Physiographic Divisions of India

Most aspirants can name India's mountains, plains and plateaus but cannot say why each one looks the way it does. UPSC rarely asks "what is the Northern Plain"; it asks which range a peak sits on, how many states a mountain chain runs through, or which of two lookalike rivers actually rises in the range named. Those questions only fall if the underlying physical facts, rock type, age, and the process that built each landform, are on recall, not just the name.

Himalayan and Peninsular Drainage Systems covers this same landmass from the rivers' point of view: which system is perennial, which is antecedent, how the Indo-Brahma river is believed to have evolved. This note stays on the land itself, the mountain ranges, plains, plateaus, coasts and islands as physical units, what each is made of, how old it is, and how it formed, which is a genuinely different set of facts from anything about drainage.

Three Geological Regions, Six Physiographic Divisions

India's landmass separates into three geological regions that behave completely differently under stress. The Peninsular Block is a complex of very ancient gneisses and granites that has stood as a rigid, stable landmass since the Cambrian period, over 500 million years, disturbed only by vertical block faulting (the rift valleys of the Narmada, the Tapi and the Mahanadi, and the Satpura block mountains) and by the submergence of part of its western edge. The Himalaya and the other Peninsular mountains, by contrast, are young, weak and flexible, still being actively folded, faulted and thrust upward, which is why their rivers run through gorges and V-shaped valleys in a youthful, erosional stage. Between the two sits the Indo-Ganga-Brahmaputra Plain, originally a geo-synclinal depression that reached its deepest development around 64 million years ago, during the third phase of Himalayan mountain building, and has since been filled by sediment to an average alluvial depth of 1,000 to 2,000 metres.

On the ground, these three geological regions express themselves as six physiographic divisions: the Northern and North-eastern Mountains, the Northern Plain, the Peninsular Plateau, the Indian Desert, the Coastal Plains, and the Islands. The rest of this note works through each in turn, ending on the two places UPSC actually tests this chapter, matching a place to its physiographic or cultural region, and counting the states a range or lake spans.

The Himalayan System: Four Parallel Ranges

The Himalaya is not one ridge but four parallel ranges running roughly northwest to southeast (the orientation shifts to east-west in Darjiling and Sikkim, southwest to northeast in Arunachal Pradesh, and north to south in Nagaland, Manipur and Mizoram), each with its own age, rock type and elevation band.

The Great Himalaya (Himadri) is the system's backbone: a continuous, permanently snow-covered range roughly 2,500 km long from east to west and 160 to 400 km wide, built of ancient crystalline and metamorphic rock. It carries the highest peaks on Earth, ten of the thirteen peaks above 8,000 m worldwide sit on this single range, among them Everest, Kanchenjunga and Nanga Parbat.

The Lesser Himalaya (Himachal) lies immediately south, a genuinely mountainous belt about 80 km wide, with peaks reaching roughly 4,500 m and valleys around 900 m, composed of highly compressed sedimentary and metamorphic rock. Three named ranges, the Pir Panjal, the Dhaola Dhar and the Nag Tibba, branch off the Great Himalaya into this belt, and it hosts both the Vale of Kashmir (a structural basin averaging about 1,600 m elevation, drained by the meandering Jhelum) and most of the well-known Himalayan hill stations.

The Shiwalik (Outer Himalaya) is the youngest and southernmost range, running almost the full length of the Himalaya (with small gaps in the east) and reaching a maximum width of about 100 km in Himachal Pradesh. Its southern edge sits at roughly the 275 m contour and rises another 760 m or so northward. Unlike the ranges to its north, the Shiwaliks are built from unconsolidated sand, gravel and conglomerate, sediment eroded straight off the rising Himalaya and deposited in front of it, which makes the range geologically the youngest part of the whole system even though it sits closest to the plains. Flat-floored basins called duns sit between the Shiwaliks and the Lesser Himalaya, the best known being Dehra Dun.

The Trans-Himalaya, to the north of the Great Himalaya, is generally grouped with the Tethys (or Tibetan) Himalaya and extends into Tibet; it is at its widest in Kashmir and Himachal Pradesh, forming the Spiti Basin and the Zanskar Range. Its rock is largely marine sedimentary material laid down in the Tethys Sea before the Himalaya rose, which is the opposite genetic story from the crystalline Great Himalaya immediately to its south, a useful pair to hold in mind since both sit north of the snow line but formed in entirely different ways. The Karakoram and Ladakh ranges belong to this northernmost belt and together form the water divide shutting the Indus system off from Central Asia.

The Northern Plains: An Alluvial Trench Between Two Old Blocks

The Northern Plain is not a landform in its own right so much as a fill: the geo-synclinal trench between the rigid Peninsular Block and the rising Himalaya, packed with sediment carried down by the Indus, the Ganga and the Brahmaputra over some 64 million years. It runs roughly 3,200 km east to west, 150 to 300 km wide, with alluvium up to 2,000 m deep in places, yet has a general surface elevation of only 50 to 150 m above sea level, essentially featureless once you are inside it.

From north to south the plain divides into recognisable belts. The Bhabar is a narrow, 8 to 10 km wide gravel apron right at the Shiwalik foothills, where streams coming off the mountains drop their coarse load and sometimes disappear underground. South of it, the Tarai is a 10 to 20 km belt where those streams re-emerge without a fixed channel, creating marshy, densely forested ground. South of the Tarai lie the older Bhangar and newer Khadar alluvium, the mature, depositional landscape of meanders, ox-bow lakes, braided channels and sandbars, with the Brahmaputra stretch particularly known for its shifting riverine islands. Haryana and Delhi sit on the water divide between the Indus and Ganga systems, and the Brahmaputra itself takes an almost 90-degree turn south at Dhubri before entering Bangladesh.

The Peninsular Plateau: An Ancient Block, Except Where Lava Buried It

The Peninsular Plateau is an irregular triangle rising from about 150 m at the plains' edge to 600 to 900 m, bounded by the Delhi Ridge (an Aravalli extension) in the northwest, the Rajmahal Hills in the east, the Gir Range in the west and the Cardamom Hills in the south, with a further detached extension in the northeast (the Shillong and Karbi Anglong plateaus). Structurally it splits into three groups: the Deccan Plateau, the Central Highlands and the Northeastern Plateau, and the single most important fact to hold about it is that most of this landmass is one of the oldest, most stable blocks on Earth, made of ancient gneiss and granite, except for the part buried under lava.

The Deccan Plateau, bordered by the Western Ghats, the Eastern Ghats and the Satpura-Maikal-Mahadeo hill line to the north, is largely built of the Deccan Traps: flood basalt that erupted in a series of massive lava flows from the late Cretaceous into the early Cenozoic, roughly 66 to 50 million years ago, ultimately covering some 500,000 sq km to a thickness exceeding 1,200 m. This is the origin of the black cotton soil that dominates the plateau's western and northwestern reaches, and it is a genuinely different rock story from the ancient crystalline gneiss and granite that makes up the rest of the Peninsular block, a distinction worth holding precisely: the Deccan is basaltic and comparatively young in geological terms, while the surrounding Peninsular crystalline rock is billions of years older.

The Western and Eastern Ghats border the Deccan Plateau on either side and are genuinely different mountains, not a matched pair despite the shared name. The Western Ghats (called the Sahyadri in Maharashtra, the Nilgiri Hills in Karnataka and Tamil Nadu, and the Anaimalai and Cardamom Hills in Kerala) are older than the Himalaya itself, form a continuous, roughly 1,600 km chain averaging about 1,500 m in elevation and rising further south, and are interrupted only once, by the 30 km Palghat Gap near 11 degrees north. Anaimudi (2,695 m), on the Anaimalai Hills, is the Peninsular Plateau's single highest point, followed by Dodabetta (2,637 m) on the Nilgiris; most Peninsular rivers rise here. The Eastern Ghats, by contrast, are discontinuous and low, cut into separate hill ranges (the Javadi, the Palkonda, the Nallamala, the Mahendragiri) by the very rivers, the Mahanadi, the Godavari, the Krishna and the Kaveri, that then run on to build deltas on the eastern coast. The two ranges meet only at the Nilgiri Hills.

The Central Highlands, bounded west by the Aravallis, sit north of the Deccan proper: the Satpura range forms a line of scarped plateaus at 600 to 900 m, a classic relict, highly denuded mountain rather than a young fold range, and the whole belt carries a general elevation of 700 to 1,000 m, sloping north and northeast, its rock showing genuine metamorphic history (marble, slate, gneiss). The Vindhyan and Kaimur ranges here feed most of the Yamuna's tributaries, and the Aravallis themselves contribute only one significant one, the Banas, to the Chambal. An eastern extension via the Rajmahal Hills leads into the mineral-rich Chotanagpur Plateau.

The Northeastern Plateau (the Meghalaya and Karbi Anglong plateaus) is, despite standing apart today, genuinely an extension of the same Peninsular block: a fault, generated by the northeastward push of the Indian Plate during Himalayan formation, opened a depression between the Rajmahal Hills and Meghalaya that later filled with river sediment and detached the two. Meghalaya itself splits into the Garo, Khasi and Jaintia Hills, is rich in coal, iron ore, sillimanite and uranium, and, because it catches the full force of the southwest monsoon, is so heavily eroded that Cherrapunji shows bare rock with almost no permanent vegetation cover despite the extreme rainfall.

One more physiographic fact worth flagging precisely because it is a trap: the Indian Desert (Marusthali), northwest of the Aravallis, is not a separate geological unit at all. Its underlying rock is the same Peninsular block, simply extended west and buried under wind-blown sand under extreme arid conditions; wood fossils near Jaisalmer, roughly 180 million years old, and marine deposits nearby indicate the region sat under the sea during the Mesozoic era before this desert surface formed.

The Coastal Plains: One Narrow, One Wide, for a Tectonic Reason

India's two coastal plains are shaped by opposite processes, and that single fact explains almost everything that differs between them. The western coastal plain is a submerged coast: geological evidence, including the belief that the ancient city of Dwarka now lies underwater off Gujarat, points to the coastline having gone under, which is exactly why it is narrow and why it drops off steeply enough to offer natural harbours (Kandla, Mumbai's JNPT/Nhava Sheva, Marmagao, Mangalore, Kochi). It runs from the Kachchh and Kathiawar coast in Gujarat through the Konkan coast in Maharashtra to the Goan and Malabar coasts further south, is narrowest in the middle and widens at both ends, carries no river deltas, and in Kerala develops the Malabar coast's distinctive kayals (lagoon backwaters), the setting for the annual Nehru Trophy boat race at Punnamada.

The eastern coastal plain is the opposite case, an emergent coast: broader throughout, it hosts the well-developed deltas of the Mahanadi, the Godavari, the Krishna and the Kaveri exactly because the rivers draining the older, gently east-tilted Peninsular block have had room and time to build them out. Because the coast is emergent rather than submerged, the continental shelf here extends up to 500 km out to sea, which makes deep natural harbours much harder to develop than on the west coast, so the eastern coast has fewer major ports despite being the wider plain.

The Islands: A Submerged Mountain Chain and a Coral Reef

India's two island groups could not have formed more differently, and that is really the whole exam-relevant point about them. The Andaman and Nicobar Islands, roughly 572 islands and islets in the Bay of Bengal, are the emerged crest of a submerged mountain arc, the above-sea continuation of the same mountain system that includes Myanmar's Rakhine (Arakan) range and the Patkai range to the north, running down toward the Mentawai Islands off Sumatra to the south. Their rock is largely sandstone, limestone and shale of Cenozoic age (formed within roughly the past 65 million years), consistent with a folded and uplifted mountain origin rather than volcanic construction, though a handful of the smaller islands genuinely are volcanic: Barren Island, in the group, is India's only active volcano. The Andaman group (north) and the Nicobar group (south) are separated by the Ten Degree Channel, and the highest points are Saddle Peak on North Andaman (738 m), Mount Thuiller on Great Nicobar (642 m), Mount Diavolo on Middle Andaman (515 m) and Mount Koyob on South Andaman (460 m).

Lakshadweep, by contrast, some 36 small islands (11 inhabited) in the Arabian Sea, 220 to 440 km off the Kerala coast, is built entirely of coral deposits, an atoll formation rather than a mountain remnant, with Minicoy as its largest island. The Nine Degree Channel splits the group, with Amini Island to its north and the Kavaratti/Cannanore cluster to its south, a name and a number (nine, not ten) that UPSC has used precisely to trip up anyone who has only half-learned the Andaman answer.

Matching a Place to Its Region: the Real Trap

Beyond the physical landforms, UPSC tests this chapter's cultural and regional geography almost entirely as place-to-region matching, and the trap is always a plausible-sounding wrong region, not an absurd one. Khajuraho genuinely sits in the Bundelkhand region of Madhya Pradesh, and Tirupati genuinely sits in the Rayalaseema region of Andhra Pradesh. But Bodhgaya is in Bihar, not in Madhya Pradesh's Baghelkhand region at all, and Shirdi, in Ahmednagar district, sits in western Maharashtra rather than the Vidarbha region, even though Baghelkhand and Vidarbha are both real, correctly-named regions elsewhere on the map. The only safe method is to fix each named place's actual state and district first, then check whether the region named alongside it is the one that place is actually in, rather than judging by how familiar or nearby the pairing sounds.

State Adjacency and Spread: Counting, Not Naming

A second recurring UPSC question type asks not which region a place sits in, but how many states a physical feature spans, or how many states you would cross travelling between two named places. The Western Ghats run through exactly six states, Gujarat, Maharashtra, Goa, Karnataka, Tamil Nadu and Kerala, a precise number confirmed by UNESCO's own inscription record for the range. The Himalaya, by contrast, spans considerably more than the "five states" a rushed answer might guess, its full stretch, from Jammu and Kashmir in the west through Himachal Pradesh, Uttarakhand and Sikkim to West Bengal and the northeastern states, runs across close to a dozen. Pulicat Lake, India's second largest brackish-water lagoon, sits almost entirely in Andhra Pradesh (about 96 percent of its area) with a small remainder in Tamil Nadu, so it is correctly described as spanning exactly two states even though the split is very lopsided. These "how many" questions cannot be answered from a mental map alone; they reward having actually counted the states a range or lake genuinely touches, rather than recalling only its most famous stretch.

Quick revision points

• Three geological regions: the ancient, rigid Peninsular Block (gneiss and granite, stable since the Cambrian); the young, actively folding Himalaya and other Peninsular mountains; the Indo-Ganga-Brahmaputra Plain, a filled geo-synclinal trench between them.
• Six physiographic divisions: Northern and North-eastern Mountains, Northern Plain, Peninsular Plateau, Indian Desert, Coastal Plains, Islands.
• Himalaya, north to south: Trans-Himalaya (Tethys sediment, Karakoram and Ladakh ranges), Great Himalaya/Himadri (crystalline, backbone, ten of the world's thirteen highest peaks), Lesser Himalaya/Himachal (Pir Panjal, Dhaola Dhar, Nag Tibba; Vale of Kashmir), Shiwalik/Outer Himalaya (youngest rock, unconsolidated sediment, duns like Dehra Dun).
• Northern Plain divides Bhabar (gravel apron) to Tarai (marshy re-emergence belt) to Bhangar (older alluvium) and Khadar (newer alluvium).
• Deccan Plateau = basaltic lava flows (Deccan Traps, roughly 66 to 50 million years old); the rest of the Peninsular block = far older crystalline gneiss and granite. Western Ghats are older than the Himalaya, continuous, six states; Eastern Ghats are discontinuous, low, river-cut. The two meet only at the Nilgiris.
• Indian Desert (Marusthali) is not a separate geological unit, it is the Peninsular block extended and sand-buried.
• Western coast: submerged, narrow, natural harbours, no deltas, Kerala's kayals. Eastern coast: emergent, broad, major deltas, fewer natural harbours because the continental shelf runs out to 500 km.
• Andaman and Nicobar: submerged mountain-arc extension (Rakhine to Patkai to Mentawai), Cenozoic sedimentary rock, Ten Degree Channel divides Andaman from Nicobar, Barren Island is India's only active volcano. Lakshadweep: coral atoll islands, Nine Degree Channel divides Amini from the Kavaratti cluster.
• Matching-pair trap: Khajuraho, Bundelkhand (correct); Tirupati, Rayalaseema (correct); Bodhgaya is in Bihar, not Baghelkhand; Shirdi is in western Maharashtra, not Vidarbha.
• State-count trap: Western Ghats, six states. Himalaya, well beyond five states. Pulicat Lake, two states (Andhra Pradesh and Tamil Nadu), despite a roughly 96-4 split.

The physical facts (rock type, age, formation process) and the regional facts (which place sits in which region, how many states a feature spans) are tested as two different question styles, so revise them as two separate checklists rather than one blended list of names.