Structure & Physiography — Himalayas, Plains, Peninsula, Coasts, Islands (UPSC Geography)

The Three Geological Divisions

🎯 Exam priority: High-yield (T1). The single heaviest-weighted Prelims chapter in this entire playlist. Learn the three geological divisions and six physiographic divisions as a genuine mental map, not a list to memorise — nearly every fact below has appeared, in some form, in a real question.

India isn't one landmass geologically — it's three genuinely different pieces of Earth's crust, stitched together over tens of millions of years, and every one of its physical features traces back to which piece it sits on.

The Three Geological Divisions

• The Peninsular Block is India's oldest, most rigid landmass — a great complex of ancient gneisses and granites that has stood essentially unchanged since the Cambrian period, with one major exception: part of its western coast has submerged beneath the sea due to tectonic activity. Its northern boundary runs irregularly from Kachchh along the Aravali Range's western flank near Delhi, then roughly parallel to the Yamuna and Ganga to the Rajmahal Hills; the Karbi Anglong and Meghalaya Plateau (northeast) and Rajasthan (west) are further extensions. As part of the Indo-Australian Plate, it has undergone vertical movements and block faulting, producing rift valleys (Narmada, Tapi, Mahanadi) and the Satpura block mountains, plus a set of relict, highly denuded residual ranges — the Aravali, Nallamala, Javadi, Veliconda and Mahendragiri hills among them. Because it is old and stable, its river valleys are characteristically shallow with low gradients — not the deep, V-shaped valleys of young mountain terrain.

• The Himalayas and other Peninsular mountains are, by contrast, young, weak and geologically flexible — still actively shaped by tectonic forces into faults, folds and thrust planes, and dissected by fast-flowing, youthful-stage rivers that carve gorges, V-shaped valleys, rapids and waterfalls.

• The Indo-Ganga-Brahmaputra Plain began as a geo-synclinal depression that reached its maximum development around 64 million years ago, during the third phase of Himalayan mountain formation. It has since been steadily filled by sediment from both Himalayan and Peninsular rivers, building alluvial deposits 1,000-2,000 m deep.

The Northern & North-Eastern Mountains

Follow the Himalayas across India and their orientation itself keeps changing — a detail examiners love precisely because it's so easy to memorise wrong.

The Northern & North-Eastern Mountains

• The Himalayas consist of a series of parallel ranges, including the Greater Himalayan range (the Great Himalayas plus the Shiwalik) — the "central axial range," running about 2,500 km east to west with a width of 160-400 km north to south. Crucially, this alignment is not uniform across the country: it runs northwest-southeast in India's northwestern parts, east-west through Darjiling and Sikkim, southwest-northeast in Arunachal Pradesh, and north-south through Nagaland, Manipur and Mizoram.

• This shifting alignment is exactly why the Himalayas function as more than a physical wall — they are simultaneously a climatic, drainage and cultural divide, each effect flowing directly from how the range is oriented relative to incoming monsoon winds and river systems at each stretch.

The Northern Plains

Beneath the flat, unremarkable surface of North India's plains lies a precisely layered structure — one that a farmer, a hydrologist and an examiner would each read completely differently.

The Northern Plains

• Formed by alluvial deposits from the Indus, Ganga and Brahmaputra, the Northern Plains stretch roughly 3,200 km east to west with an average width of 150-300 km and alluvium up to 1,000-2,000 m deep. From north to south they divide into three zones: the Bhabar (a narrow 8-10 km belt at the Shiwalik foothills, where streams deposit coarse rock and boulder material and often vanish underground), the Tarai (10-20 km wide, where these streams re-emerge without a defined channel, creating marshy, wildlife-rich wetlands), and the alluvial plains proper — split into older Bhangar and newer Khadar deposits, showing mature fluvial features like meanders, ox-bow lakes and braided channels.

• Haryana and Delhi form the water divide between the Indus and Ganga systems. The Brahmaputra, unusually, flows southwest from the northeast before making an almost 90° turn southward at Dhubri just before entering Bangladesh; its plains are noted for riverine islands and sand bars. The plains' general elevation is a modest 50-150 m above sea level, and their fertile alluvium supports wheat, rice, sugarcane and jute — and, in turn, an enormous population. The Sunderbans delta, formed at the Ganga-Brahmaputra mouth, is among the largest deltas in the world.

The Peninsular Plateau

South of the plains, India stands on some of the oldest, most weathered rock on the planet — a plateau so ancient it has watched entire mountain ranges rise and erode away beside it.

The Peninsular Plateau

• Rising from about 150 m to an elevation of 600-900 m, the Peninsular Plateau is an irregular triangle 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 — India's oldest and most stable landmass, split into three broad groups.

• The Deccan Plateau is bordered by the Western Ghats (known locally as the Sahyadri in Maharashtra, the Nilgiri hills in Karnataka/Tamil Nadu, and the Anaimalai and Cardamom hills in Kerala) and the Eastern Ghats, meeting at the Nilgiri hills. The Western Ghats are higher and far more continuous — averaging ~1,500 m and rising north to south — and host the Peninsula's two highest peaks: Anaimudi (2,695 m, Anaimalai hills) and Dodabetta (2,637 m, Nilgiri hills). Most Peninsular rivers originate here. The discontinuous, heavily eroded Eastern Ghats (Javadi, Palconda, Nallamala, Mahendragiri hills) are cut through by the Mahanadi, Godavari, Krishna and Kaveri.

• The Central Highlands, bounded west by the Aravali range, include the scarped Satpura range (600-900 m, a classic relict, highly denuded mountain forming the Deccan's northern boundary) and extend west to Jaisalmer's longitudinal dunes and barchans. Most Yamuna tributaries rise in the Vindhyan and Kaimur ranges; the mineral-rich Chotanagpur plateau forms this block's eastern extension.

• The Northeastern Plateau — the Meghalaya and Karbi Anglong plateau — is a genuine geological orphan: a huge fault, created by the Indian plate's northeastward push during Himalayan formation, later filled by river deposits, leaving it detached from the main Peninsular Block. Meghalaya subdivides into the Garo, Khasi and Jaintia Hills (named for their tribal inhabitants), rich in coal, iron ore, sillimanite, limestone and uranium; heavy southwest-monsoon rainfall has eroded it into the bare rocky surface famously seen at Cherrapunji.

The Indian Desert & the Coastal Plains

Travel from India's driest patch to its wettest coastlines and you cross two of the starkest physical contrasts the subcontinent has to offer.

The Indian Desert & the Coastal Plains

• Northwest of the Aravalis lies the Indian Desert, or Marusthali — undulating terrain of longitudinal dunes and crescent-shaped barchans, receiving under 150 mm of rain a year. Remarkably, this arid land was under the sea during the Mesozoic era — evidenced by ~180-million-year-old wood fossils at Aakal and marine deposits near Brahmsar, Jaisalmer. Though its underlying rock is an extension of the Peninsular plateau, wind and weathering have carved its surface into mushroom rocks, shifting dunes and oases; most rivers here are ephemeral (the Luni is the significant exception), often vanishing into brackish, salt-yielding playa lakes.

• India's coastline splits into two starkly different plains. The western coastal plain is an example of a submerged coast (the legendary city of Dwaraka is said to lie submerged along it) — narrow, but naturally suited to ports (Kandla, Mazagaon, JNPT, Marmagao, Mangalore, Cochin), running from Gujarat's Kachchh/Kathiawar coast through Maharashtra's Konkan coast to Karnataka/Kerala's Malabar coast. Its rivers form no deltas; Kerala's Malabar coast is instead known for its Kayals (backwaters), used for fishing, navigation and tourism — including the annual Nehru Trophy Vallamkali boat race at Punnamada Kayal.

• The broader eastern coastal plain, by contrast, is an emergent coast with well-developed deltas (Mahanadi, Godavari, Krishna, Kaveri) but far fewer natural ports — its continental shelf extends up to 500 km out to sea, complicating harbour development.

The Islands

Far out in two different seas, India holds island chains that could hardly be more geologically different from one another.

The Islands

• The Andaman & Nicobar Islands in the Bay of Bengal comprise roughly 572 islands and islets (~6°N-14°N, 92°E-94°E), split into the Andaman group (north) and Nicobar group (south), separated by the Ten Degree Channel. Believed to be an elevated stretch of submarine mountains, with some smaller islands of volcanic origin, this group is home to Barren Island — India's only confirmed active volcano, part of the Andaman group, roughly 138 km northeast of Port Blair. Key peaks include Saddle Peak (North Andaman, 738 m, the group's highest), Mount Diavolo, Mount Koyob and Mount Thuiller. These islands see convectional rainfall and equatorial-type vegetation, and were among the areas devastated by the 26 December 2004 Indian Ocean earthquake and tsunami.

• The Lakshadweep & Minicoy islands in the Arabian Sea (~8°N-12°N, 71°E-74°E, 280-480 km off Kerala) are, geologically, an entirely different story: the whole group of roughly 36 islands (11 inhabited) is built of coral deposits — true atolls, not submerged mountain-tops. Minicoy, the largest at 453 sq. km, is separated from the rest of the archipelago by the Nine Degree Channel; the Eleven Degree Channel further divides the archipelago's own northern and southern island groups. Storm beaches of unconsolidated pebbles, shingles and boulders line the eastern seaboard of these low coral islands.

Further Reading

• Standard NCERT-level geography textbooks and reference books, plus a good atlas (any UPSC reading list).

Why UPSC Asks This

• Peninsular Block questions test whether you know it's OLD and STABLE — shallow river valleys, not deep V-shaped ones, are the tell that a statement about it is wrong.

• Never assume a single Himalayan "alignment" — its direction genuinely changes region by region, and that shift is precisely why its climatic and drainage effects differ by stretch.

• Keep the western (submerged, few deltas, many ports) versus eastern (emergent, many deltas, few ports) coastal contrast crisp — it's a natural two-column comparison UPSC likes to test both ways.

Test Yourself: Practice Questions & PYQs

Structure & Physiography practice — the three geological divisions, the Himalayas' shifting alignment, the Northern Plains' zones, the Peninsular Plateau's three groups, the desert and coastal-plain contrast, and the islands. Then two real Prelims PYQs, including one from this year's own paper.

Practice Questions

Q1. Which geological division of India is characterised by ancient gneisses and granites, and has remained a broadly rigid block since the Cambrian period?

• (a) The Peninsular Block

• (b) The Indo-Ganga-Brahmaputra Plain

• (c) The Indian Desert

• (d) The Himalayas

Q2. The Indo-Ganga-Brahmaputra Plain originated as a geo-synclinal depression that reached maximum development approximately how long ago?

• (a) 64 million years ago

• (b) 640 million years ago

• (c) 1.4 million years ago

• (d) 6.4 million years ago

Q3. In which part of India does the Himalayan range run in an east-west direction?

• (a) The northwestern part of India

• (b) Nagaland, Manipur and Mizoram

• (c) Darjiling and Sikkim

• (d) Arunachal Pradesh

Q4. The 'Bhabar' belt of India's Northern Plains is best described as:

• (a) A region of braided channels and ox-bow lakes

• (b) A narrow belt at the Shiwalik foothills where streams deposit coarse rock and boulder material and often disappear

• (c) The zone of oldest alluvium furthest from active rivers

• (d) A swampy zone where underground streams re-emerge

Q5. The Brahmaputra river takes an almost 90° turn southward at which town before entering Bangladesh?

• (a) Siliguri

• (b) Dhubri

• (c) Guwahati

• (d) Dibrugarh

Q6. Which range forms the northernmost boundary of the Deccan Plateau and is a classic example of a highly denuded relict mountain?

• (a) The Eastern Ghats

• (b) The Aravali range

• (c) The Vindhyan range

• (d) The Satpura range

Q7. India's western coastal plain is described as a 'submerged' coast mainly because:

• (a) Tectonic subsidence has submerged part of it beneath the sea, as with the legendary city of Dwaraka

• (b) It has more deltas than the eastern coast

• (c) It lies entirely below the Tropic of Cancer

• (d) It receives very little rainfall

Q8. The Lakshadweep archipelago's northern and southern island groups are separated by which channel, while a separate channel divides Minicoy from the rest of the archipelago?

• (a) Palk Strait divides north-south; Gulf of Mannar isolates Minicoy

• (b) Eleven Degree Channel divides north-south; Nine Degree Channel isolates Minicoy

• (c) Ten Degree Channel divides north-south; Eight Degree Channel isolates Minicoy

• (d) Nine Degree Channel divides north-south; Ten Degree Channel isolates Minicoy

UPSC Previous Year Questions (PYQs)

The 2026 Peninsular Block question tests precisely the kind of structural understanding this chapter builds — knowing the Peninsular Block's rivers have shallow, NOT deep V-shaped, valleys is what separates a correct answer from a plausible-sounding wrong one.

Q9. Which of the following geographical features or phenomena is/are associated with the Peninsular Block of India? 1. Submergence of parts of the western coast due to tectonic activity. 2. Presence of residual mountain ranges such as the Veliconda hills and Mahendragiri hills. 3. Deep, V-shaped river valleys formed by fast-flowing rivers.

• (a) 2 and 3

• (b) 1 only

• (c) 1 and 2

• (d) 1, 2 and 3

Q10. Consider the following statements: 1. The Barren Island volcano is an active volcano located in the Indian territory. 2. Barren Island lies about 140 km east of Great Nicobar. 3. The last time the Barren Island volcano erupted was in 1991 and it has remained inactive since then. Which of the statements given above is/are correct?

• (a) 2 and 3 only

• (b) 1 only

• (c) 1 and 3 only

• (d) 1, 2 and 3

Mains Practice Questions

Use these to frame full-length answers. You don't have to answer one exactly — they show the angles UPSC tests, so let them guide which points you cover.

• Briefly mention the alignment of major mountain ranges of the world and explain their impact on local weather conditions, with examples.

• Distinguish between the Peninsular Block and the Himalayas in terms of geological age, structure, and typical river-valley form.

• Explain the three-fold division of India's Northern Plains from north to south, and describe the landforms typical of each.

• Compare the western and eastern coastal plains of India in terms of their geomorphological origin, port development, and delta formation.

• Why is the Peninsular Plateau considered the oldest and most stable landmass of India despite showing signs of faulting and seismic activity?

UPSC Mains — Previous Years’ Questions on this topic (last 10 years)

These are the actual GS Mains questions UPSC has asked on this theme — real proof of how, and when, it is tested. Try to write a full answer to each.

• 2021: Briefly mention the alignment of major mountain ranges of the world and explain their impact on local weather conditions, with examples. (250 words, 15 marks)