Structure and Physiography

Why this chapter matters for UPSC: This is Chapter 2 (Unit II, "Physiography") of India: Physical Environment in the current rationalised NCERT (Reprint 2026-27). It divides India twice: first by geological structure into three divisions, then by relief into six physiographic divisions. Learn the details of each division (plain belts, plateau groups, Ghats, island channels) and be able to explain why the divisions behave differently, for example landslides in the Himalaya against the Western Ghats, and the absence of deltas on the west-flowing rivers.

Contemporary hook: The Indian plate is still moving north, and NCERT says the Himalayas are still subject to faulting and folding; the Himalaya is still rising by more than 1 cm a year (USGS, This Dynamic Earth). Every answer on Himalayan earthquakes and landslides starts from the structural contrast in this chapter.

🧠 First Principles — Read This First

Two words carry this chapter. Structure means what the land is made of and how its rocks are arranged: old hard crystalline rock, folded young rock, or loose river sediment. Physiography means the shape of the land you see: mountains, plains, plateaus, coasts. NCERT defines physiography as the outcome of three things together, structure, process and stage of development. The same kind of rock, worked on by different processes for different lengths of time, gives different landscapes.

India has three structural units. The Peninsular Block in the south is very old gneiss and granite. It has stood as a rigid block for hundreds of millions of years and has been worn down into plateaus and low, rounded hills. The Himalayas in the north are young. They are still being pushed up by the northward movement of the Indian plate, so they are high, steep and cut by fast rivers into gorges. Between the two lies the Indo-Ganga-Brahmaputra Plain. It began as a long depression in front of the rising mountains and has been filled with sediment brought down by rivers from both sides.

Think of a crumpled tablecloth pushed against a heavy book. The book is the Peninsula, the folds are the Himalaya, and the dip between them, where crumbs collect, is the plain.

NCERT then divides India by relief into six physiographic divisions: mountains, plain, plateau, desert, coastal plains and islands. Most UPSC questions on Indian relief ask either for a fact from one division or for a reason that goes back to structure.

PART 1 — Quick Reference

Table 1: The Indian Plate — NCERT Timeline

NCERT gives "around 60 million years ago" for the start of the Deccan eruptions. Uranium-lead dating of ash beds places the main pulses close to the Cretaceous–Paleogene boundary, about 66 million years ago (Schoene et al., Science 363, 2019). Use NCERT's figure in an NCERT-based question.

Table 2: Three Geological Divisions (NCERT)

Table 3: Six Physiographic Divisions (NCERT)

Table 4: The Himalayan Ranges (South to North)

The rationalised Class 11 text does not give range-wise heights or widths. The figures above are NCERT Class 9's.

Table 5: Highest Peaks (NCERT Class 9 table)

K2 (Godwin-Austen) in the Karakoram lies in the Gilgit-Baltistan area of the UT of Ladakh, Indian territory under Pakistan's illegal occupation; the NCERT Class 9 map exercise asks students to mark K2 on the outline map of India. NCERT's table also labels Namcha Barwa (7,756 m; NCERT Class 11, Ch 3, prints 7,755 m) "India"; the peak stands at the bend of the Tsangpo in Tibet (NCERT Class 11, Ch 3), so leave it out of lists of Indian peaks.

Table 6: The Northern Plain, North to South

NCERT Class 9 gives the Bhabar as "about 8 to 16 km" wide and the plain as 2,400 km long and 240–320 km broad over 7 lakh sq km. The Class 11 figures are 8–10 km, ~3,200 km and 150–300 km. Neither book says how its length is measured, so the two cannot be reconciled from the texts. If an objective question quotes one set, it is following one book; learn the Class 11 figures for this chapter and recognise the Class 9 ones.

Table 7: Western and Eastern Ghats

UNESCO's World Heritage listing describes the Western Ghats as running about 30–50 km inland for 1,600 km, "interrupted only by the 30 km Palghat Gap at around 11°N".

PART 2 — Concepts & Narrative

The Peninsular Block

Boundary. NCERT traces the northern edge of the block as an irregular line from Kachchh, along the western flank of the Aravali range near Delhi, then roughly parallel to the Yamuna and the Ganga as far as the Rajmahal hills and the Ganga delta. The Karbi Anglong and Meghalaya plateau in the north-east, and Rajasthan in the west, are extensions of the block. In Rajasthan, desert features overlie it. The north-eastern parts are separated from the Chotanagpur plateau by the Malda fault in West Bengal.

Rock and movement. The block is made essentially of very ancient gneisses and granites. Since the Cambrian it has stood as a rigid block, except for part of the western coast that is submerged beneath the sea and some areas changed by tectonic activity without disturbing the basement. As part of the Indo-Australian plate it has undergone vertical movements and block faulting. NCERT's examples are the rift valleys of the Narmada, the Tapi and the Mahanadi, and the Satpura block mountains.

Relief. The Peninsula consists mostly of relict and residual mountains: the Aravali hills, Nallamala hills, Javadi hills, Veliconda hills, Palkonda range and Mahendragiri hills. River valleys are shallow with low gradients. Most east-flowing rivers form deltas before entering the Bay of Bengal (Mahanadi, Krishna, Kaveri, Godavari).

The Himalayas and Other Peninsular Mountains

Unlike the rigid Peninsula, these mountains are young, weak and flexible in structure. They are still subject to endogenic and exogenic forces, which produce faults, folds and thrust planes. They are tectonic in origin and are cut by fast-flowing rivers in their youthful stage, which make gorges, V-shaped valleys, rapids and waterfalls.

Shape and orientation. The Himalaya is a series of parallel ranges. In the north-western part of India the ranges run north-west to south-east. In the Darjeeling and Sikkim region they run east-west, in Arunachal Pradesh south-west to north-east (NCERT's text prints "southwest to the northwest"), and in Nagaland, Manipur and Mizoram north-south. NCERT gives the Great Himalayan range, the central axial range, as about 2,500 km long east to west and 160–400 km wide north to south. NCERT Class 9 describes the arc as about 2,400 km, 400 km wide in Kashmir narrowing to 150 km in Arunachal Pradesh, with greater altitudinal variation in the eastern half.

A barrier and a divide. NCERT calls the Himalaya a wall between the Indian subcontinent and Central and East Asia, and a climatic, drainage and cultural divide as well as a physical barrier.

Regional divisions (river-bounded). NCERT Class 9 divides the range west to east by river valleys:

• Punjab Himalaya — between the Indus and the Satluj (regionally Kashmir Himalaya and Himachal Himalaya)
• Kumaon Himalaya — between the Satluj and the Kali
• Nepal Himalaya — between the Kali and the Teesta
• Assam Himalaya — between the Teesta and the Dihang

The Brahmaputra marks the eastern boundary of the Himalaya. Beyond the Dihang gorge the mountains bend sharply south as the Purvachal or eastern hills: the Patkai, Naga, Manipur and Mizo hills. These are mostly strong sandstones, densely forested, running as parallel ranges and valleys. The rationalised Class 11 text no longer carries these regional divisions.

The Indo-Ganga-Brahmaputra Plain

The third geological division is the plain built by the Indus, the Ganga and the Brahmaputra. NCERT describes it as originally a geosynclinal depression that reached its maximum development during the third phase of Himalayan mountain building, about 64 million years ago (NCERT's date, which sits oddly with the 40–50 million years its Fundamentals of Physical Geography gives for the India–Asia collision; see Table 1). Since then, sediment from both Himalayan and Peninsular rivers has gradually filled it. The average depth of the alluvium is 1,000–2,000 m.

Landforms and drainage on the plain. The alluvial plains show features of the mature stage of rivers: sand bars, meanders, ox-bow lakes and braided channels. The Brahmaputra plains are known for riverine islands and sand bars. Most areas flood periodically and rivers shift course. The river mouths form some of the world's largest deltas, such as the Sunderbans. Apart from these features the plain is nearly featureless, at a general elevation of 50–150 m above mean sea level.

Two facts NCERT singles out. Haryana and Delhi form the water divide between the Indus and Ganga river systems. The Brahmaputra flows north-east to south-west and then takes an almost 90° southward turn at Dhubri before entering Bangladesh. The fertile alluvial soil supports wheat, rice, sugarcane and jute, and therefore a large population.

The Peninsular Plateau

Rising from about 150 m above the river plains to 600–900 m, the plateau is an irregular triangle. Its outer limits are the Delhi ridge (an extension of the Aravalis) in the north-west, the Rajmahal hills in the east, the Gir range in the west and the Cardamom hills in the south. The Shillong and Karbi Anglong plateau extend it into the north-east. It is made of a series of patland plateaus: Hazaribagh, Palamu, Ranchi, Malwa, Coimbatore and Karnataka. NCERT calls it one of the oldest and most stable landmasses of India. Its general elevation falls from west to east, as the flow of its rivers shows.

Features. Tors, block mountains, rift valleys, spurs, bare rocky structures, series of hummocky hills, and wall-like quartzite dykes that offer natural sites for water storage. Black soil is prominent in the western and north-western parts. The plateau has gone through repeated phases of uplift and submergence, with crustal faulting and fractures. NCERT gives the Bhima fault special mention for its recurrent seismic activity. The north-west has a complex relief of ravines and gorges, such as the ravines of the Chambal, Bhind and Morena.

The Deccan Plateau. It is bordered by the Western Ghats in the west, the Eastern Ghats in the east, and the Satpura, Maikal range and Mahadeo hills in the north. Table 7 compares the two Ghats. Most Peninsular rivers rise in the Western Ghats. The Deccan Traps, lava flows of volcanic (igneous) origin, have weathered over time to form black soil (NCERT Class 9).

The Central Highlands. They are bounded on the west by the Aravali range. The Satpura range, a series of scarped plateaus on the south at 600–900 m, forms the northernmost boundary of the Deccan plateau. It is a classic relict mountain, highly denuded and discontinuous. The plateau extends westward as far as Jaisalmer, where longitudinal sand ridges and crescent-shaped dunes (barchans) cover it. Metamorphic rocks such as marble, slate and gneiss record the region's metamorphic history. The Central Highlands lie at 700–1,000 m and slope to the north and north-east. Most tributaries of the Yamuna rise in the Vindhyan and Kaimur ranges. The Banas is the only significant tributary of the Chambal that rises in the Aravalli in the west. The Rajmahal hills form the eastern extension. South of them, the Chotanagpur plateau holds a large reserve of minerals.

The North-eastern Plateau. This is an extension of the main Peninsular plateau. NCERT's account is that the force of the Indian plate's north-eastward movement during the Himalayan origin created a huge fault between the Rajmahal hills and the Meghalaya plateau. River deposits later filled the depression, so the Meghalaya and Karbi Anglong plateaus now stand detached from the main block. The Meghalaya plateau is divided into the Garo, Khasi and Jaintia hills, named after the tribal groups living there, and extends into the Karbi Anglong hills of Assam. Like Chotanagpur, it is rich in coal, iron ore, sillimanite, limestone and uranium. It receives very heavy rainfall from the south-west monsoon, so its surface is highly eroded. Cherrapunji shows a bare rocky surface without permanent vegetation cover.

The Indian Desert

North-west of the Aravali hills lies the Great Indian Desert, or Marusthali. It is a land of undulating topography with longitudinal dunes and barchans. Rainfall is below 150 mm a year, so the climate is arid with little vegetation.

• A former sea floor. NCERT says the region was under the sea during the Mesozoic era. The evidence is the wood fossils park at Aakal and marine deposits around Brahmsar, near Jaisalmer. The wood fossils are estimated to be about 180 million years old.
• Peninsular rock, desert surface. The underlying rock is an extension of the Peninsular plateau. Under extreme aridity, physical weathering and wind have carved its surface into mushroom rocks, shifting dunes and oases (mostly in the south).
• Two slopes. The northern part slopes towards Sindh and the southern part towards the Rann of Kachchh.
• Drainage. Most rivers are ephemeral. The Luni in the south is the significant one. Some streams vanish after a distance into a lake or playa, a case of inland drainage. The brackish lakes and playas are the main source of salt.

The Coastal Plains

Western coastal plain: submerged. NCERT treats it as a submerged coastal plain and cites the belief that the city of Dwaraka, once part of the mainland, now lies under water. Because of the submergence the plain is narrow, and it offers natural conditions for ports and harbours. NCERT lists Kandla, Mazagaon, JLN Port (Nhava Sheva), Marmagao, Mangalore and Cochin. From north to south its divisions are the Kachchh and Kathiawar coast (Gujarat), the Konkan coast (Maharashtra), the Goan coast, and the Malabar coast (Karnataka and Kerala). NCERT Class 9 names the stretch south of Goa the Kannad plain. The plain is narrow in the middle and broader to the north and south. Its rivers form no deltas. The Malabar coast has kayals (backwaters) used for fishing, inland navigation and tourism. The Nehru Trophy Vallamkali boat race is held every year in Punnamada Kayal, Kerala.

Eastern coastal plain: emergent. The eastern plain is broader and is an example of an emergent coast. It has well-developed deltas of the Mahanadi, Godavari, Krishna and Kaveri. NCERT Class 9 calls the northern part the Northern Circar and the southern part the Coromandel Coast. Because the coast is emergent it has fewer ports and harbours. The continental shelf extends up to 500 km into the sea, which makes good ports difficult to develop. Chilika Lake, south of the Mahanadi delta in Odisha, is described in NCERT Class 9 as the largest salt-water lake in India.

The Islands

Bay of Bengal group. About 572 islands and islets, roughly between 6°N–14°N and 92°E–94°E. The two principal groups of islets are Ritchie's archipelago and the Labyrinth island. The chain divides into the Andaman in the north and the Nicobar in the south, separated by the Ten Degree Channel. The islands are believed to be an elevated portion of submarine mountains, though some smaller islands are volcanic. Barren Island, India's only active volcano, is in this group. NCERT's peaks: Saddle Peak (North Andaman, 738 m), Mount Diavolo (Middle Andaman, 515 m), Mount Koyob (South Andaman, 460 m) and Mount Thuiller (Great Nicobar, 642 m). The coasts have some coral deposits and beaches. The islands receive convectional rainfall and carry equatorial vegetation. NCERT recalls the calamity of 26 December 2004, the Indian Ocean tsunami.

Arabian Sea group. Lakshadweep and Minicoy lie between 8°N–12°N and 71°E–74°E, 220–440 km off the Kerala coast. The whole group is built of coral deposits. There are 36 islands with a total area of 32 sq km; NCERT says 11 are inhabited, but the UT Administration counts ten. The Nine Degree Channel divides the group, with Amini island to its north and Cannanore island to its south. The eastern seaboard has storm beaches of unconsolidated pebbles, shingle, cobbles and boulders.

NCERT Class 11 states that Minicoy is the largest island "with an area of 453 sq. km". This cannot be right: NCERT Class 9 gives the whole Lakshadweep group an area of 32 sq km. Learn the 32 sq km figure for the group and treat 453 sq km as a printing error. Minicoy is not the largest island either: the UT Administration gives Andrott 4.90 sq km, the largest, and Minicoy 4.80 sq km.

PART 3 — UPSC Integration

Mains Frameworks

1. Structure → hazard. Young, active Himalaya (earthquakes, landslides) versus rigid Peninsula, which still has active faults (NCERT's Bhima fault).
2. Structure → resources. The Peninsular block holds mineral reserves (Chotanagpur; the Meghalaya plateau's coal, iron ore, sillimanite, limestone and uranium). The plain holds deep fertile alluvium. The Himalaya is the source of perennial rivers (Chapter 3).
3. Coast type → ports and deltas. Submerged west coast: natural harbours, no deltas. Emergent east coast: deltas, a wide shelf, fewer natural ports.

Exam Strategy

Prelims traps from this chapter

• Tarai lies north of the alluvial plains, between the Bhabar and the Bhangar/Khadar. It is not a southern belt.
• Bhabar 8–10 km and Tarai 10–20 km (Class 11) versus Bhabar 8–16 km (Class 9).
• Plain length about 3,200 km (Class 11) versus 2,400 km (Class 9); neither book says how it is measured. Alluvium 1,000–2,000 m deep.
• Three plateau groups: Deccan, Central Highlands and North-eastern Plateau. The Deccan is one part of the Peninsular plateau, not another name for it.
• Anaimudi (2,695 m) is on the Anaimalai hills; Dodabetta (2,637 m) is on the Nilgiri hills. NCERT asks this directly.
• Ten Degree Channel separates Andaman from Nicobar; Nine Degree Channel divides the Lakshadweep group.
• Barren Island is India's only active volcano.
• Siachen is a Karakoram glacier, not a Great Himalaya (Himadri) glacier.
• Lesser Himalaya hill stations (Shimla, Mussoorie, Nainital, Darjeeling) are not to be confused with the southern hill stations of Tamil Nadu such as Ooty and Kodaikanal, which NCERT Class 9 places in the Peninsular plateau section.
• Haryana–Delhi is the Indus–Ganga water divide; Dhubri is where the Brahmaputra turns south.

Mains question patterns

• "Why no deltas on the west coast?" Use submergence, short swift rivers, and rift troughs for the Narmada and Tapi.
• "Himalayan vs Western Ghats landslides." Contrast structure (young and active versus old escarpment), triggers (seismicity and cloudbursts versus intense monsoon rain on steep slopes), and human factors (roads and hydro projects versus plantations and quarrying).

Practice Questions

Practice (UPSC-pattern, not past papers). Questions 1 and 2 are NCERT's own exercise MCQs.

Prelims:

1. Which one of the water bodies separates the Andaman from the Nicobar?
   (a) 11° Channel
   (b) Gulf of Mannar
   (c) 10° Channel
   (d) Andaman Sea

2. On which of the following hill ranges is the Dodabetta peak situated?
   (a) Nilgiri hills
   (b) Anaimalai hills
   (c) Cardamom hills
   (d) Nallamala hills

3. With reference to the Northern Plain, consider the following statements: 1. In the Bhabar belt along the Shiwalik foothills, many streams disappear. 2. The Tarai lies to the south of the alluvial plains. 3. The Khadar is made of newer alluvium than the Bhangar. Which of the statements given above is/are correct?
   (a) 1 only
   (b) 1 and 3 only
   (c) 2 and 3 only
   (d) 1, 2 and 3
   The Tarai lies between the Bhabar and the alluvial plains.

4. Consider the following pairs (peak : hills): 1. Anaimudi : Anaimalai 2. Dodabetta : Nilgiri 3. Mahendragiri : Western Ghats. Which of the pairs given above are correctly matched?
   (a) 1 and 2 only
   (b) 2 and 3 only
   (c) 1 and 3 only
   (d) 1, 2 and 3
   Mahendragiri is in the Eastern Ghats, not the Western. NCERT Class 9 calls it the highest Eastern Ghats peak; other references give Arma Konda in Andhra Pradesh.

Mains (practice, NCERT Ex. 3, about 125 words each):

1. Make a comparison of the island groups of the Arabian Sea and the Bay of Bengal.
2. What are the important geomorphological features found in the river valley plains?
3. If you move from Badrinath to the Sunderbans delta along the course of the Ganga, what major geomorphological features will you come across?
4. Why are landslides more frequent in the Himalaya than in the Western Ghats? (practice)

Short answers (NCERT Ex. 2, about 30 words): a traveller to Lakshadweep would sail from the Malabar coast of Kerala, the nearest part of the western coastal plain (the islands lie 220–440 km off Kerala). India's cold desert lies in Ladakh, between the Great Himalaya and the Karakoram, with the Ladakh and Zaskar ranges. The western coastal plain has no deltas because it is a submerged coast with short, swift rivers, and the Narmada and Tapi flow in rift troughs.

📦 Revision Capsule

Sources

• NCERT, India: Physical Environment, Textbook for Class XI, Chapter 2 "Structure and Physiography", rationalised edition, Reprint 2026-27 — kegy102.pdf. Chapter 3 for Namcha Barwa and the Indo-Brahma river — kegy103.pdf.
• NCERT, Fundamentals of Physical Geography, Class XI, Chapter 4 "Distribution of Oceans and Continents", Reprint 2026-27 (movement of the Indian plate, Deccan Traps, tillite) — kegy204.pdf.
• NCERT, Contemporary India – I, Textbook for Class IX, Chapter 2 "Physical Features of India" (2019-20 reprint): Himalayan range heights and widths, peak table, regional divisions, Purvachal, Ghats elevations, Mahendragiri, coastal divisions, Lakshadweep area. Printed citation; consulted via a mirrored copy of the NCERT PDF.
• UNESCO World Heritage Centre, "Western Ghats" (inscribed 2012), Outstanding Universal Value statement — whc.unesco.org.
• PIB (Ministry of Home Affairs), "Maps of newly formed Union Territories of Jammu Kashmir and Ladakh, with the map of India", 2 Nov 2019, as reproduced by the High Commission of India, Lilongwe — hcililongwe.gov.in.
• B. Schoene et al., "U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction", Science 363 (6429): 862–866, 2019. Printed citation.
• Revised height of Mt Everest (8,848.86 m), joint Nepal–China announcement of 8 Dec 2020, Xinhua (Wayback copy) — xinhuanet.com.
• Akashvani News, "Har Shikhar Tiranga culminates with the successful K2 expedition", 28 May 2025 (Kanchenjunga, 8,586 m): newsonair.gov.in.
• USGS, This Dynamic Earth, "The Himalayas: two continents collide": pubs.usgs.gov.
• Administration of the UT of Lakshadweep, "About Lakshadweep" (36 islands, 32 sq km, ten inhabited): lakshadweep.gov.in; island pages Andrott (4.90 sq km) and Minicoy (4.80 sq km).