of India

In short

Physical geography of India is the systematic study of the country's landforms, geological structure, drainage, climate, soils and natural vegetation, and of how these interact across a 3.287 million km² landmass between about 8°4′N and 37°6′N. It explains why the Punjab plains grow wheat, why Cherrapunji–Mawsynram is the wettest place on earth, why the Deccan trap soil suits cotton, and why the Himalayan belt is seismically the most dangerous part of the subcontinent. It is the structural half of every BA/MA Geography paper on India, and it is the bedrock of UPSC and State PSC general studies, SSC, NDA, forest-service and NET-JRF papers. Employers who use it directly include the Geological Survey of India, Survey of India, IMD, Central Ground Water Board, NRSC/ISRO, Forest Survey of India, state disaster-management authorities, and private GIS, infrastructure and agri-input firms. Interviews test whether a candidate can reason from a physical map rather than recite a list.

Explained

Structure, geology and physiographic divisions

• Three structural units: (1) the ancient, rigid Peninsular block of Archaean gneisses and schists; (2) the young, folded Himalayan mountains and the Indo-Burman arc; (3) the Indo-Gangetic–Brahmaputra plain, an alluvium-filled foredeep between them.
• Plate-tectonic cause: the Indian plate broke from Gondwana, drifted north and collided with the Eurasian plate from about 50-55 million years ago, closing the Tethys sea; the plate still moves north-northeast at roughly 5 cm/year, which keeps the Himalaya rising and seismically active.
• Geological time-table (broad): Archaean gneiss and Dharwar schists (oldest, mineral-rich) → Cuddapah and Vindhyan systems (unmetamorphosed sediments, diamond and building stone) → Gondwana system (Permo-Carboniferous, holds about 98% of India's coal) → Deccan trap basalt (Cretaceous-Eocene volcanism) → Tertiary Himalayan sediments → Quaternary alluvium.
• Standard physiographic divisions (six): the Northern/Trans-Himalaya; the Northern Plains; the Peninsular Plateau; the Indian Desert; the Coastal Plains; the Islands.
• Why the division matters: each unit has a distinct relief, rock type, soil, water regime and hazard profile, so land use, settlement and infrastructure design differ sharply across them.

The Himalaya and the north-eastern hills

• Longitudinal (parallel) ranges, north to south: Trans-Himalaya (Karakoram, Ladakh, Zanskar; K2 at 8,611 m lies in the Karakoram, in Pakistan-administered territory claimed by India); Greater Himalaya / Himadri (average 6,000 m, perpetually snow-covered, holds Kanchenjunga 8,586 m - India's highest peak, Nanda Devi 7,816 m); Lesser/Middle Himalaya (Himachal) - Pir Panjal, Dhauladhar, Mahabharat, 3,700-4,500 m, the hill stations and the Kashmir valley; Shiwaliks (outermost, 900-1,100 m, loose Tertiary gravels, highly erodible).
• Key boundary thrusts: Main Central Thrust, Main Boundary Thrust and Himalayan Frontal Thrust separate these belts; the Indus-Tsangpo suture marks the plate collision line.
• Duns/Doons: flat longitudinal valleys between the Lesser Himalaya and Shiwaliks (Dehra Dun, Kotli Dun, Patli Dun).
• Regional (transverse) divisions by river gaps: Punjab/Kashmir Himalaya (Indus-Satluj), Kumaon Himalaya (Satluj-Kali), Nepal Himalaya (Kali-Tista), Assam/Eastern Himalaya (Tista-Dihang).
• Purvanchal (north-eastern hills): Patkai Bum, Naga, Manipur, Mizo (Lushai) and Barail hills - the southward loop of the Himalayan arc after the Dihang (Namcha Barwa) syntaxial bend. The Garo-Khasi-Jaintia hills are *not* Purvanchal: the Meghalaya plateau is a detached north-eastward extension of the Peninsular block, separated from it by the Garo-Rajmahal gap; the Khasi hills carry the monsoon record rainfall.
• Glaciers and passes: Siachen (longest in India, Karakoram), Gangotri, Zemu; passes - Karakoram, Zoji La, Banihal, Rohtang, Shipki La, Nathu La, Bomdi La.

The Northern Plains and the Indian desert

• Formation: aggradational plain built by Indus, Ganga and Brahmaputra sediment in a foredeep; depth of alluvium commonly 1,000-2,000 m and locally much more; length about 2,400 km, width 150-300 km (wider in the west, narrow in Assam).
• Relief belts from the hills: Bhabar (coarse boulder-pebble piedmont where streams vanish underground) → Terai (marshy, re-emergent springs, dense forest, now largely reclaimed) → Bhangar (older alluvium, higher terraces, carries calcareous kankar nodules) → Khadar (new flood-plain alluvium, annually renewed, most fertile).
• Regional parts: Punjab-Haryana plain (doabs between the five rivers; Bist-Jalandhar, Bari, Rechna, Chaj doabs, with Sindh Sagar beyond the Jhelum); Ganga plain (upper, middle, lower - the lower grades into the Bengal/Sundarban delta); Brahmaputra (Assam) plain with the braided channel and Majuli, the large river island.
• Indian (Thar) desert: west of the Aravalli, below about 150 mm annual rainfall; barchan and longitudinal (seif) dunes, playas called rann, and ephemeral streams - the Luni is the only sizeable river. The Ghaggar is a seasonal stream often identified with the "lost" Saraswati.

The Peninsular Plateau, Ghats and coasts

• Nature: a triangular, tilted tableland of Archaean crystalline and Deccan basalt, 600-900 m average, tilting east, so most big rivers flow east; broken by block mountains and rift valleys (Narmada-Tapi grabens between the Satpura and Vindhya horsts).
• Sub-divisions: Central Highlands (Malwa, Bundelkhand, Chotanagpur with the mineral belt and the Rajmahal trap), Deccan Plateau (Maharashtra basalt plateau, Karnataka/Mysore plateau, Telangana and Andhra plateau), the Aravalli - the oldest fold mountain in India, highly denuded (Guru Shikhar, 1,722 m, in Mt Abu).
• Western Ghats (Sahyadri): continuous, steep western scarp, 900-1,600 m, rising southward; highest peak Anamudi (2,695 m) in the Anaimalai hills - the highest point in peninsular India; Doda Betta (2,637 m) in the Nilgiri; breached by the Palghat gap (about 24-30 km wide) and the Thal and Bhor Ghat passes. A UNESCO World Heritage site and one of the world's biodiversity hotspots.
• Eastern Ghats: discontinuous, lower (600 m average), dissected by the Mahanadi, Godavari, Krishna and Kaveri; the Nilgiri form the junction of the two Ghats.
• Coastal plains: the western coast is narrow, submergent, with lagoons/kayals (Kerala backwaters) and estuaries - divided into Kachchh-Kathiawar, Konkan, Kanara and Malabar; the eastern coast is wide, emergent, deltaic - Utkal, Andhra (Northern Circars) and Coromandel plains, with the Chilika lagoon (largest brackish lagoon in India) and Pulicat. Deltas: Mahanadi, Godavari, Krishna, Kaveri.
• Islands: Andaman and Nicobar - about 572 islands, tectonic/volcanic extension of the Arakan-Yoma arc; Barren Island is India's only active volcano; Saddle Peak (732 m) is the highest point; the 10° channel splits Andaman from Nicobar. Lakshadweep - about 36 coral islands (12 atolls, 3 reefs and submerged banks) on the Chagos-Laccadive ridge; the 9° channel separates Minicoy; Kavaratti is the capital.

Drainage system

• Classification by origin: Himalayan rivers - perennial (snowmelt + rain), antecedent/consequent in part, with large deltas and active meanders; Peninsular rivers - seasonal, broad shallow valleys near base level, mostly superimposed and non-meandering.
• Indus system: Indus with Jhelum, Chenab, Ravi, Beas and Satluj; the Indus Waters Treaty, 1960 (World Bank-brokered) gives India unrestricted use of the eastern rivers (Ravi, Beas, Satluj) and limited, non-consumptive use of the western three; India placed the treaty "in abeyance" in 2025 - the position has been evolving, so treat current status as subject to change.
• Ganga system: Bhagirathi + Alaknanda meet at Devprayag; left-bank tributaries Ramganga, Gomti, Ghaghara, Gandak, Kosi ("sorrow of Bihar", huge sediment and channel shifting); right-bank Yamuna (longest tributary), Son, Damodar ("sorrow of Bengal", now controlled by DVC). Ganga is India's longest river at about 2,525 km.
• Brahmaputra: rises as the Tsangpo in Tibet, enters India as the Dihang/Siang in Arunachal, becomes Brahmaputra in Assam, Jamuna in Bangladesh; enormous discharge and braiding, world's largest delta (Sundarban) with the Ganga.
• East-flowing peninsular rivers: Mahanadi, Godavari (largest peninsular river, "Dakshina Ganga"), Krishna, Kaveri, Pennar, Vaigai - all deltaic.
• West-flowing: Narmada and Tapi flow through rift valleys and form estuaries, not deltas, because the faulted trough carries sediment out to sea; also Sabarmati, Mahi, Luni, Periyar, Sharavati (Jog falls).
• Drainage patterns: dendritic (Ganga plain), radial (Amarkantak), trellis, rectangular (Vindhya), centripetal (Kashmir valley, Manipur). Watershed - the divide; the Western Ghats and the Aravalli-Delhi ridge are major divides.
• Lakes: tectonic (Wular - largest freshwater lake in India, in Jammu & Kashmir), oxbow (Kanwar), lagoon (Chilika, Vembanad, Pulicat), salt (Sambhar, Didwana), crater (Lonar), glacial (Pangong, Tso Moriri), man-made reservoirs (Govind Sagar, Nagarjuna Sagar).

Climate and the monsoon

• Type: tropical monsoon - "Amw/Aw/Cwg/BWh/BSh/Dfc/E" in Köppen's scheme as applied to India: Amw (monsoon with short dry season, Malabar coast), As (Coromandel), Aw (savanna, most of the peninsula), BShw (semi-arid steppe, Rajasthan-Punjab fringe), BWhw (hot desert, Thar), Cwg (Ganga plain, dry winter), Dfc (short-summer cold, Arunachal/Sikkim), E/ET (tundra/polar, high Himalaya).
• Controls: latitude and the Tropic of Cancer; the Himalaya as a climatic divide blocking cold Central Asian air; distance from the sea; relief and aspect (windward Ghats 250+ cm, leeward Pune 70 cm); the upper-air jet streams - subtropical westerly jet in winter, tropical easterly jet over peninsular India in summer; the Tibetan Plateau's heating; ENSO/El Niño (weak monsoon tendency), the Indian Ocean Dipole, and Eurasian snow cover.
• Four seasons (IMD): cold weather (December-February) - western disturbances bring winter rain to the north-west, vital for rabi wheat; hot weather (March-May) - loo, Kalbaisakhi/Norwester in Bengal, mango showers in Kerala-Karnataka; south-west monsoon (June-September) - onset over Kerala around 1 June (normal date; IMD revised the normal onset date series in 2020), two branches (Arabian Sea and Bay of Bengal) meeting over the north-west, breaks in the monsoon; retreating monsoon/post-monsoon (October-November) - October heat, north-east monsoon rain on Tamil Nadu, cyclones in the Bay.
• Mechanisms: differential land-sea heating and the ITCZ shift; the monsoon trough and its east-west oscillation; depressions tracking up the Ganga valley; El Niño-Southern Oscillation and the older Southern Oscillation (Walker) index used for forecasting.
• Distribution: average annual rainfall about 119 cm (IMD long-period average for the south-west monsoon season is about 87 cm, based on the 1971-2020 normals); Mawsynram/Cherrapunji above 1,000 cm; western Rajasthan and Ladakh below 10-20 cm. About 75-80% of annual rain falls in the four monsoon months, which makes the economy rainfall-dependent and the variability (coefficient of variation rising as mean rainfall falls) more important than the mean.
• Hazards: floods (Ganga-Brahmaputra plain), droughts (interior peninsula, Rajasthan), tropical cyclones (Bay of Bengal : Arabian Sea roughly 4:1), cold waves, heat waves, landslides (Shiwalik, Western Ghats), and earthquakes - the IS 1893 (Part 1): 2016 seismic zoning map has four zones, II to V, with Zone V (highest) covering the north-east, Kachchh, the Andaman-Nicobar, and parts of north Bihar and Uttarakhand.

Soils and natural vegetation

• ICAR/NBSS&LUP classification (eight major groups): Alluvial (about 40% of area, Northern Plains and deltas; khadar/bhangar; potash and lime rich, nitrogen and humus poor); Black/regur (Deccan trap, clayey, moisture-retentive, self-ploughing cracks, iron-rich, suits cotton); Red and yellow (crystalline peninsular rocks, iron oxide colour, low nitrogen and phosphorus); Laterite (heavy rain and alternate wet-dry leaching, acidic, poor in fertility but good for cashew, tea and bricks); Arid/desert (sandy, saline, low humus, kankar horizon); Saline and alkaline (reh/kallar/usar, from poor drainage and over-irrigation); Peaty and marshy (Kerala, Sundarban, high organic matter); Forest and mountain soils (thin, acidic in conifer belts).
• Soil erosion and conservation: sheet, rill, gully (Chambal ravines) and wind erosion; conservation by contour bunding and ploughing, terracing, strip cropping, shelter belts, check dams, afforestation; institutional work through the National Bureau of Soil Survey and Land Use Planning, Nagpur, and watershed programmes.
• Vegetation types (Champion and Seth classification): tropical evergreen and semi-evergreen (above 200 cm rain, Western Ghats, north-east, Andaman); tropical deciduous - moist (100-200 cm, teak, sal) and dry (70-100 cm); tropical thorn and scrub (below 70 cm, babool, khair, kikar); montane - wet temperate in the south and Himalayan temperate/alpine (deodar, pine, silver fir, birch, alpine meadows or bugyal); littoral and swamp (mangrove) - the Sundari of the Sundarban.
• Conservation framework: the Indian Forest Act, 1927; the Wild Life (Protection) Act, 1972; the Forest (Conservation) Act, 1980 (amended 2023 and renamed Van (Sanrakshan Evam Samvardhan) Adhiniyam); the Biological Diversity Act, 2002 (amended 2023); the Environment (Protection) Act, 1986; CAMPA for compensatory afforestation. The Forest Survey of India's India State of Forest Report gives forest cover around 21-22% of the geographical area against the National Forest Policy, 1988 target of 33%; the ISFR is biennial, so quote the latest edition's figure.
• Biogeographic richness: four global biodiversity hotspots touch India - the Himalaya, Indo-Burma, Western Ghats-Sri Lanka and Sundaland (Nicobar); biosphere reserves, national parks, wildlife sanctuaries and Ramsar wetlands form the protected network.

Key points

• Three structural units - Peninsular block (old and stable), Himalaya (young fold), Northern Plain (alluvial foredeep).
• Collision tectonics - Indian plate collided with Eurasia about 50-55 Ma; northward motion about 5 cm/year keeps the Himalaya rising.
• Himalayan ranges - Trans-Himalaya, Himadri, Himachal, Shiwalik; Kanchenjunga (8,586 m) is the highest peak within India.
• Duns - longitudinal valleys between Lesser Himalaya and Shiwalik; Dehra Dun is the classic example.
• Plain sequence - Bhabar, Terai, Bhangar, Khadar from the foothills to the flood plain; khadar is the most fertile.
• Doab - the land between two confluent rivers; Punjab's five rivers create the Bist-Jalandhar, Bari, Rechna and Chaj doabs.
• Deccan trap - Cretaceous-Eocene basalt lava flows; parent rock of black cotton (regur) soil.
• Rift valleys - the Narmada and Tapi flow in faulted troughs and make estuaries, not deltas.
• Western vs Eastern Ghats - continuous, higher, steep-scarped vs discontinuous, lower, river-dissected; they meet at the Nilgiri.
• Anamudi (2,695 m) - highest peak of peninsular India; Palghat gap is the major Western Ghats breach.
• Coast contrast - west coast narrow and submergent with backwaters; east coast broad, emergent and deltaic.
• Islands - Andaman-Nicobar are tectonic/volcanic (Barren Island active); Lakshadweep are coral atolls.
• Godavari - largest peninsular river by basin and length; Ganga (about 2,525 km) is India's longest.
• Monsoon - seasonal reversal of winds driven by differential heating, ITCZ shift, jet streams and Tibetan heating; 75-80% of rain in June-September.
• Western disturbances - extratropical lows from the Mediterranean that give north-west India its winter rain for rabi crops.
• Köppen in India - Amw, As, Aw, BShw, BWhw, Cwg, Dfc and E types occur, showing the climatic diversity.
• Soils - alluvial (largest extent), black, red-yellow, laterite, arid, saline-alkaline, peaty, forest; classified by NBSS&LUP/ICAR.
• Seismic zoning - IS 1893 (Part 1): 2016 defines Zones II-V; Zone V includes the north-east, Kachchh and the Andaman-Nicobar.

Formulas and examples

• Rainfall departure (monsoon performance): a district has a normal south-west monsoon rainfall of 850 mm and records 620 mm.
  • Departure = (620 − 850)/850 × 100 = −230/850 × 100 = −27.1% → falls in the Deficient class (−20% to −59%), so a rabi irrigation advisory is justified.
• Rainfall reliability, Jaisalmer vs Thiruvananthapuram: suppose annual rainfall means of 180 mm (σ = 90 mm) and 1,800 mm (σ = 270 mm).
  • Jaisalmer CV = 90/180 × 100 = 50%; Thiruvananthapuram CV = 270/1,800 × 100 = 15%.
  • Inference: the arid station's rainfall is three-plus times less reliable - which is exactly the general rule that variability increases as mean rainfall decreases, and why Rajasthan farming is risk-prone.
• Lapse rate and a hill station: Kozhikode (sea level) records 30 °C. Estimate the temperature at Ooty, about 2,200 m.
  • Fall = 6.5 × (2,200/1,000) = 6.5 × 2.2 = 14.3 °C → expected temperature = 30 − 14.3 = 15.7 °C.
  • This orographic cooling is why hill stations sit on the Nilgiri and the Lesser Himalaya.
• Drainage density: a Chotanagpur sub-basin of 450 km² has total mapped stream length 1,080 km.
  • Dd = 1,080/450 = 2.4 km/km² - a moderately high density, typical of impermeable crystalline rock with sparse vegetation and intense monsoon runoff; a permeable Bhabar tract would give a far lower value.
• Basin water balance: a basin of area 20,000 km² receives 1,000 mm of rain in a season; measured runoff at the gauge is 6.0 km³ and change in storage is negligible.
  • Rainfall volume = 1,000 mm = 1.0 m over 20,000 km² = 20,000 × 10⁶ m² × 1.0 m = 20 × 10⁹ m³ = 20 km³.
  • Runoff coefficient = 6.0/20 = 0.30; evapotranspiration = 20 − 6.0 − 0 = 14 km³ (70% of rainfall), a plausible share for a monsoon-fed peninsular basin.

Where it is used

• Geological and mineral survey: the Geological Survey of India maps stratigraphy and structure; the Gondwana, Dharwar and Cuddapah systems guide coal, iron-ore and diamond exploration and the National Geoscience Data Repository.
• Survey, mapping and remote sensing: Survey of India toposheets and the open-series maps, NRSC/ISRO Bhuvan land-use and flood-mapping, state GIS cells - roles as cartographer, GIS analyst, image interpreter.
• Water resources and irrigation: Central Ground Water Board aquifer mapping by geology (hard-rock Deccan vs alluvial Ganga), Central Water Commission flood forecasting, river-basin and interlinking studies, dam siting on the Narmada and Mahanadi.
• Meteorology and agriculture: IMD forecasting, agro-climatic zoning used by ICAR and state agriculture departments, crop insurance under PMFBY based on rainfall and soil zones, agri-input and seed companies choosing products by soil group.
• Disaster management and infrastructure: NDMA and state authorities use seismic zones (IS 1893 Part 1: 2016), flood plain zoning, landslide susceptibility and the Coastal Regulation Zone Notification for coastal projects; highway, railway and tunnel alignment in the Shiwalik and Western Ghats.
• Environment, forestry and tourism: Forest Survey of India's ISFR, environmental impact assessment, eco-sensitive zone notification in the Western Ghats, Ramsar wetland management, and physical-geography-based tourism, teaching and competitive-exam coaching.

Interview questions

• Q: Why do most large Indian peninsular rivers flow east? A: The Peninsular block is tilted eastward, so the Western Ghats act as the water divide close to the west coast and the general slope carries the Mahanadi, Godavari, Krishna and Kaveri to the Bay of Bengal.
• Q: Why do the Narmada and Tapi form estuaries instead of deltas? A: They flow in faulted rift valleys with steep gradients and hard rock, carry little silt and discharge into a trough, so tidal action removes sediment instead of letting it build a delta.
• Q: What is the difference between khadar and bhangar? A: Khadar is new flood-plain alluvium, renewed annually and more fertile; bhangar is older, higher terrace alluvium containing calcareous kankar nodules and is less productive.
• Q: Why does Shillong receive heavy rain while Guwahati, close by, is much drier? A: The Khasi hills face the Bay of Bengal branch head-on and force the moist air to rise (orographic lift), whereas Guwahati lies in the Brahmaputra valley in a relative rain-shadow.
• Q: What are western disturbances and why do they matter economically? A: Extratropical cyclones moving in from the Mediterranean-Caspian region with the subtropical westerly jet; their winter rain and snow over north-west India is critical for rabi wheat and for Himalayan snowpack.
• Q: Explain the Bhabar-Terai sequence. A: Rivers leaving the hills dump coarse boulders in the porous Bhabar belt and go underground; they re-emerge as springs in the finer, marshy Terai belt downslope.
• Q: Why is the north-east in the highest seismic zone? A: It sits at the syntaxial bend where the Indian plate underthrusts both the Himalayan arc and the Indo-Burman arc, with active thrusts and high strain accumulation, so IS 1893 places it in Zone V.
• Q: Which is longer, the Ganga or the Godavari, and which drains more of peninsular India? A: The Ganga is far longer (about 2,525 km) and is India's longest river; the Godavari (about 1,465 km) is the longest and largest river entirely within peninsular India.
• Q: Why is black soil suited to cotton without heavy irrigation? A: Its high clay (montmorillonite) content retains moisture, and it is rich in iron, lime, magnesia and potash; deep cracks on drying aerate and self-plough it, though it is poor in nitrogen and phosphorus.
• Q: Why is laterite soil infertile despite forming in high-rainfall areas? A: Heavy rain with alternating wet and dry spells leaches away silica and bases, leaving acidic iron and aluminium oxides low in nitrogen, phosphate, lime and organic matter.
• Q: What is the role of the tropical easterly jet in the Indian monsoon? A: It forms over peninsular India in summer above the heated Tibetan Plateau and helps maintain the low-level inflow and the strength of the south-west monsoon; its weakening is linked to monsoon breaks.
• Q: Are the Andaman and Lakshadweep islands of the same origin? A: No - the Andaman and Nicobar group is a tectonic-volcanic extension of the Arakan-Yoma fold arc, while Lakshadweep is a set of coral atolls built on a submarine ridge.
• Q: How do you explain Tamil Nadu's winter rain when the rest of India is dry? A: The retreating north-east monsoon winds pick up moisture over the Bay of Bengal and strike the Coromandel coast, which also receives October-December cyclonic rain.

Common mistakes

• Treating the Himalaya as one range instead of distinct parallel belts, and calling Mount Everest or K2 an Indian peak - the highest peak within India is Kanchenjunga.
• Reversing khadar and bhangar, or confusing Bhabar with Terai in the piedmont sequence.
• Saying all peninsular rivers lack deltas - the east-flowing rivers have large deltas; only the rift-valley Narmada and Tapi have estuaries.
• Describing the monsoon as a simple sea-breeze; examiners expect the ITCZ shift, jet streams, Tibetan heating and ENSO/IOD controls.
• Confusing the Eastern Ghats with the Eastern Coastal Plain, and calling the Aravalli a block mountain - it is the oldest, heavily denuded fold mountain.
• Quoting soil groups by old or foreign classifications instead of the current ICAR/NBSS&LUP eight-group scheme, or claiming black soil is volcanic "lava soil" rich in nitrogen.
• Quoting stale figures - forest cover, monsoon normals and seismic codes are revised, so cite the latest ISFR, the IMD 1971-2020 normals and IS 1893 (Part 1): 2016 rather than remembered numbers.
• Mixing units in calculations - mm of rainfall with km³ of volume, or metres with kilometres in gradient and drainage-density problems.

Related topics

Resources and economy of India · Geomorphology: landforms and processes · Climatology and oceanography · Soil geography and biogeography · Disaster management and hazard mapping · Cartography, remote sensing and GIS