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Every NCERT book that matters for UPSC — open a book, then a chapter. Learn each chapter's concepts, then how UPSC tests them — with diagrams, flowcharts and the past questions to attempt.
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← Our Environment — all chaptersOur Changing Earth
Start here: why this chapter matters
In simple wordsThe ground under your feet feels fixed for ever — but it is not. Deep inside, the earth stirs slowly, pushing up mountains and now and then shaking the ground or bursting out as a volcano. On the surface, rain, rivers, waves, ice and wind keep scraping the land away and dropping it somewhere else. This chapter is about both kinds of change, and the landforms they leave.
This is Chapter 3 of Our Environment (Class 7 Geography): 8 pages (12–19). It introduces lithospheric plates and why they move, divides earth movements into endogenic and exogenic forces (Fig. 3.1), explains volcanoes (Fig. 3.2) and earthquakes (Fig. 3.3) with a case study of the Bhuj earthquake of 2001 and an earthquake-preparedness box, and then the major landforms made by rivers, sea waves, ice and wind (Figs 3.4–3.9). It has three activity boxes, a glossary, a ‘Word Origin’ box, three ‘Do you know?’ boxes, a ‘Let's do’, several photographs and six exercises ending in a crossword.
- Builds on gess202 (Inside Our Earth: crust, mantle, core, magma and the three rock families). Goes further in kegy203 (earthquake waves, shadow zones, magnitude vs intensity, volcano types), kegy204 (continental drift, sea-floor spreading, plate tectonics), kegy205 (geomorphic processes: weathering and mass movements) and kegy206 (landforms of running water, groundwater, glaciers, waves and wind — this chapter's landforms in full).
- Disasters: kegy106 (natural hazards and disaster management in India) and hess402 (landslides, the Kinnaur case).
- UPSC, honestly: Prelims tests the basics — the Richter scale (1979), what causes earthquakes (1981), meanders as a sign of a mature river (1990), mushroom rocks and wind erosion (1991), barkhans (1991), why west-flowing rivers have no deltas (2004), P and S waves (2023) and an ox-bow lake (2023). Mains: no deltas from Western Ghats rivers (GS1 2013), tectonic change of continents and oceans (GS1 2025), earthquake preparedness and vulnerability (GS3 2015, 2021) and coastal erosion (GS3 2022). We link 13; many other plate, earthquake and landform questions are already linked to three chapters.
| Word | What it means here |
|---|---|
| Lithospheric plates | Large and small rigid slabs of the lithosphere that carry continents and ocean floors |
| Endogenic / exogenic forces | Forces acting inside the earth / on its surface |
| Diastrophic forces | Slow endogenic forces that build mountains (folding, faulting) |
| Volcano | A vent (opening) in the crust through which molten material erupts suddenly |
| Earthquake | Vibrations of the earth's surface caused when plates move |
| Focus / epicentre | The place in the crust where the movement starts / the place on the surface above it |
| Seismograph / Richter scale | The machine that records earthquakes / the scale on which their magnitude is reported |
| Weathering | Breaking up of rocks on the earth's surface |
| Erosion / deposition | Wearing away of the land by water, wind and ice / laying down of the material they carry |
| Meander / ox-bow lake | A large bend of a river in a plain / a lake left when a meander loop is cut off |
| Flood plain / levee | Flat, fertile land built of flood sediments / a raised river bank |
| Distributary / delta | A stream branching off a river near the sea / land built from the sediment of all its mouths |
| Sea cave, arch, stack, cliff | Hollow in coastal rock / its roof left over open water / a wall-like pillar left when the roof falls / a near-vertical rocky coast |
| Moraine | Rocks, sand and silt deposited by a glacier |
| Mushroom rock / sand dune / loess | Desert rock worn narrow at the base / low hill of wind-blown sand / very fine wind-blown sand spread over large areas |
Reading the chapter opening (page 12)
- Header art: the cartoon sun over a blue band with the chapter number and title; a QR code (0762CH03) to NCERT's e-content.
- The page opens straight into the plates and the beaker activity (next section).
At a glance — the six ideas to carry away
- Lithospheric plates move slowly because hot material inside the earth circulates (the beaker activity). Endogenic = inside forces; exogenic = surface forces.
- Endogenic: sudden (earthquakes, volcanoes) and slow / diastrophic (building mountains). Exogenic: erosion and deposition by rivers, wind, sea waves, glaciers.
- Volcano = vent in the crust; parts: magma chamber, vent, crater, lava, gases and ash. Focus (where it starts) vs epicentre (surface above it).
- Waves: P (longitudinal), S (transverse), L (surface). Seismograph records; Richter scale: 7.0 = major. Bhuj: 26 January 2001.
- River: waterfall (hard over soft rock) → meanders → ox-bow lake; floods build flood plains and levees; near the sea distributaries and a delta.
- Sea: cave → arch → stack, cliff; deposits beaches. Ice: hollows → lakes; moraines. Wind: mushroom rocks, sand dunes, loess (China).
1. Lithospheric plates and why they move
In simple wordsWatch rice in a pot of boiling water: grains rise in the middle, roll across the top and sink at the sides, round and round. Rock deep inside the earth circulates in the same way, only millions of times more slowly — and the broken outer shell of the earth is dragged along on top, like a raft on the circulating water.
The lithosphere is broken into a number of lithospheric plates — several large and some small, rigid, irregular slabs that carry the continents and the ocean floor (glossary). They move very slowly — the book says ‘just a few millimetres each year’ — because of the movement of hot material inside the earth, which circulates as the beaker activity shows. The movement of the plates causes changes on the earth's surface.
Reading the beaker activity and the glossary (page 12)
- Activity: a small coloured paper pellet in a beaker half filled with water, heated on a tripod. Two small sketches show the beaker over a flame and a half-circle of red and yellow bands with arrows going up and round. The pellet rises with the warm water and sinks back with the cooler water. The point: heat sets up a circular flow — the book's model for the movement inside the earth.
- Glossary — lithospheric plates: several large and some small, rigid, irregularly shaped slabs that carry continents and the ocean floor.
| Plate boundary (Beyond NCERT †; kegy204) | Plates… | What happens — with examples |
|---|---|---|
| Divergent | move apart | magma rises and new crust forms — mid-ocean ridges (the Mid-Atlantic Ridge) |
| Convergent | move towards each other | one plate sinks or the crust crumples — fold mountains (the Himalaya, where the Indian plate meets the Eurasian plate), deep trenches, volcanoes |
| Transform | slide past each other | crust is neither made nor destroyed; strong earthquakes (the San Andreas fault, California) |
NCERT details to read carefully — plates
- Speed: ‘a few millimetres each year’ understates it — plates usually move a few centimetres a year, roughly as fast as fingernails grow † (kegy204 gives sea-floor spreading rates in cm per year).
- The book says ‘molten magma inside the earth moves in a circular manner’. The mantle is solid rock that flows very slowly when hot (kegy203: only the asthenosphere is partly molten); molten magma is local. Safe line: ‘slow convection currents in the mantle move the plates’.
- The glossary says the earth's crust consists of plates; strictly the plates are pieces of the lithosphere — crust plus uppermost mantle (the text itself says ‘the lithosphere is broken into plates’).
2. Endogenic and exogenic forces
In simple wordsImagine a sandcastle on a trampoline. Someone bouncing underneath pushes it up or shakes it apart — forces from inside. The wind and the waves wear it down and pile the sand elsewhere — forces from outside. The earth's surface is the result of both, working all the time.
Earth movements are divided by the forces that cause them. Forces acting in the interior of the earth are endogenic; forces working on the surface are exogenic (Fig. 3.1). Endogenic forces sometimes cause sudden movements and at other times slow ones. Sudden movements such as earthquakes and volcanoes cause mass destruction; the slow, diastrophic forces build mountains. Exogenic forces work through erosion and deposition by rivers, wind, sea waves and glaciers.
Reading Fig. 3.1, ‘Evolution of Landforms’, and the ‘Word Origin’ box (pages 12–13)
- Fig. 3.1: a pink panel with a box tree. ‘Earth movements’ splits into ‘Endogenic forces’ and ‘Exogenic forces’. Under endogenic: ‘Sudden forces’ (earthquake, volcano, landslides) and ‘Diastrophic forces’ (building mountains). Under exogenic: ‘Erosional and Depositional’ (river, wind, sea-waves, glaciers). The point: every landform is made by a force from inside or from outside. Redrawn as our tree above.
- Word Origin: endo (inside) and exo (outside) + genic (origin) give endogenic and exogenic.
NCERT details to read carefully — forces
- Landslides appear under sudden endogenic forces in Fig. 3.1. A landslide is mass movement under gravity — exogenic in Class 11 (kegy205) — though earthquakes often trigger it. Write ‘landslides are often triggered by earthquakes’.
- Exercise 2(iii): of volcano, folding and flood plain, the one caused by sudden movement is the volcano; folding is slow (diastrophic).
- Diastrophic forces = slow endogenic forces that fold, fault and lift the crust (kegy205: orogeny and epeirogeny).
3. Volcanoes
In simple wordsSqueeze a tube of toothpaste with the cap loose: the paste pushes up the narrow neck and oozes out of the top. Molten rock under great pressure does the same through a weak opening in the crust — that opening, and the mountain it builds, is a volcano.
A volcano is a vent (opening) in the earth's crust through which molten material erupts suddenly (Fig. 3.2). Molten rock gathers in a magma chamber, rises through the vent, and comes out of the crater as lava, with gases and ash. Volcanoes are a sudden endogenic movement.
Reading Fig. 3.2, ‘A Volcano’ (page 13)
- A cut-away cone of grey-and-black layers standing on a yellow crust over a brown mantle; a red magma chamber at the base feeds a red pipe and side branches up to the top. Labels: gases and ash (a plume above), crater, vent, lava (red streaks on the flank), crust, mantle, magma chamber. The point: magma stored below rises through a vent and erupts as lava, gas and ash. Redrawn as our cross-section above.
Beyond NCERT — volcanoes in brief
- Most volcanoes lie along plate boundaries — around the Pacific (the ‘Ring of Fire’) and along mid-ocean ridges — and a few over ‘hot spots’ such as Hawaii (kegy203, kegy204).
- Barren Island in the Andaman Sea is India's only active volcano (UPSC 2018 — on kegy203).
- Types by eruption — shield, composite, caldera, flood basalt (the Deccan Traps) — are in kegy203.
4. Earthquakes: focus, epicentre, waves and magnitude
In simple wordsBend a stick slowly: nothing happens, nothing happens — then snap! The sudden break sends a jolt up your arms. When plates grind past each other, rock bends and stores strain until it snaps; the jolt spreads out as waves and the ground shakes.
When the lithospheric plates move, the surface of the earth vibrates; the vibrations can travel all round the earth. These vibrations are earthquakes (Fig. 3.3). The place in the crust where the movement starts is the focus; the place on the surface above it is the epicentre. Vibrations travel outwards as waves; the greatest damage is usually closest to the epicentre, and the effect weakens with distance. A ‘Do you know?’ box names three kinds of waves: P (longitudinal), S (transverse) and L (surface) waves. Another box explains that an earthquake is recorded by a seismograph and its magnitude reported on the Richter scale: 2.0 or less is felt only a little; over 5.0 can cause damage from falling things; 6.0 or more is very strong; 7.0 is a major earthquake. Earthquakes cannot be predicted, but preparation can reduce their impact.
⤵ From moving plates to a shaking town
Plates movepushed by slow circulation inside the earth
Strain buildsrocks along a plate boundary bend instead of sliding
Sudden slip at the focusthe rock breaks and moves; energy is released
Waves spreadP, S and then L waves radiate in all directions
Shaking at the surfaceworst near the epicentre; recorded by seismographs everywhere
| Wave (book's box) | Kind (book) | Properties the box asks you to find (kegy203 †) |
|---|---|---|
| P waves | longitudinal | primary; fastest, arrive first; particles vibrate back and forth along the direction of travel; pass through solids, liquids and gases |
| S waves | transverse | secondary; arrive after P; particles vibrate at right angles to the direction of travel; pass through solids only (UPSC 2023) |
| L waves | surface | travel along the surface; arrive last; the most destructive |
Reading Fig. 3.3, the boiling-lid activity and the two ‘Do you know?’ boxes (pages 13–14)
- Fig. 3.3, ‘Origin of an Earthquake’: a cut-away block of brown crust with white rings spreading across its top surface and radiating lines inside; two red arrows on the surface point in opposite directions along a crack. Labels: plate boundary, epicentre (centre of the rings), seismic waves radiate out in all directions, and focus (deep inside, ‘where the earthquake occurs… the origin of the seismic energy’). The point: the break starts at depth and the waves spread out from there. Redrawn above.
- Activity: water boiled in a closed container shakes its lid; peas, a spoon and beads on the lid vibrate, roll and rattle. The point: energy from below makes the surface vibrate, as in an earthquake.
- ‘Do you know?’ — three wave types (p. 13), with the task of finding their properties: see the table above.
- ‘Do you know?’ — seismograph and Richter scale (p. 14), with a photograph of a seismograph (white drum-like instruments on a base). The point: earthquakes are measured, and 7.0 counts as major.
NCERT details to read carefully — earthquakes
- The text says vibrations travel outwards ‘from the epicentre’; Fig. 3.3 itself labels the focus as ‘the origin of the seismic energy’. Waves radiate from the focus; the epicentre is simply the surface point above it where shaking is usually strongest.
- ‘The strength of the earthquake decreases away from the centre’: the intensity (damage felt, Mercalli scale) decreases; the magnitude (energy, Richter) is one number for the whole quake (kegy203; UPSC 2001).
- The Richter scale is logarithmic: each step is 10 times the amplitude and about 32 times the energy, not 10 (UPSC 2006 — on kegy203). The book's ‘6.0 or higher… very strong’ corresponds to USGS's ‘strong’ (6–6.9); ‘7.0 major’ matches USGS's ‘major’ (7–7.9) †.
- The Richter scale measures earthquakes (UPSC 1979); the seismograph records them.
5. The Bhuj earthquake of 2001, and being prepared
In simple wordsA fire drill at school feels silly — until the day there is a fire, and everyone already knows the way out. Nobody can say when an earthquake will strike, but knowing where to shelter, and building houses that do not fall, saves most lives.
The book tells the Bhuj earthquake through seven newspaper headlines: a massive earthquake, 6.9 on the Richter scale, hit Bhuj on 26 January 2001; schools were worst affected (971 students and 31 teachers feared dead in collapsed school buildings); three days later relief was not reaching everyone; phone lines, water pipelines and power lines were knocked out; hundreds of fires started as charcoal cookers overturned; an emergency was declared in the quake zone; and the Chief Minister of Gujarat appealed to the Centre for financial help. A photograph shows a ruined multi-storey building in Gujarat (Fig. 3.3a). The book adds that earthquakes cannot be predicted, though some people watch animal behaviour — agitated fish, snakes coming to the surface — and gives an earthquake-preparedness box: take shelter under a kitchen counter, table or desk, or against an inside corner or wall; stay away from fireplaces, chimneys and windows, mirrors and picture frames that can shatter; and spread awareness.
| Headline (book's number) | What it says | Our order of events |
|---|---|---|
| 1 · Earthquake hits Bhuj | magnitude 6.9 (Richter), 26 January 2001 | 1st — the quake |
| 4 · Destruction of Bhuj | phone lines, water pipelines, power transmission lines knocked out | 2nd — at once |
| 5 · Fire in the city | hundreds of fires from overturned charcoal cookers | 2nd — at once |
| 2 · School worst affected | 971 students and 31 teachers feared dead (1,002 in all) | 3rd — the toll emerges |
| 6 · Emergency declared in quake zone | a state of emergency declared | 4th — official response |
| 7 · CM's appeal to the Centre | Gujarat seeks financial help | 5th — funds sought |
| 3 · Bhuj relief effort blighted | three days on, food, blankets and medicines not reaching everyone | 6th — three days later |
⤵ If the ground shakes in the middle of the school day (activity 2, p. 14)
Dropget down before the shaking knocks you down
Coverunder a sturdy desk or table, or against an inside wall; protect head and neck
Hold onstay put until the shaking stops; keep away from windows, glass, shelves
Get out calmlyby the planned route to the open assembly area; no lifts, no running on stairs
Stay outaftershocks can follow; wait for teachers' instructions
| Can earthquakes be predicted? (attributed; no verdict) | Who | Position |
|---|---|---|
| Watching animals | local practice described by the book | agitated fish and snakes coming out may signal a coming quake |
| The scientific position | the US Geological Survey and seismologists generally † | no reliable method yet predicts the time, place and size of an earthquake; animal reports are not consistent enough to use |
| What everyone does agree on | the book; India's NDMA guidelines † | preparation — safe buildings, drills, awareness — reduces the damage |
Reading Fig. 3.3a, the case-study collage, the activity and the preparedness box (page 14)
- Fig. 3.3a, ‘Destruction caused by an Earthquake in Gujarat’: a photograph of a tall apartment block with its lower floors crushed and rubble in front. The point: badly built multi-storey buildings collapse — the main killer in earthquakes.
- ‘Earthquake – A Case Study’: seven numbered headlines on a torn-paper newspaper background (summarised in the table above).
- Activity: arrange the headlines in order; and decide where you would go if a quake struck during school — outlines in the activities section.
- Earthquake Preparedness box: safe spots, places to stay away from, and being prepared.
NCERT details to read carefully — Bhuj
- Magnitude: the book's 6.9 is the Richter reading reported in India; the USGS gives a moment magnitude of 7.7 † — about 16 times more energy (asserted). Quote both with their sources, or ‘about 7.7 (USGS)’.
- Date: 26 January 2001 — Republic Day. The epicentre was in Kachchh (Kutch) district near Bhuj †. The death toll is reported very differently by different sources; the book gives only the school figures, which we keep as the book's.
- ‘Emergency declared’: in India ‘emergency’ has a constitutional meaning (Articles 352, 356, 360); none was proclaimed for the Bhuj quake † — read the headline as ‘a disaster situation was declared’.
- Animal behaviour is not a reliable prediction method — the book itself says earthquakes cannot be predicted.
Beyond NCERT — after Bhuj (bare facts)
- Gujarat set up the Gujarat State Disaster Management Authority in 2001 and passed a State disaster-management law in 2003.
- The Disaster Management Act, 2005 created the National Disaster Management Authority (NDMA), chaired by the Prime Minister, with State and District authorities; the NDMA has issued earthquake-management guidelines (kegy106).
- India's building code divides the country into seismic zones by hazard; Kachchh lies in the highest-hazard zone (kegy203, kegy106). UPSC Mains asked about India's earthquake preparedness (GS3 2015) and vulnerability (GS3 2021).
6. Weathering, erosion and the work of a river
In simple wordsPour a jug of water down a sand heap: it cuts a channel, carries sand away and dumps it at the bottom in a little fan. A river does exactly this over thousands of years — cutting in the hills, winding across the plains and building new land where it meets the sea.
Two processes keep wearing the landscape away. Weathering is the breaking up of rocks on the earth's surface. Erosion is the wearing away of the landscape by agents such as water, wind and ice. The eroded material is transported and eventually deposited; erosion and deposition together create landforms. Running water erodes the landscape. Where a river tumbles at a steep angle over very hard rocks or down a steep valley side, it forms a waterfall (Fig. 3.4). In the plain it twists and turns in large bends called meanders; erosion and deposition on the sides of a meander bring the ends of the loop closer until the loop is cut off as an ox-bow lake. When the river overflows its banks it floods the land around and lays down layers of fine soil — sediments — building a flat, fertile flood plain; the raised banks are levees (Fig. 3.5). Near the sea the river slows, breaks into streams called distributaries, each with its own mouth, and deposits its load; the sediment from all the mouths forms a delta (Fig. 3.6).
⤵ The exogenic sequence (p. 15)
Weatheringrocks on the surface break up
Erosionwater, wind and ice wear the land away
Transportthe agents carry the eroded material
Depositionthe material is laid down when the agent slows
Landformserosional (waterfall, cave) and depositional (delta, beach, dune)
⤵ A river from the hills to the sea (the book's landforms in order)
Hills: waterfallthe river falls over hard rock; softer rock is undercut
Plain: meanderslarge bends, eroded on one side and built up on the other
Ox-bow lakea meander loop cut off from the river
Floods: flood plain and leveesfine sediment spread over the land; raised banks
Coast: distributaries and deltathe slow river drops its load at many mouths
Reading Figs 3.4–3.6, the waterfall box and the ‘Let's do’ (pages 15–16)
- Fig. 3.4, ‘Waterfall’: a painted block of layered rock with a river pouring over its edge into a pool; labels ‘hard rock’ (the top layer) and ‘softer rock undercut by the power of the water’. The point: the hard cap makes the drop; the softer rock below is worn back.
- ‘Do you know?’ — waterfalls, with a photograph captioned ‘The Niagra falls’ (a broad, misty curtain of falling water): thousands of small falls; the highest is Angel Falls (Venezuela); others are Niagara Falls (Canada–USA border) and Victoria Falls (Zambia–Zimbabwe border).
- Fig. 3.5, ‘Features made by a river in a flood plain’: a bird's-eye painting of a blue river winding across green land, with labels flood plains, levees (along the banks), a crescent ox-bow lake beside the river, and a meander; brown patches mark deposits on the inner bends. Redrawn as our stages and cross-section.
- Fig. 3.6, ‘A Delta’: a block showing a main river splitting into many branching distributaries that fan out into the sea over a pale, sediment-built triangle. Redrawn as our generic schematic.
- Let's do: names of a few world rivers that form a delta — outline in the activities section.
NCERT details to read carefully — rivers
- Weathering breaks rock where it lies; erosion wears it away and moves it. Do not mix them up.
- Waterfall = erosional; ox-bow lake = both (made by erosion and deposition, cut off from the river); flood plain, levee, delta = depositional; meander = both.
- Meanders mark the mature (plain) stage of a river (UPSC 1990); V-shaped valleys and gorges mark the young stage (kegy206).
- West-flowing peninsular rivers (Narmada, Tapi) form estuaries, not deltas — they do carry sediment, but they are swift and the coast is tide-swept (UPSC 2004: A true, R false; Mains 2013).
- The caption spells ‘Niagra’; it is Niagara. Victoria Falls is on the Zambezi † (UPSC 2003).
Beyond NCERT — Indian examples
- Ox-bow lakes: Kanwar (Kabar) Taal in Begusarai, Bihar, was formed by the meandering of the Burhi Gandak (UPSC 2023) and became Bihar's first Ramsar site in 2020.
- Deltas: the Ganga–Brahmaputra (Sundarbans), Mahanadi, Godavari, Krishna and Kaveri on the east coast (kegy103).
- Levees are also built artificially as flood embankments — common along the Kosi and the Brahmaputra.
7. The work of sea waves
In simple wordsHit the same spot on a wall with a ball thousands of times and the plaster cracks, then chips, then a hole appears. Waves strike a rocky coast billions of times; they crack it, hollow it, punch through it and leave pillars standing in the sea — and drop the broken sand along quieter shores.
Erosion and deposition by sea waves make coastal landforms. Waves keep striking the rocks; cracks develop and widen into hollows called sea caves. As the cavities grow, only the roof remains, forming a sea arch. Further erosion breaks the roof, leaving only wall-like features called stacks. A steep rocky coast rising almost vertically above the sea is a sea cliff. Waves also deposit sediments along the shore, forming beaches (Fig. 3.7).
⤵ From crack to stack (Exercise 4-iii)
Waves strikeagain and again at the rocks of a headland
Cracksdevelop and become larger and wider
Sea cavea hollow worn into the rock
Sea archthe cave cuts through; only the roof remains
Stackthe roof falls; only a wall-like pillar is left
Reading Fig. 3.7, ‘Features made by sea waves’ (page 16)
- A painting of a blue sea with reddish rock masses: a dark hollow at the waterline of the left rock (sea cave), a rock with an opening right through it (sea arch), and a lone pillar standing apart in the water (stack). The point: the three are stages of one process of wave erosion. Redrawn as our sequence.
NCERT details to read carefully — the sea
- Of cliff, beach and sea cave, the one that is not erosional is the beach (depositional) — Exercise 2(i).
- The book describes the sea cliff after the stack, but cliffs are where the process begins: waves cut the cliff, and caves, arches and stacks form in it.
- Exercise 3 offers ‘(f) sea cliff’ as a distractor; beach matches ‘(a) sea shore’.
Beyond NCERT — coastal erosion in India
- Much of India's coastline is eroding; causes include waves and storms, sand mining, dams that trap river sediment, and ports and breakwaters that interrupt the drift of sand (kegy206). UPSC Mains GS3 2022 asked for its causes, effects and management techniques — sea walls, groynes, beach nourishment and mangrove belts.
8. The work of ice and wind
In simple wordsA bulldozer pushing slowly across a field scrapes the soil off and dumps a heap at the end of its run — that is a glacier. A sandblaster used to clean old buildings wears away stone with flying grit — that is desert wind, which works hardest close to the ground.
Glaciers are ‘rivers of ice’. They erode the landscape by bulldozing soil and stones to expose the solid rock below and carve out deep hollows, which fill with water as the ice melts to become lakes in the mountains. The material a glacier carries — rocks big and small, sand and silt — is deposited as glacial moraines (Fig. 3.8). In deserts the main agent of erosion and deposition is wind. Winds erode the lower part of a rock more than the upper part, leaving mushroom rocks with a narrow base and a wide top. Wind lifts sand and drops it in low hill-like heaps called sand dunes (Fig. 3.9). Very fine, light sand can be carried very far; deposited over large areas, it is loess — large deposits are found in China.
| Agent | Erosional landform (book) | Depositional landform (book) |
|---|---|---|
| River | waterfall | flood plain, levees, delta (meanders and ox-bow lakes: both) |
| Sea waves | sea cave, sea arch, stack, sea cliff | beach |
| Glacier | deep hollows (later mountain lakes) | moraine |
| Wind | mushroom rock | sand dune, loess |
Reading Fig. 3.8, ‘A Glacier’, and Fig. 3.9, ‘Sand Dunes’ (pages 16–17)
- Fig. 3.8: a photograph of a snow-covered mountain valley with a long white tongue of ice streaked by dark lines of rock debris flowing down between bare rocky slopes. The point: a glacier is a slow river of ice carrying rock with it — the dark lines are the material that ends up as moraine.
- Fig. 3.9: a photograph of tall golden dunes with wind-rippled faces and a line of camels small in the foreground. The point: wind piles sand into hills, on a huge scale.
NCERT details to read carefully — ice and wind
- The depositional feature of a glacier is a moraine (Exercise 2-ii), not a flood plain or a beach.
- Mushroom rocks are wind-eroded features of deserts (Exercise 2-iv; UPSC 1991 matched them with ‘wind erosion’). The base is worn most because wind carries the most sand close to the ground.
- Loess is fine wind-blown material (silt), deposited far from its source — China's Loess Plateau is the classic case.
- A barchan (barkhan) is a crescent-shaped dune † (UPSC 1991; kegy206) — the crossword's ‘crescent-shaped lake’ is something else, the ox-bow lake.
Activities and in-text questions — answer outlines
The three activity boxes, the ‘Let's do’, the wave-properties task and the dunes question.
Activity, page 12: Heat a beaker of water with a paper pellet in it. What do you observe, and what does it show?
The pellet rises with the warm water in the middle, moves across the top, and sinks with the cooler water at the sides — a circular flow (convection). Material inside the earth circulates in a similar, far slower way, and this drags the lithospheric plates along. (Strictly, the mantle is solid rock that creeps, not liquid magma.)
Activity, page 13: Boil water in a closed container with peas, a spoon and beads on the lid. What do you notice?
As the water boils the lid shakes; the objects vibrate, the beads roll off and the spoon rattles. Energy from below makes the surface vibrate — in the same way, energy released inside the earth makes the ground shake in an earthquake.
Do you know?, page 13: Find out the properties of P, S and L waves.
P (primary, longitudinal): fastest, arrive first; particles move back and forth along the direction of travel; pass through solids, liquids and gases. S (secondary, transverse): arrive next; particles move at right angles to the direction of travel; pass through solids only. L (surface): travel along the surface, arrive last and cause the most damage (kegy203).
Activity 1, page 14: Arrange the Bhuj headlines in the right sequence of their happening.
1 Earthquake hits Bhuj (26 January 2001) → 4 Destruction of Bhuj (phone, water, power lines) and 5 Fire in the city (overturned cookers) — immediate → 2 School worst affected (971 students, 31 teachers feared dead) → 6 Emergency declared in the quake zone → 7 CM's appeal to the Centre → 3 Relief effort blighted (three days after). Some steps overlap; justify your order by cause and effect.
Activity 2, page 14: If a quake suddenly shook in the middle of the school day, where would you go for safety?
Drop, cover and hold on: get under a sturdy desk or table, or against an inside wall, away from windows, glass, cupboards and hanging objects; protect your head. When the shaking stops, leave calmly by the planned route to an open assembly area away from buildings, walls and electric poles; do not use lifts or run on stairs; expect aftershocks.
Let's do, page 16: Find out the names of a few rivers of the world that form a delta.
Ganga–Brahmaputra (the world's largest delta, the Sundarbans), Nile (Egypt), Mississippi (USA), Mekong (Vietnam), Irrawaddy (Myanmar), Indus (Pakistan), and in India the Mahanadi, Godavari, Krishna and Kaveri.
Page 17: Have you ever visited a desert? Try to collect some pictures of sand dunes.
Collect pictures of the Thar (Jaisalmer's Sam dunes), the Sahara and the Arabian deserts; note the gentle windward slope and steep leeward slope, and crescent-shaped dunes (barchans). Label the wind direction on each.
NCERT exercise — answer outlines
Seven short answers, five ticks, a match, four reasons, a photograph activity and a crossword. Try first, then open.
1 (i) Why do the plates move?
Because of the movement of hot material inside the earth, which circulates in a circular way (as in the heated-beaker activity) and drags the lithospheric plates along — very slowly, a few millimetres (book) to a few centimetres a year.
1 (ii) What are exogenic and endogenic forces?
Endogenic forces act in the interior of the earth — sudden (earthquakes, volcanoes) or slow (diastrophic, building mountains). Exogenic forces work on the surface — erosion and deposition by rivers, wind, sea waves and glaciers.
1 (iii) What is erosion?
The wearing away of the landscape by agents such as water, wind and ice; the eroded material is carried away and later deposited, making landforms.
1 (iv) How are flood plains formed?
When a river overflows its banks it floods the land around and deposits layers of fine soil and other sediments; flood after flood, these build a flat, fertile flood plain, with raised banks (levees) along the river.
1 (v) What are sand dunes?
Low hill-like heaps of sand in deserts, formed when the wind, which lifts and carries sand, slows or stops and drops it.
1 (vi) How are beaches formed?
Sea waves deposit sand, pebbles and other sediments along the shore; these deposits form beaches — a depositional coastal landform.
1 (vii) What are ox bow lakes?
Crescent-shaped lakes formed when a meander loop is cut off from the river: erosion and deposition bring the ends of the loop closer until the river cuts across and leaves the loop as a lake (also called a cut-off lake).
2. Tick the correct answer: (i) not an erosional feature of sea waves; (ii) depositional feature of a glacier; (iii) caused by sudden movements of the earth; (iv) mushroom rocks are found in; (v) ox bow lakes are found in.
(i) (b) Beach. (ii) (c) Moraine. (iii) (a) Volcano. (iv) (a) Deserts. (v) (b) River valleys.
3. Match: (i) Glacier (ii) Meanders (iii) Beach (iv) Sand dunes (v) Waterfall (vi) Earthquake — with (a) Sea shore (b) Mushroom rock (c) River of ice (d) Rivers (e) Vibrations of earth (f) Sea cliff (g) Hard bed rock (h) Deserts.
(i) Glacier – (c) river of ice; (ii) Meanders – (d) rivers; (iii) Beach – (a) sea shore; (iv) Sand dunes – (h) deserts; (v) Waterfall – (g) hard bed rock; (vi) Earthquake – (e) vibrations of earth. Left over: (b) and (f).
4 (i) Give reasons: Some rocks have a shape of a mushroom.
In deserts the wind carries most of its sand close to the ground, so it wears away the lower part of a rock more than the upper part; the rock is left with a narrow base and a wide top — a mushroom rock.
4 (ii) Give reasons: Flood plains are very fertile.
Every flood spreads a fresh layer of fine sediment (silt), rich in plant nutrients, over the plain; the land is flat and well watered — so flood plains are among the most fertile farmlands (the Ganga plain).
4 (iii) Give reasons: Sea caves are turned into stacks.
Waves keep striking the cave; it grows until only its roof remains (a sea arch); further erosion breaks the roof and leaves only the wall-like side — a stack.
4 (iv) Give reasons: Buildings collapse due to earthquakes.
Earthquake waves — especially surface waves — shake the ground back and forth and up and down; buildings not designed for such forces (weak joints, heavy upper floors, poor materials) crack and fall. Shaking is strongest near the epicentre; soft ground can amplify it. Earthquake-resistant design and building codes prevent most collapses.
5. Activity: Identify the features in the three photographs and say whether each is erosional, depositional or both.
(1) A broad curtain of water falling over a rock ledge — waterfall, erosional. (2) A river winding in loops through forested land — meanders, both (erosion on the outer bank, deposition on the inner). (3) Flat green fields beside a line of trees — flood plain, depositional.
6. For fun: Solve the crossword.
Across: 2 MEANDER, 4 ICE, 7 GLACIER, 9 WATERFALL, 11 CAVE, 12 LEVEE, 13 SEA, 14 DESERT, 15 SAND DUNE, 16 FLOOD PLAIN. Down: 1 WAVE, 3 RIVER, 5 CLIFF, 6 MORAINE, 8 OX-BOW LAKE, 10 LOESS, 13 STACK, 14 DELTA. (Every crossing letter is checked against the grid in our file.)
Reading the exercise photographs and the crossword (pages 18–19)
- Exercise 5: a table with three small photographs — a wide, brown waterfall throwing up spray; an aerial view of a pale river looping through green forest; and flat green fields under a line of trees — and empty columns for the feature's name and type. Outline above.
- Exercise 6: a crossword grid with 10 across and 8 down clues, all from this chapter's words. Solution above.
Keys and slips to handle with care
- Stored UPSC keys linked here: 1979 (a earthquakes), 1981 (d faulting), 1990 (b meanders), 1991 barkhan (a crescent dune), 2004 (c: A true, R false), 2023 P and S waves (c both), 2023 lakes (b only two — Kolleru is fed by streams between the Krishna and Godavari deltas, not directly by the Krishna) are standard. 1991 match (mushroom rocks–wind erosion, Cape Verde–volcanic, Thar–low-latitude desert, Vosges–fold type): key (d) is the only option with mushroom rocks–wind erosion, but the Vosges are usually described as block (horst) mountains beside the Rhine rift valley, so the ‘fold type’ pair is disputed; answer by elimination. None of the pending key issues applies.
- Book slips with safe lines: ‘a few millimetres’ a year; ‘molten magma’ circulating; ‘the crust consists of plates’; landslides as endogenic; waves ‘from the epicentre’; ‘strength decreases’ (intensity); Bhuj 6.9 vs 7.7; ‘state of emergency’; animal behaviour as prediction; ‘Niagra’; cliff described last.
⤵ Answer frame for any landform question
Agentriver, sea waves, glacier or wind (or an endogenic force)
Processerosion, transport or deposition — and why here (hard rock, slowing water, sand near the ground)
Stagese.g. bend → loop → cut-off; crack → cave → arch → stack
Type and exampleerosional, depositional or both; an Indian example
Human anglefertile flood plains, deltas and coasts at risk; floods, erosion, earthquakes and preparedness
What to remember
Numbers
Chapterbook pp. 12–19 (8 PDF pages; QR code 0762CH03)
Plate speedbook: ‘a few millimetres a year’; usually a few centimetres a year †
Forces (Fig. 3.1)endogenic: sudden (earthquake, volcano, landslides*) + slow (building mountains); exogenic: river, wind, sea waves, glaciers
Parts of a volcanomagma chamber, vent, crater, lava, gases and ash
Earthquake waves3: P (longitudinal), S (transverse), L (surface)
Richter box≤ 2.0 felt a little; > 5.0 damage from falling things; ≥ 6.0 very strong; 7.0 major
Richter stepseach step: 10× amplitude, about 32× energy (kegy203)
Bhuj earthquake26 January 2001; 6.9 Richter (book) / 7.7 moment magnitude (USGS †)
Bhuj schools (book)971 students + 31 teachers = 1,002 feared dead
Bhuj case study7 headlines; relief problems 3 days after
Highest waterfallAngel Falls, Venezuela; Niagara (Canada–USA); Victoria (Zambia–Zimbabwe, on the Zambezi †)
River landformswaterfall → meander → ox-bow lake; flood plain, levees; distributaries, delta
Sea landformssea cave → sea arch → stack; sea cliff; beach
Glacier / windhollows → lakes, moraine / mushroom rock, sand dune, loess (China)
Crossword10 across + 8 down, 17 crossing cells
One-liners
- The lithosphere is broken into plates that move slowly because hot material inside the earth circulates.
- Endogenic forces work from inside the earth; exogenic forces work on its surface.
- Earthquakes and volcanoes are sudden endogenic movements; mountain building is slow.
- A volcano is a vent through which molten material erupts.
- The focus is where an earthquake starts; the epicentre is the point on the surface above it.
- A seismograph records earthquakes; their magnitude is reported on the Richter scale.
- Weathering breaks rocks; erosion wears them away and moves them; deposition lays them down.
- A meander loop cut off from the river becomes an ox-bow lake.
- Floods spread fine sediment that builds fertile flood plains and raised levees.
- Waves turn a sea cave into an arch and then a stack.
- Glaciers deposit moraines; wind makes mushroom rocks, dunes and loess.
Traps to avoid
- Plates usually move a few centimetres a year, not a few millimetres.
- The mantle is solid rock that creeps; it is not a sea of molten magma.
- Waves radiate from the focus, not from the epicentre.
- Intensity weakens with distance from the epicentre; magnitude is a single number for an earthquake.
- Landslides are mass movement under gravity, even if an earthquake triggers them.
- Bhuj 2001: 6.9 on the Richter scale (book) but 7.7 moment magnitude (USGS).
- A beach is depositional; cliffs, caves, arches and stacks are erosional.
- Folding is a slow movement; volcanoes and earthquakes are sudden.
- West-flowing peninsular rivers form estuaries, not deltas, even though they carry sediment.
- A barchan is a crescent-shaped sand dune; an ox-bow lake is a crescent-shaped lake.
How to strategise
Prelims — what UPSC asks
- From this chapter: the Richter scale measures earthquakes (1979), earthquakes from faulting of rocks (1981), meanders show a mature river (1990), mushroom rocks and wind erosion (1991), the barkhan as a crescent dune (1991), why west-flowing rivers have no deltas (2004), how P and S waves move (2023), and Kanwar Lake as a meander (ox-bow) lake (2023).
- Elsewhere: magnitude vs intensity (2001) and the logarithmic Richter scale (2006) on kegy203; the 1991 Garhwal earthquake (1992) on kegy203, kegy204 and iest102; Barren Island (2018) and volcano locations (1999, 2005) on kegy203; deltas and lakes (1983) on kegy206; waterfalls and their rivers (2024) on kegy103.
- Method: learn each landform with its agent and whether it is erosional or depositional; learn focus vs epicentre, P vs S, and magnitude vs intensity as pairs.
Mains — where it appears and how to answer
- From this chapter: GS1 2013 (no deltas from Western Ghats rivers) — delta formation and its conditions; GS1 2025 (tectonic movements changing continents and ocean basins) — the plates and endogenic forces, developed with kegy204; GS3 2015 and 2021 (earthquake preparedness and India's vulnerability) — the Bhuj case study and the preparedness box; GS3 2022 (coastal erosion) — the work of sea waves.
- Elsewhere: the 2004 tsunami (GS3 2017) and tsunamis (GS1 2025) on kegy203; fold mountains and plate margins (GS1 2014) and mantle plumes (GS1 2018) on kegy204.
- A labelled sketch earns marks — focus and epicentre, crack-to-stack, or meander to ox-bow. In disaster answers, give dates and magnitudes with their source (e.g. Bhuj, 26 January 2001, 7.7 USGS).
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. Why do the lithospheric plates move, according to the book?
2. Which of these is a slow endogenic movement?
3. The point on the surface directly above the place where an earthquake starts is the:
4. Which wave type is called transverse in the book's box?
5. The book gives the Bhuj earthquake of 26 January 2001 as 6.9 on the Richter scale; the USGS gives 7.7. Roughly how many times more energy does 7.7 imply?
6. Which landform is formed by deposition?
7. A crescent-shaped lake left beside a river in a plain is:
8. Mushroom rocks have a narrow base because:
UPSC questions from this chapter
Open any question to attempt it in the Question bank — your attempt is saved to your progress.