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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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← Fundamentals of Physical Geography — all chaptersLandforms and their Evolution
Start here: why this chapter matters
In simple wordsChapter 5 introduced the sculptors — running water, groundwater, glaciers, waves and wind. This chapter is the gallery of their sculptures. Each agent has a ‘signature’: rivers make V-shapes and deltas, ice makes U-shapes and moraines, waves make cliffs and spits, wind makes dunes. Learn the signature and you can read any landscape.
A landform is a small-to-medium tract of the earth's surface with its own shape, size and materials, made by particular processes and agents. Several related landforms make a landscape. Landforms change as processes continue, and when climate changes or the land is raised or lowered, the processes themselves change. So every landform has a history: a landmass passes through stages comparable to life — youth, maturity and old age.
- Builds on Chapter 5 (weathering, mass movement, erosion, deposition) — those processes, seen through five agents.
- Links to Indian physiography (Himalayan glaciers, Gangetic floodplains, east-coast deltas, west-coast cliffs, Thar dunes) and to Chapter 13 (waves and currents).
- UPSC: Prelims asks identification — eskers and drumlins, barchans, maturity signs, deltas, oxbow lakes, mangroves as buffers. Mains GS1 asked about fjords (2023), no deltas on Western Ghats rivers (2013) and aeolian processes in desertification (2026); GS3 asked coastal erosion (2022).
| Word | What it means here |
|---|---|
| Landform / landscape | One feature (a dune) / a set of related features (a desert) |
| Gradient | Steepness of slope; steep gradient → cutting down, gentle → depositing |
| Abrasion | Grinding of rock by the debris an agent carries |
| Peneplain | ‘Almost a plain’ — the end of long river erosion |
| Karst | Limestone landscape shaped by solution (named after the Karst region by the Adriatic) |
| Till / outwash | Unsorted debris dropped by ice / sorted, layered debris laid by meltwater |
| Moraine | Ridge of glacial till |
| Longshore current | Current flowing along the coast that carries sand sideways |
| Deflation | Wind lifting away dust and fine particles |
| Saltation | Grains moving in short hops |
NCERT's question: the two aspects of landform evolution(1) The transformation of a part of the earth's surface from one landform into another, and (2) the transformation of an individual landform after it has formed — both through stages over time.
At a glance — the six ideas to carry away
- Every landform has a history: youth → maturity → old age; running water ends in a peneplain with monadnocks.
- Rivers erode (gorge, canyon, potholes, incised meanders, terraces) and deposit (fans, deltas, levees, point bars, oxbow lakes).
- Karst = groundwater dissolving limestone: sinkholes, uvalas, lapies, caves, stalactites, stalagmites.
- Glaciers carve cirques, horns, arêtes, U-valleys, fjords; drop till (moraines, drumlins) and outwash (eskers, outwash plains).
- High rocky coasts show erosion (cliffs, stacks); low sedimentary coasts show deposition (bars, spits, lagoons).
- In deserts sheet floods and wind make pediments, inselbergs, playas, mushroom rocks and dunes.
1. Running water and the cycle of a landscape
In simple wordsPour water on a heap of soil in the garden. First it runs as a thin sheet, then gathers into tiny channels, which deepen into little gullies, which join into a valley system. Keep pouring for a very long time and the heap is worn almost flat. That is the story of a river landscape.
In humid regions, running water is the most important agent of degradation. It has two parts: overland flow as a sheet over the land, and linear flow as streams and rivers in valleys. Erosional landforms belong mostly to vigorous, youthful rivers on steep gradients; as gradients ease, rivers slow and deposit — the gentler the gradient, the greater the deposition. Down-cutting gives way to lateral erosion of the banks, and hills and valleys are reduced to plains.
⤵ From sheet flow to peneplain
Overland flow → sheet erosionwater removes surface material in the direction of flow
Rillssmall narrow channels where the flow concentrates
Gulliesrills deepen, widen and lengthen
Valley networkgullies join; early down-cutting removes waterfalls and cascades
Middle stage: lateral erosionvalley sides and divides are lowered
Peneplaina lowland of faint relief, with low resistant remnants — monadnocks
| Youth | Mature | Old | |
|---|---|---|---|
| Streams | Few, poorly integrated, on original slopes | Plenty, well integrated | Few small tributaries, gentle gradients |
| Valleys | Shallow V; no or very narrow floodplains | Still V but deep; wider floodplains on trunk streams; meanders within the valley | Streams meander freely over vast floodplains |
| Divides | Broad and flat, with marshes, swamps, lakes | Sharp; flat interfluves and swamps disappear | Broad and flat again, with lakes, swamps, marshes |
| Special features | Meanders on uplands may later entrench; waterfalls and rapids where hard rock is exposed | Waterfalls and rapids disappear | Natural levees, oxbow lakes; land at or slightly above sea level |
Beyond NCERTThis youth–maturity–old-age scheme is W. M. Davis's ‘cycle of erosion’ (late 19th century). The term monadnock comes from Mount Monadnock in New Hampshire, USA. NCERT's in-text question asks whether a high landmass can be completely flattened: in theory yes, but in practice uplift, climate change or sea-level change usually interrupt the cycle first.
Exam trapDown-cutting dominates in youth (exercise Q1-i). Meanders mark a mature or old river (UPSC 1990 — ‘maturity of a river course is recognised by meanders’), while gorges and V-valleys mark youth.
2. Erosional landforms of running water
In simple wordsA river is a saw and a drill at the same time. Fast and steep, it saws straight down — gorges and canyons. Carrying pebbles, it drills holes in its rocky bed — potholes. Lifted up later, it saws down into its own old floor — leaving steps called terraces.
| Landform | How it forms (NCERT) |
|---|---|
| Valleys | Rills → gullies → valleys. Types depend on rock type and structure |
| Gorge | Deep valley with very steep to straight sides; about as wide at the top as at the bottom; forms in hard rocks |
| Canyon | Steep step-like side slopes; wider at the top than the bottom; a variant of a gorge; forms in horizontally bedded sedimentary rocks |
| Potholes | Roughly circular hollows in rocky stream beds, drilled by pebbles and boulders swirled by the current; they join and deepen the valley |
| Plunge pools | Large, deep potholes at the foot of waterfalls, from the impact of falling water and rotating boulders |
| Incised / entrenched meanders | Deep, wide meanders cut into hard rock — the meander pattern was set earlier on a gentle surface, then the river cut down as the land rose |
| River terraces | Old valley-floor or floodplain levels left as the river cuts down into its own floodplain; bedrock or alluvial; paired when at the same height on both banks |
Reading NCERT Figures 6.1 and 6.2 — gorge and canyon (page 49)
- Figure 6.1: a black-and-white photo of the Kaveri near Hogenakkal, Dharmapuri district, Tamil Nadu — a narrow slot of water between two near-vertical walls of massive, jointed hard rock (granite-gneiss country). The walls are almost parallel: the top is no wider than the bottom — the textbook gorge.
- Figure 6.2: an aerial photo of an entrenched meander loop of the Colorado (USA). The river swings round a tall rock ‘island’ whose sides fall in steps — layer after layer of flat-lying sedimentary rock — so the valley is much wider at the top: a canyon, and an incised meander at the same time.
Beyond NCERT — Indian examplesGorges: the Indus, Sutlej and Brahmaputra cut deep gorges across the Himalaya (UPSC 2012 listed deep gorges among signs of young fold mountains). Canyons: Gandikota on the Pennar (Andhra Pradesh) is called the ‘Grand Canyon of India’ (UPSC 2022). Waterfalls with plunge pools: Jog (Sharavati), Dhuandhar (Narmada).
3. Depositional landforms of running water
In simple wordsA delivery van that suddenly hits a muddy field drops its heaviest boxes first. A river leaving the mountains does the same at the foot of the slope (an alluvial fan); reaching the still sea it drops everything it has left (a delta); and every flood spreads a thin layer over the plain (the floodplain).
| Alluvial fan | Delta | |
|---|---|---|
| Where | Where a stream from higher ground breaks onto a gentle foot-slope plain | Where a river enters the sea (or a lake) |
| Shape | Broad low-to-high cone; distributaries shift across it | Low cone; distributaries lengthen as it grows seaward |
| Material | Very coarse, poorly sorted | Very well sorted, clearly stratified: coarse settles first, silt and clay carried further out |
| Climate effect | Humid: low cones, gentle slope · arid/semi-arid: high cones, steep slope | Forms only if the load is not carried away or spread along the coast |
Reading NCERT Figures 6.3 and 6.4 (page 50)
- Figure 6.3: a photo on the way to Amarnath, Jammu and Kashmir — a narrow gully cutting a dark mountainside opens onto a pale, smooth cone of debris spreading downhill: a fresh alluvial fan, steep because it is in a dry, high-mountain setting.
- Figure 6.4: a satellite view of part of the Krishna delta, Andhra Pradesh. The dark river channel comes down from the top and, near the coast, splits into several distributaries that fan out into the Bay of Bengal; the delta front bulges into the sea, and old beach ridges show as faint parallel lines on the land.
Floodplains are the major depositional landform of rivers. Coarse material drops first where the channel meets a gentle slope; finer sand, silt and clay are laid on the bed and, during floods, above the banks. The river bed made of river deposits is the active floodplain; the floodplain above the banks is the inactive floodplain, with two kinds of deposit: flood deposits (fine silt and clay from spill-over) and channel deposits (coarse fill of abandoned, cut-off channels). Floodplains in a delta are delta plains.
| Natural levee | Point bar (meander bar) | |
|---|---|---|
| Where | Along the banks of large rivers | On the inner (convex) side of meander bends |
| Shape | Low, linear, parallel ridges, often broken into mounds | Almost uniform in profile and width |
| Material | Coarse deposits dropped when floodwater spills over | Mixed sizes, laid in a linear fashion along the bank |
Reading NCERT Figure 6.5 — Natural levee and point bars (page 50)
- A block diagram of a meandering river on a floodplain (labelled). Raised banks along the channel are labelled natural levee; crescent-shaped ridged deposits on the inside of each bend are labelled point bars.
- The fine curved lines on the point bars are old bar ridges, showing that the bend has migrated outwards step by step.
- The figure places point bars on the inner (convex) side — but the text says they are ‘found on the concave side’. The figure, Figure 6.7 and standard geomorphology all agree: point bars form on the convex (inner) bank. The text's ‘concave’ is a slip.
Meanders. On large flood and delta plains, rivers seldom flow straight; loop-like patterns called meanders develop. NCERT stresses that a meander is not a landform but a channel pattern, caused by (i) water on very gentle gradients working sideways on the banks, (ii) loose, irregular alluvial banks, and (iii) the Coriolis force deflecting the moving water. A slight bend deepens by deposition on the inside and erosion on the outside: deposition on the convex bank (long gentle ‘slip-off’ slope) and undercutting of the concave bank (steep scarp). Deep loops may be cut off at the inflection points, leaving oxbow lakes.
Reading NCERT Figures 6.6 and 6.7 (page 51)
- Figure 6.6: a satellite scene of the Burhi Gandak near Muzaffarpur, Bihar. The river (with a flow arrow) twists in tight loops, and the land around it is scarred with many dark crescent-shaped oxbow lakes and cut-offs — abandoned loops of earlier courses, showing how much the river has wandered.
- Figure 6.7: a sketch of a meandering river with flow arrows, a right bank and left bank, an inflection point (where one bend turns into the next), point bars and slip-off banks (convex) on the inner sides, a cut-off bank (concave) on the outer side, and two oxbow lakes beside the channel.
- The figure's title says ‘undercut banks’ while its labels say ‘cut-off bank’ — the usual term is undercut bank (or cut bank).
Beyond NCERT
- Delta shapes: arcuate (fan-shaped, e.g. Nile), bird's foot (long fingers, e.g. Mississippi), cuspate (tooth-shaped, e.g. Tiber).
- West-flowing Peninsular rivers (Narmada, Tapi) form estuaries, not deltas: short, steep courses through hard rock, little load, and strong tides that sweep sediment away (UPSC 2004; Mains 2013). Conditions that favour deltas: heavy load, a sheltered sea with weak currents and tides.
- Kanwar Taal (Begusarai, Bihar), a Ramsar site, is an oxbow-type wetland formed by the meandering Burhi Gandak (UPSC 2023).
- Many geomorphologists treat the Coriolis force as only a minor influence on meanders compared with bank material and flow dynamics.
Exam trapPoint bar = inner/convex bank (deposition); undercut cliff = outer/concave bank (erosion). Levees are coarse; floodplain spill deposits are fine. Fans are poorly sorted; deltas well sorted.
4. Groundwater and karst landforms
In simple wordsDrop a sugar cube into tea and it vanishes; drip sugary water slowly and it leaves crystals. Limestone behaves like that sugar: rainwater (slightly acidic with CO₂) dissolves it to make holes and caves, and the same water, dripping and evaporating, re-deposits it as stalactites and stalagmites.
Surface water percolates where rocks are permeable, thinly bedded and highly jointed; it goes down, then moves sideways along bedding planes and joints. Mechanical removal by groundwater is insignificant, so its work shows only in rocks rich in calcium carbonate — limestone and dolomite — through solution and precipitation (deposition). Such a landscape is called karst topography, after the Karst region in the Balkans next to the Adriatic Sea.
| Erosional karst form | What it is (NCERT) |
|---|---|
| Swallow hole | Small-to-medium, round to sub-rounded shallow depression on the surface, made by solution |
| Sinkhole | Opening roughly circular at the top and funnel-shaped below; a few sq m to a hectare; under half a metre to 30 m+ deep. Solution sinks (more common) form by solution alone; collapse sinks (‘dolines’) when a cave roof gives way. Soil-covered sinks look like harmless shallow pools |
| Valley sink / uvala | Long, narrow-to-wide trench formed when sinkholes and dolines join (margins slump or cave roofs collapse) |
| Lapies | Maze of sharp points, grooves and ridges from differential solution along parallel joints; may smooth into a limestone pavement |
| Caves | Long narrow-to-wide gaps dissolved along bedding planes, where limestone alternates with other rocks or is dense and thick; caves open at both ends are tunnels |
Reading NCERT Figure 6.8 — Various karst features (page 52)
- Six small sketches: swallow hole in section (a shallow dip in jointed rock), sink hole in section (a deeper funnel narrowing into joints), section of a collapse sink (broken roof blocks piled on a cave floor, with ‘cave’ on both sides), cave in section (labelled stalactite, pillar, cave, stalagmite, cave mouth), and two block diagrams — a surface pitted with many sink holes, and a surface cut into deep elongated trenches labelled valley sinks/uvalas.
- The cave sketch shows that caves follow the bedding planes — the roof and floor are flat rock layers — and that the cave opens at a cave mouth on a hillside, where a cave stream can come out.
Reading NCERT Figure 6.9 — Stalactites and stalagmites (page 53)Two photos from inside limestone caves: (top) a chamber whose roof is hung with icicle-like stalactites and whose floor carries rounded, lumpy stalagmites, with daylight at a cave opening; (bottom) dense curtains of thin stalactites and pale, knobbly columns rising from the floor. Stalactites are broad at the base and taper downward; stalagmites can be columns, discs, rounded knobs or have a small crater-like hollow on top.
Beyond NCERT — karst in IndiaBorra Caves (Araku valley, Andhra Pradesh), Belum Caves (Andhra Pradesh), the long cave systems of Meghalaya (e.g. Krem Liat Prah, one of the longest natural caves in India). A memory hook: stalactites hang from the ceiling, stalagmites rise from the ground.
Exam trapLapies = irregular surface of sharp pinnacles, grooves and ridges (exercise Q1-iv); a sinkhole is the funnel-shaped opening; a swallow hole is the small shallow depression. Collapse sinks are called dolines; joined sinks make uvalas.
5. Glaciers: erosional landforms
In simple wordsA glacier is a slow, heavy bulldozer with rocks frozen into its blade. It scoops out armchair-shaped hollows high on mountains, files peaks into sharp pyramids, and turns narrow V-shaped river valleys into wide U-shaped troughs.
Glaciers are masses of ice moving as sheets over land (continental glaciers, or piedmont glaciers when a vast sheet spreads over the plains at the foot of mountains) or as linear flows down broad trough-like valleys (mountain and valley glaciers). They move slowly — from a few centimetres to a few metres a day — basically because of gravity. Erosion is tremendous because of friction from the sheer weight of ice: plucked angular blocks dragged along floors and sides cause great damage by abrasion and plucking, even to unweathered rock. In time glaciers can reduce high mountains to low hills and vast outwash plains.
Reading NCERT Figure 6.10 and the glacier box (page 54)
- Figure 6.10 ‘A glacier in its valley’: a photo of a broad tongue of white ice filling a valley between dark, snow-streaked mountain slopes, curving away into the distance — showing how ice fills the whole valley width, not just a channel.
- The box: India's glaciers are in the higher reaches of Uttarakhand (printed ‘Uttaranchal’, its old name), Himachal Pradesh and Jammu and Kashmir. The Bhagirathi is fed by meltwater from under the snout of the Gangotri glacier at Gaumukh; the Alkapuri glacier feeds the Alaknanda; the two join at Devprayag to form the Ganga.
- Beyond NCERT: many sources name the Satopanth and Bhagirath Kharak glaciers as the Alaknanda's source (Alkapuri is near their snout).
| Erosional form | What it is (NCERT) |
|---|---|
| Cirque | The most common glacial landform: a deep, long, wide trough or basin with very steep concave to vertical walls at the head and sides, usually at the head of a glacial valley. Often holds a cirque or tarn lake after the ice goes; cirques can step one below another |
| Horn | High, sharp, steep-sided peak where three or more radiating glaciers cut headward until their cirques meet — e.g. Matterhorn (Alps) and Everest (NCERT) |
| Serrated ridge / arête | Divides between cirques narrowed into saw-toothed ridges with very sharp, zig-zag crests |
| Glacial valley / trough | U-shaped, broad floor, relatively smooth steep sides; may hold moraines, swampy debris and lakes gouged in the floor |
| Hanging valley | Tributary valley left high above the main glacial valley; its spur ends are cut into triangular facets (truncated spurs) |
| Fjord / fiord | Very deep glacial trough filled by the sea, forming the shoreline in high latitudes |
Reading NCERT Figure 6.11 — Some glacial erosional and depositional forms (page 55)
- A panoramic sketch (adapted from Spencer, 1962) of glaciated mountains. Labels along the skyline: Col, Horn, Arête; on the slopes: Cirque, Truncated spur, Hanging valley; in the main valley: Lateral moraine, Medial moraine, Terminal moraine; and in front, a braided-stream Outwash plain.
- Col and truncated spur appear only in the figure. A col is a low pass or saddle cut where two cirques eat into a ridge from opposite sides (Beyond NCERT).
- The valley glacier carries dark stripes of debris: those along its edges become lateral moraines, the stripe down its middle (where two glaciers merged) a medial moraine.
Beyond NCERTFamous fjord coasts: Norway, Greenland, southern Chile, New Zealand (Fiordland), British Columbia and Alaska. They are picturesque because of sheer valley walls rising straight out of deep, calm water, hanging valleys with waterfalls, and narrow winding inlets — the theme of Mains 2023.
Exam trapA cirque is the deep basin with steep concave walls (exercise Q1-v); a tarn is the lake in it; a horn is the peak; an arête the ridge. Glacial valleys are U-shaped, river valleys V-shaped.
6. Glaciers: depositional landforms
In simple wordsWhen the ice bulldozer stops and melts, it leaves its load where it stands — a jumble of everything from boulders to dust (till). Meltwater streams then wash some of that load further on and sort it neatly by size (outwash), like a sieve.
| Glacial till | Outwash (glacio-fluvial) deposits | |
|---|---|---|
| Laid by | Melting ice directly | Meltwater streams from the bottom, sides or snout |
| Sorting | Unassorted coarse and fine debris | Roughly stratified and assorted |
| Fragments | Angular to sub-angular | Somewhat rounded edges |
| Landforms | Moraines, drumlins | Eskers, outwash plains |
| Depositional form | What it is (NCERT) |
|---|---|
| Terminal moraine | Long ridge of till at the end (toe) of the glacier |
| Lateral moraine | Ridges along the sides, parallel to the valley; may join the terminal moraine in a horse-shoe; partly pushed up by glacio-fluvial water |
| Medial moraine | In the centre of the valley between lateral moraines; imperfectly formed |
| Ground moraine | Irregular sheet of till left on the floor by rapidly retreating glaciers |
| Esker | Sinuous ridge of coarse material (boulders, blocks) laid by a meltwater stream flowing beneath the ice in an ice-walled channel |
| Outwash plain | Broad flat glacio-fluvial fans at the foot of glacial mountains or beyond ice sheets, joined into plains of gravel, silt, sand and clay |
| Drumlin | Smooth oval ridge of till with some gravel and sand; long axis parallel to ice movement; up to about 1 km long and 30 m high; blunt, steep stoss end faces the glacier, gentle tail points away; formed by debris dumped beneath heavily loaded ice — shows the direction of ice flow |
Reading NCERT Figure 6.12 — Panoramic diagram of glacial landscape (page 56)
- Adapted from Spencer (1962): a broad lowland after the ice has gone. Labels: Outwash plain (twice), Esker (three winding ridges), Drumlin(s) (smooth oval hills in groups), Terminal moraine (a long hummocky ridge across the view) and Outwash with a meltwater stream.
- The eskers snake across the landscape independent of the slope — they were laid inside ice tunnels, not in valleys cut in the ground.
- Small oval water bodies dot the outwash plain (not labelled) — Beyond NCERT, these are kettle lakes, left where buried ice blocks melted.
⤵ How glaciers reduce mountains to plains
Ice accumulates and moves under gravitycm to m per day
Plucking and abrasioncirques, horns, arêtes, U-troughs, hanging valleys
Debris removed, divides loweredslope keeps decreasing
Glacier stops moving and meltstill dropped: moraines, drumlins
Meltwater sorts and spreads debriseskers and vast outwash plains
Low hills and plains remainexercise 3(iii)
Exam trapEskers and drumlins are glacial (UPSC 1990). Eskers are sorted meltwater deposits; drumlins and moraines are till. Till is unsorted; alluvium (river deposit) is sorted and rounded — NCERT's question box.
7. Waves, currents and coastal landforms
In simple wordsWaves are a hammer and a broom. Where the coast is high and rocky, the hammer wins: cliffs are battered, caves hollowed, stacks left standing. Where the coast is low and sandy, the broom wins: sand is swept into beaches, bars and spits that fence off quiet lagoons.
Coastal processes are the most dynamic and hence most destructive; a coast can erode in one season and build up in another. Breaking waves throw water onto the shore and churn the sea-bottom sediment; storm and tsunami waves change coasts far more in a short time. Besides waves, coastal landforms depend on (i) the configuration of land and sea floor and (ii) whether the coast is emerging (advancing seaward) or submerging (retreating landward). Assuming a constant sea level, NCERT compares two types.
| High rocky coast (submerged) | Low sedimentary coast (emerged) | |
|---|---|---|
| Coastline | Highly indented; rivers look drowned; fjords where glacial valleys reach the sea | Smooth, with occasional lagoons and tidal creeks |
| Slope | Hillsides drop sharply into the water | Land slopes gently into the water; marshes and swamps |
| Dominant work | Erosion: cliffs, wave-cut platform; later wave-built terrace, beaches, bars, spits, lagoons | Deposition: bars, barrier bars, spits, lagoons → swamps → coastal plain; deltas from large rivers |
| India | West coast — a high rocky retreating coast | East coast — a low sedimentary coast |
| Erosional form | What it is (NCERT) |
|---|---|
| Sea cliff | Steep face shaped by waves; a few m to 30 m or more |
| Wave-cut platform / terrace | Flat or gently sloping rock platform at the foot of a retreating cliff; called a wave-cut terrace when above average wave height |
| Sea cave | Hollows at the cliff base widened by waves and smashed debris; roofs collapse and the cliff retreats |
| Sea stack | Resistant remnant of a cliff or hill left standing as a small island; temporary — eventually worn away |
| Depositional form | What it is (NCERT) |
|---|---|
| Beach | Temporary deposit of mostly sand (from rivers or wave erosion); can shrink to a strip of pebbles in another season. Shingle beaches have small pebbles and cobbles |
| Coastal dunes | Sand lifted and winnowed from the beach, piled behind it as long ridges parallel to the coast — common on low coasts |
| Offshore bar | Ridge of sand and shingle in the offshore zone, roughly parallel to the coast (submerged) |
| Barrier bar | An offshore bar built up until it shows above water |
| Spit | A barrier bar keyed up to one end of a bay — or attached to a headland |
| Lagoon | A bay closed off by bars and spits; fills with sediment from land and beach (aided by wind) → coastal plain |
Reading NCERT Figure 6.13 and the coastal-defence box (page 59)
- Figure 6.13: a satellite picture of part of the Godavari delta. A long, thin, pale spit curves out from the coast into the dark sea, hooking at its tip, with the delta's cultivated land and channels behind it — sand carried along the coast by longshore currents and attached at one end.
- The box: offshore bars are the first buffer against storms and tsunamis; then come barriers, beaches, beach dunes and mangroves. Anything that disturbs the coastal ‘sediment budget’ or destroys mangroves lets these forms erode and exposes settlements to the first strike — exactly the logic of UPSC GS3 2022 on coastal erosion.
Beyond NCERT — Indian coastsLagoons: Chilika (Odisha; Asia's largest brackish-water lagoon), Pulicat (Andhra Pradesh–Tamil Nadu), the Kerala backwaters (Vembanad, Ashtamudi). An arch forms between a cave and a stack when caves on two sides of a headland meet. Mangroves protect coasts because their dense, spreading roots hold soil and are not uprooted by storms and tides (UPSC 2011). Coastal erosion is driven by dams trapping river sediment, sand mining, ports and breakwaters interrupting longshore drift, and mangrove loss; answers include beach nourishment, shoreline management plans and mangrove restoration.
Exam trapIndia's west coast is high and rocky (erosion dominates); the east coast is low and sedimentary (deposition dominates) — hence the big deltas are on the east. A bar is submerged; a barrier bar shows above water; a spit is attached at one end.
8. Winds and desert landforms
In simple wordsIn a desert, wind is a sand-blaster and a sorting machine: it scours rocks into odd shapes and piles sand into dunes. But the heavy lifting is done by rare, violent rainstorms that send sheets of water across the bare ground.
Wind is one of the two dominant agents in hot deserts. Dry, bare desert floors heat quickly and heat the air above, causing rising hot air, turbulence, eddies, whirlwinds, updrafts and downdrafts; winds also sweep along the floor at high speed. Wind works by deflation (lifting and removing dust and fine particles), abrasion (sand and silt used as tools to grind the surface) and impact (sheer momentum of sand blown against rock, like sand-blasting).
Yet many desert features owe more to mass wasting and running water as sheet floods. Rain is scarce but torrential; bare rocks, weathered fast by drastic daily temperature change, lose their debris to sheet wash. Wind moves the fine material; general mass erosion is mainly by sheet floods. Desert stream channels are broad, smooth, indefinite and flow briefly after rain.
| Erosional form | What it is (NCERT) |
|---|---|
| Pediment | Gently inclined rocky floor at the foot of mountains, with or without a thin debris cover; made by lateral erosion of streams plus sheet flooding |
| Parallel retreat (backwasting) | Once a pediment has a steep wash slope with a cliff (free face) above, both retreat backwards; the pediment grows at the mountain's expense |
| Inselberg | The remnant of the mountain left standing |
| Pediplain | Low, featureless plain that results when high desert relief is reduced |
| Playa | Nearly level plain at the centre of an inland basin, briefly covered by a shallow lake; often salty — then called an alkali flat |
| Deflation hollow | Shallow depression where wind blowing steadily in one direction removes weathered mantle or soil |
| Blowout → cave | Shallow hollows on rock faces from impact and abrasion; some deepen into caves |
| Mushroom, table and pedestal rocks | Resistant rock remnants polished by wind: mushroom (slender stalk, broad cap), table (broad flat top), pedestal |
Wind as a depositor. Wind is a good sorting agent: grains roll, hop (saltation) or ride in suspension by size, and settle as the wind drops according to their critical velocities — so wind deposits are well sorted. With sand and a steady wind, dunes can form anywhere in dry regions; obstacles help start them.
| Dune | Shape | Forms when |
|---|---|---|
| Barchan | Crescent; points (wings) directed downwind | Wind constant and moderate; uniform surface |
| Parabolic | Reversed barchan — wings point upwind | Sand partly covered by vegetation |
| Seif | Like a barchan but with only one wing, which can grow very long and high | Wind conditions shift |
| Longitudinal | Long ridges, low height, parallel to the wind | Poor sand supply, constant wind |
| Transverse | Long, low ridges perpendicular to the wind | Constant wind; sand source is an elongated feature at right angles to the wind |
Reading NCERT Figure 6.14 — Various types of sand dunes (page 60)
- Five panels with open arrows for the wind, which blows from the right in the book's drawing: Barchan (crescents with horns pointing downwind), Seif (crescents with one horn stretched long), Parabolic (U-shapes whose arms point back into the wind), Transverse (wavy ridges standing across the wind) and Longitudinal (long, streamlined ridges lying along the wind).
- The pair barchan–parabolic is the easiest to confuse: same wind, opposite horn directions. Our re-drawing puts the wind on the left; only the relation to the wind matters.
- When sand is plentiful, regular dunes merge and lose their shapes; most desert dunes shift, though a few are stabilised near settlements.
Beyond NCERT — wind and desertificationAeolian (wind) processes drive desertification where land is degraded: overgrazing and ploughing strip the protective cover, deflation blows away fertile topsoil, abrasion damages crops and structures, and moving dunes bury fields, roads and canals (e.g. western Rajasthan, the Indira Gandhi Canal area). Remedies: shelterbelts and windbreaks, sand-dune fixation with grasses and shrubs (e.g. sea buckthorn in cold deserts), rotational grazing — and international action under the UNCCD. This is the frame for Mains 2026 (aeolian processes in desertification and land degradation). The Thar has many barchans; wind-blown dust deposits elsewhere form loess (e.g. northern China).
Exam trapA barchan is a crescent-shaped dune (UPSC 1991) with horns downwind; a parabolic dune's horns point upwind. Mushroom rocks are features of wind erosion. In deserts, sheet floods, not wind, do most of the general erosion.
NCERT's in-text questions — short answers
Model answers to the chapter's grey question boxes.
If a landform is a small-to-medium part of the surface, what is a landscape?
A large tract made up of several related landforms.
Is complete reduction of relief of a high landmass possible?
In theory, yes — long river erosion leads to a peneplain with monadnocks. In practice, uplift, climatic change or sea-level change usually interrupts the cycle before it is complete.
In what way do natural levees differ from point bars?
Levees: along the banks, coarse material dropped by spilling floodwater, linear ridges. Point bars: on the inner (convex) side of bends, mixed sediment deposited by the flowing channel, uniform in width.
What are the basic differences between glacial valleys and river valleys?
Glacial: U-shaped, broad floor, steep smooth sides, hanging valleys, truncated spurs, lakes and moraines on the floor. River: V-shaped, narrow floor, interlocking spurs, no moraines.
Distinguish between river alluvial plains and glacial outwash plains.
Both are fairly flat and sorted, but outwash plains are built by meltwater beyond glaciers, from coarser gravel and sand mixed with silt and clay, often as joined fans; alluvial plains are built by rivers over floodplains, with finer, better-layered silt and clay.
What is the difference between till and alluvium?
Till: unsorted, angular debris dropped by ice. Alluvium: sorted, rounded, layered sediment laid by rivers.
What are the various differences between a high rocky coast and a low sedimentary coast?
See the comparison table in section 7: indented vs smooth outline; steep vs gentle slope; erosion vs deposition dominant; west coast vs east coast of India.
List the erosional features carved out by wind action and by sheet floods.
Wind: deflation hollows, blowouts and caves, mushroom, table and pedestal rocks. Sheet floods (with lateral stream erosion): pediments, inselbergs, pediplains; playas form by deposition in the basins they drain into.
NCERT exercise — answer outlines
The five multiple-choice questions are in the Self-check below. Try each written question yourself first, then open the outline to compare.
2(i) What do incised meanders in rocks and meanders in plains of alluvium indicate? (30 words)
Alluvial meanders: a river on a very gentle gradient working sideways — mature or old stage. Incised meanders in hard rock: the meandering pattern formed earlier on a gentle surface and the river then cut down, indicating uplift (rejuvenation) of the land.
2(ii) Explain the evolution of valley sinks or uvalas. (30 words)
Solution makes swallow holes and sinkholes; collapse of cave roofs makes dolines. As these join — by slumping along their margins or roof collapse — long, narrow-to-wide trenches called valley sinks (uvalas) form.
2(iii) Underground flow of water is more common than surface run-off in limestone areas. Why? (30 words)
Limestone is jointed and soluble; water widens joints and bedding planes by solution, so surface water disappears down swallow holes and sinkholes and flows as underground streams, re-emerging through cave openings.
2(iv) Glacial valleys show up many linear depositional forms. Give their locations and names. (30 words)
Lateral moraines along the valley sides; medial moraine down the centre; terminal moraine across the toe (horse-shoe with laterals); eskers as sinuous ridges along former sub-glacial streams; drumlins aligned with ice flow.
2(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features? (30 words)
By deflation, abrasion and impact, and by sorting and depositing sand into dunes. No: sheet floods, rain wash and mass wasting do most general erosion — pediments, pediplains and playas are largely their work.
3(i) Running water is by far the most dominating geomorphic agent in shaping the earth's surface in humid as well as in arid climates. Explain. (150 words)
Humid regions: abundant rain → overland flow and rivers everywhere; rills → gullies → valleys; erosional forms (gorges, canyons, potholes, incised meanders, terraces) and depositional forms (fans, deltas, floodplains, levees, point bars, oxbows); landscapes evolve from youth to old age and a peneplain.
Arid regions: rain is scarce but torrential; bare rock weathered by temperature change is stripped by sheet floods and sheet wash; lateral stream erosion and sheet flooding make pediments, mountain fronts retreat by backwasting leaving inselbergs and pediplains; inland drainage builds playas. Wind moves only fine material.
Comparison: glaciers, waves and groundwater act only in special settings; running water acts almost everywhere.
Conclude: hence running water is the dominant agent in both climates.
Arid regions: rain is scarce but torrential; bare rock weathered by temperature change is stripped by sheet floods and sheet wash; lateral stream erosion and sheet flooding make pediments, mountain fronts retreat by backwasting leaving inselbergs and pediplains; inland drainage builds playas. Wind moves only fine material.
Comparison: glaciers, waves and groundwater act only in special settings; running water acts almost everywhere.
Conclude: hence running water is the dominant agent in both climates.
3(ii) Limestones behave differently in humid and arid climates. Why? What is the dominant process in limestone areas and its results? (150 words)
Why different: limestone (CaCO₃) dissolves in carbonated rainwater. In humid climates plentiful water and CO₂ (from air and decaying vegetation) make solution intense → karst. In arid climates there is little water, so solution is weak; limestone behaves as a resistant rock, often forming cliffs and ridges.
Dominant process: solution (with re-deposition by precipitation).
Results — erosional: swallow holes, sinkholes (solution and collapse/dolines), uvalas, lapies and limestone pavements, caves and tunnels; surface streams vanish underground.
Depositional: stalactites, stalagmites, pillars/columns.
Examples (Beyond NCERT): the Karst region (Balkans); Borra caves, Meghalaya caves in India.
Dominant process: solution (with re-deposition by precipitation).
Results — erosional: swallow holes, sinkholes (solution and collapse/dolines), uvalas, lapies and limestone pavements, caves and tunnels; surface streams vanish underground.
Depositional: stalactites, stalagmites, pillars/columns.
Examples (Beyond NCERT): the Karst region (Balkans); Borra caves, Meghalaya caves in India.
3(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains? (150 words)
Movement: ice moves under gravity, slowly, but its weight gives tremendous friction.
Erosion: plucking and abrasion by embedded angular blocks; cirques bite into mountain tops; headward erosion makes horns and arêtes; valleys widened into U-troughs; tributaries left hanging; spurs truncated.
Removal: eroded debris carried away; divides lowered; slopes reduced.
End stage: when slopes become too gentle the glacier stops and melts, dropping till as moraines and drumlins, while meltwater spreads sorted debris as eskers and vast outwash plains.
Result: only low hills and plains remain.
Diagram: sketch of cirque–horn–arête–U-valley with moraines and outwash.
Erosion: plucking and abrasion by embedded angular blocks; cirques bite into mountain tops; headward erosion makes horns and arêtes; valleys widened into U-troughs; tributaries left hanging; spurs truncated.
Removal: eroded debris carried away; divides lowered; slopes reduced.
End stage: when slopes become too gentle the glacier stops and melts, dropping till as moraines and drumlins, while meltwater spreads sorted debris as eskers and vast outwash plains.
Result: only low hills and plains remain.
Diagram: sketch of cirque–horn–arête–U-valley with moraines and outwash.
Project work: identify landforms, materials and processes around your area
List the landforms near you (river valley, floodplain, terrace, hill, beach, dune, etc.), note the material (rock, sand, silt, clay, gravel), identify the agent at work (running water, waves, wind, ice, groundwater) and the process (erosion or deposition), and sketch one cross-section.
What to remember
Numbers
Stages of landform evolution3 — youth, mature, old
Sinkhole sizea few sq m to a hectare
Sinkhole depth< 0.5 m to 30 m or more
Glacier speeda few cm to a few m a day
Drumlin sizeup to ~1 km long, ~30 m high
Sea cliff heighta few m to 30 m or more
Radiating glaciers needed for a horn3 or more
Types of moraine4 — terminal, lateral, medial, ground
Dune types in Figure 6.145
Ways wind erodes3 — deflation, abrasion, impact
Causes of meandering (NCERT)3 — gentle gradient, loose banks, Coriolis force
Bhagirathi + Alaknanda meet atDevprayag → Ganga
Bhagirathi source (snout)Gaumukh, Gangotri glacier
Spencer's glacial diagrams1962
One-liners
- Steep gradient → down-cutting; gentle gradient → lateral erosion and deposition.
- Gorge: hard rock, top ≈ bottom width. Canyon: horizontal sedimentary beds, stepped, wider at top.
- Alluvial fans are poorly sorted; deltas are well sorted and stratified.
- A meander is a channel pattern, not a landform.
- Groundwater's mechanical work is insignificant — karst needs limestone or dolomite.
- Collapse sinks = dolines; joined sinks = uvalas.
- Till is unsorted; outwash is sorted and layered.
- Drumlin's stoss end faces the ice; it shows the direction of ice movement.
- Bar submerged; barrier bar exposed; spit attached at one end; lagoon enclosed.
- Barchan horns downwind; parabolic horns upwind; seif has one wing.
- Pediments retreat by backwasting, leaving inselbergs and pediplains.
Traps to avoid
- Point bars form on the convex (inner) bank — NCERT's text says ‘concave’, its figures show convex.
- Meanders indicate maturity; gorges and V-valleys indicate youth.
- Eskers and drumlins are glacial, not wind or river features.
- A cirque is the basin; a tarn the lake in it; a horn the peak.
- Lapies = ridges and pinnacles; a swallow hole is a shallow pit; a sinkhole a funnel.
- Stalactites hang from the ceiling; stalagmites rise from the ground.
- West coast of India: high, rocky, erosional. East coast: low, sedimentary, depositional.
- Desert erosion is mostly by sheet floods, not wind.
- West-flowing Peninsular rivers make estuaries, not deltas.
- Parabolic dunes are reversed barchans (same wind, horns upwind).
How to strategise
Prelims — what UPSC asks
- Identification questions dominate: eskers and drumlins are glacial (1990); a barkhan is a crescent-shaped dune (1991); meanders mark river maturity (1990). Make a three-column sheet: landform · agent · erosional or depositional.
- Deltas and estuaries: what does not favour delta formation — strong currents and tides (1983); west-flowing Peninsular rivers have no deltas, but not because they lack sediment (2004).
- Indian applications: meandering of the (Burhi) Gandak and Kanwar lake (2023) — exactly NCERT's Figure 6.6 river; mangroves as a tsunami safety hedge (2011) — the coastal-defence box.
- Read the figures: Figure 6.11's col and truncated spur, Figure 6.14's dune–wind relations and Figure 6.7's convex/concave banks are typical statement material.
Mains — where it appears and how to answer
- GS1 (Geography): why Western Ghats rivers form no deltas (2013); how fjords form and why they are picturesque (2023); the role of aeolian processes in desertification and land degradation (2026).
- GS3 (Disaster management): causes and effects of coastal erosion in India and management techniques (2022) — build on the sediment-budget box: bars, beaches, dunes and mangroves as natural defences; dams, sand mining, ports and mangrove loss as causes.
- Answer frame: agent → process (erosion/deposition) → landform with a labelled sketch → Indian example → human use or hazard. One clean sketch (meander and oxbow, glacial valley, spit and lagoon, dune types) is worth many lines.
- Comparisons are a staple: V vs U valley, fan vs delta, till vs outwash, levee vs point bar, rocky vs sedimentary coast, barchan vs parabolic.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. In which of the following stages of landform development is downward cutting dominated?
2. A deep valley characterised by steep step-like side slopes is known as
3. In which one of the following regions is the chemical weathering process more dominant than the mechanical process?
4. Which one of the following sentences best defines the term ‘Lapies’?
5. A deep, long and wide trough or basin with very steep concave high walls at its head as well as in sides is known as:
6. Point bars are deposited on the…
7. The horns of a parabolic dune point…
8. Which of these is formed mainly by glacial meltwater rather than directly by ice?
UPSC questions from this chapter
Open any question to attempt it in the Question bank — your attempt is saved to your progress.