Why this chapter matters for UPSC: Mountains, plateaus and plains are the basic units of geomorphology, and India has all three on a grand scale: the young Himalaya, the ancient Peninsular plateau and the alluvial Northern Plains. GS1 asks why fold mountains lie where they do and how mountains shape weather. This chapter was dropped from NCERT's rationalised 2023-24 edition; only a short account of India's physical divisions survives, in the new Chapter 6, "Our Country – India". BharatNotes keeps it because the ideas run through the whole geography syllabus.

Contemporary hook: On 7 February 2021 a disaster struck the Chamoli district of Uttarakhand. It was first widely called a glacial lake outburst flood, but the study published in Science (16 July 2021) found that "a massive rock and ice avalanche roared down a Himalayan valley, turning into a deadly debris flow", damaging two hydropower plants. The authors write that it highlights "the increasing risk in the Himalayas caused by increased warming and development".

🧠 First Principles — Read This First

NCERT begins with a surprise: the ground you are standing on is slowly moving. The Earth's surface is not the same everywhere, and its endless variety of landforms results from two processes:

  • The internal process raises and sinks the Earth's surface at many places.
  • The external process continuously wears down and rebuilds the land. Wearing away is erosion; rebuilding is deposition. Both are done by running water, ice and wind.

By elevation and slope, landforms fall into three groups: mountains, plateaus and plains. Each suits people differently: life is hard on mountains and easier on plains, which is why plains hold most of the world's people.

PART 1 — Quick Reference

Three Landforms (NCERT)

LandformNCERT definitionExamples
MountainAny natural elevation considerably higher than its surroundings, often with a small summit and broad base; a steep hill above 600 m is generally termed a mountainHimalayas, Alps, Andes
PlateauAn elevated, flat-topped table land standing above the surrounding area, with one or more steep sides; from a few hundred to several thousand metres highDeccan, East African, Western Australian, Tibet plateaus
PlainA large stretch of flat land, generally not more than 200 m above mean sea level; mostly formed by riversGanga–Brahmaputra plains, Yangtze plains

Three Types of Mountains (NCERT)

TypeHow it formsNCERT examples
Fold mountainsLayers of rock are pushed from the sides and folded upwardYoung: Himalayas, Alps (rugged, high conical peaks). Old: Aravali (worn down), Appalachians, Urals (rounded, low)
Block mountainsLarge areas break and are displaced vertically: uplifted blocks are horsts, lowered blocks grabensRhine valley and Vosges mountains (Europe)
Volcanic mountainsBuilt by volcanic activityMt Kilimanjaro (Africa), Mt Fujiyama (Japan)

Record-Holders in NCERT

FeatureNCERT fact
Mauna Kea (Hawaii)An undersea mountain, 10,205 m high, higher than Mount Everest (8,848 m in NCERT; 8,848.86 m as announced by China and Nepal in December 2020)
Tibet plateauThe highest plateau in the world, 4,000–6,000 m above mean sea level
Deccan plateauOne of the oldest plateaus
Aravali rangeOne of the oldest fold mountain systems in the world

PART 2 — Concepts & Narrative

Mountains

Key Term

Mountain: a natural elevation of the Earth's surface, considerably higher than the surrounding area. Some rise above the clouds; some cannot be seen because they are under the sea. As you go higher, the climate becomes colder, and some mountains carry permanently frozen rivers of ice, called glaciers.

Range: mountains arranged in a line. Many mountain systems are series of parallel ranges extending over hundreds of kilometres: the Himalayas in Asia, the Alps in Europe and the Andes in South America.

Why few people live on mountains: the climate is harsh and the slopes are steep, so little land is available for farming.

NCERT's paper-mountain activity. Put a pile of paper on a table and push it from both sides: the sheets fold and rise into a peak. In the same way, NCERT says, the Himalayas and the Alps were formed.

Three types of mountains (NCERT)A tree diagram of the three types of mountains in NCERT. Mountains are natural elevations; a steep hill above 600 metres is termed a mountain. Fold mountains are young, such as the Himalayas and the Alps, rugged with high conical peaks, or old, such as the Aravali, the Appalachians and the Urals, worn down and rounded. Block mountains form when land breaks and moves vertically: raised blocks are horsts and lowered blocks grabens, as in the Rhine valley and the Vosges. Volcanic mountains are built by volcanic activity, such as Kilimanjaro and Fujiyama. A note adds that in India the Narmada, Tapi and Mahanadi lie in rift valleys and the Satpura are block mountains.Three types of mountains (NCERT)Mountainsnatural elevations; a steep hill above 600 mFold mountainsYoung: Himalayas,Alpsrugged, with highconical peaksOld: Aravali,Appalachians, Uralsworn down androundedBlock mountainsraised blocks:horstslowered blocks:grabensRhine valley andthe VosgesVolcanic mountainsbuilt by volcanicactivityKilimanjaro,FujiyamaIndia (NCERT XI): Narmada, Tapi and Mahanadirift valleys; the Satpura block mountains
Source: NCERT Class VI, ch. 6 (dropped in 2023-24); the India note is from NCERT Class XI, India: Physical Environment, ch. 2.

How the Himalaya rose. The US Geological Survey tells the story. About 80 million years ago India lay roughly 6,400 km south of Asia, moving north at about 9 m a century. It collided with Asia about 40 to 50 million years ago, and its northward advance slowed by about half. Because both landmasses have about the same rock density, neither could sink beneath the other, so the crust piled up into the Himalaya and the Tibetan plateau. USGS's educational page says the Himalayas "continue to rise more than 1 cm a year". NCERT Class XI puts the length of the Great Himalayan range at about 2,500 km, and its width between 160 and 400 km.

India's old mountains. NCERT Class VI calls the Aravali one of the oldest fold mountain systems, now much worn down by erosion. NCERT Class XI adds that the Peninsula "mostly consists of relict and residual mountains", such as the Aravali, Nallamala, Javadi, Veliconda, Palkonda and Mahendragiri hills. UNESCO describes the Western Ghats as "older than the Himalaya mountains", a chain about 1,600 km long, broken only by the 30 km Palghat Gap; it was inscribed as a World Heritage Site in 2012.

Block mountains and rift valleys in India. NCERT Class XI names "the rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains" as examples of the faulting that shaped the Peninsula. NCERT Class VI places the Narmada and Tapi between the Vindhyas and the Satpuras, flowing west into the Arabian Sea.

Explainer

Why mountains matter (NCERT)

  • Water: mountains are a storehouse of water. Many rivers rise in mountain glaciers; reservoirs store the water for drinking, irrigation and hydro-electricity.
  • Farming: river valleys and terraces are ideal for crops.
  • Forests: a rich variety of flora and fauna; fuel, fodder, shelter, gum, raisins and other products.
  • Tourism and sport: scenic beauty; paragliding, hang gliding, river rafting and skiing.

Plateaus

Key Term

Plateau: an elevated, flat-topped table land, standing above the surrounding area, with one or more steep sides. Plateaus, like mountains, may be young or old.

Why plateaus are useful (NCERT):

  • They are rich in minerals, so many of the world's mining areas lie on plateaus. The African plateau is famous for gold and diamond mining; in India, huge reserves of iron, coal and manganese are found in the Chhotanagpur plateau.
  • Rivers falling from a height form waterfalls: the Hundru falls on the Subarnarekha in the Chhotanagpur plateau, and the Jog falls in Karnataka.
  • Lava plateaus are rich in fertile black soil, good for cultivation.
  • Many plateaus have scenic spots that attract tourists.

NCERT Class XI describes the Peninsular plateau as a series of plateaus, such as the Hazaribagh, Palamu, Ranchi, Malwa, Coimbatore and Karnataka plateaus, and calls it "one of the oldest and the most stable" landmasses of India, its general elevation falling from west to east, as the flow of its rivers shows.

Plains

Explainer

How plains form (NCERT). Rivers flow down mountain slopes and erode them, carry the eroded material forward, and deposit their load of stones, sand and silt along their courses and in their valleys. Plains are formed from these deposits.

Why people crowd onto plains: plains are generally very fertile; transport networks are easy to build; more flat land is available for houses and farms. So plains are the most thickly populated regions of the world. In India, the Indo-Gangetic plains are the most densely populated.

India's Northern Plains in more detail (NCERT Class XI). From north to south they divide into the Bhabar (a narrow belt of 8–10 km at the foot of the Shiwaliks, where rivers drop their heaviest load of rocks and boulders), the Tarai, and the alluvial plains, which split into the Khadar and the Bhangar. The plains stretch about 3,200 km east to west, and their alluvium is 1,000–2,000 m deep.

Landforms and People

NCERT ends with responsibility. People live on different landforms in different ways: it is easier to grow crops, build a house or a road on a plain than on a mountain. Natural calamities such as earthquakes, volcanic eruptions, storms and floods cause great loss of life and property, and awareness can lower the risk. We often use land wastefully, for example building houses on fertile farmland or throwing garbage on land and into water. The land is not only for our use: it is our duty to leave the Earth a better place for future generations. NCERT's box on the Swachh Bharat Mission links a healthy body to clean water, air and surroundings.

UPSC Connect

Young mountains, real hazards: Chamoli 2021

The disaster of 7 February 2021 in Chamoli, Uttarakhand, is the textbook case of hazard on steep, young slopes. Shugar and colleagues (Science, vol. 373, 16 July 2021) showed that it began as a massive rock and ice avalanche, which turned into a debris flow and damaged two hydropower plants; more than 200 people were killed or went missing. It was not a glacial lake outburst flood. The authors link the rising risk in the Himalaya to warming and development.

Barren Island in the Andaman and Nicobar group has the only active volcano in India (NCERT Class XI). Its recorded eruptions go back to 1787, and its current eruptive period began in December 2022: ash rose to 4.6 km on 1 May 2023, eruptions resumed on 30 July 2025, lava flowed down its north flank from mid-November 2025, and an ash plume was seen on 10 January 2026 (Smithsonian Global Volcanism Program).

PART 3 — UPSC Integration

The chapter's two processes, internal and external, are the core of geomorphology: internal forces build the Himalaya and the rift valleys of the Narmada and Tapi; running water, ice and wind wear them down and build the plains. The distribution of fold mountains along continental margins, the influence of mountain ranges on local weather and the landslide risk of the Himalaya are recurring GS1 questions. India's relief explains its human geography: the plains hold the densest populations, the plateau holds the minerals, and the mountains hold the water. Answers should name the process, the landform and an Indian example.

Exam Strategy

Prelims traps:

  • NCERT Class VI has three types of mountains: fold, block and volcanic. "Relict and residual" is NCERT Class XI's description of the Peninsula's old hills.
  • Aravali: one of the oldest fold mountain systems in the world, much eroded; not India's longest range.
  • Horst = uplifted block; graben = lowered block (rift valley). NCERT's example: the Rhine valley and the Vosges.
  • Mountain > 600 m (steep hill); plain ≤ 200 m above mean sea level.
  • Mauna Kea (10,205 m) is higher than Everest measured from its base under the sea.
  • Tibet: highest plateau (4,000–6,000 m). Deccan: one of the oldest plateaus.
  • Chhotanagpur plateau: iron, coal and manganese; Hundru falls on the Subarnarekha.
  • Chamoli 2021 was a rock and ice avalanche turned debris flow, not a glacial lake outburst.

Mains angle: Explain why fold mountains lie along continental margins, and how a mountain barrier changes the weather on either side.

Practice Questions

Practice (UPSC-pattern, not past papers). Real UPSC questions on this chapter are listed in the PYQ box above.

Prelims:

  1. According to NCERT, which of the following are examples of volcanic mountains?

    1. Mt Kilimanjaro
    2. Mt Fujiyama
    3. The Vosges
      Select the correct answer:
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

  2. In a block mountain, the lowered blocks are called:
    (a) horsts
    (b) grabens
    (c) anticlines
    (d) escarpments

  3. The Hundru falls are on which river?
    (a) Damodar
    (b) Subarnarekha
    (c) Narmada
    (d) Sharavati

  4. Which of the following is described by NCERT as the highest plateau in the world?
    (a) Deccan plateau
    (b) East African plateau
    (c) Tibet plateau
    (d) Western plateau of Australia

  5. Consider the following statements about the Northern Plains (NCERT Class XI):

    1. The Bhabar is a narrow belt at the foot of the Shiwaliks where rivers deposit heavy rocks and boulders.
    2. The alluvial plains are divided into the Khadar and the Bhangar.
    3. The depth of alluvium is less than 100 m.
      Which of the statements given above are correct?
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

  6. According to the US Geological Survey, India collided with Asia, beginning the rise of the Himalaya, about:
    (a) 200 million years ago
    (b) 120 million years ago
    (c) 40 to 50 million years ago
    (d) 5 million years ago

Mains:

  1. Why are the river plains of the world thickly populated while mountains are thinly populated? Explain with Indian examples. (150 words)

📦 Revision Capsule

Revision Capsule

Hard Facts

  • Two processes: internal (uplift and sinking) and external (erosion and deposition by water, ice and wind).
  • Mountains: > 600 m; fold (Himalayas, Alps; old: Aravali, Appalachians, Urals), block (horst and graben; Rhine–Vosges), volcanic (Kilimanjaro, Fujiyama).
  • Plateaus: table lands; Tibet highest (4,000–6,000 m); Deccan one of the oldest; minerals, waterfalls, black soil.
  • Plains: ≤ 200 m; formed by river deposits; most populated (Indo-Gangetic plains).
  • Mauna Kea 10,205 m, higher than Everest.
  • Himalaya: collision 40–50 million years ago (USGS); Great Himalayan range about 2,500 km (NCERT XI).

Core Concepts

  • Internal forces build relief; external forces wear it down and build plains.
  • Landforms decide how people live: mountains thinly peopled, plains crowded.
  • Use land carefully: it must be left better for future generations.

Confused Pairs

  • Horst (raised) vs graben (sunk)
  • Young fold (Himalayas, Alps) vs old fold (Aravali, Appalachians, Urals)
  • Khadar (new alluvium) vs Bhangar (old alluvium)
  • Plateau (raised flat top) vs plain (low flat land)

PYQ Pattern

  • Mains GS1 asked why fold mountains lie along continental margins (2014), how mountain ranges affect local weather (2021) and why the Himalayas are prone to landslides (2016). See the PYQ box.

Sources

Sources