Landforms and their Evolution – Class 11 Geography Chapter 6 Notes & NCERT PDF

Class 11GeographyChapter 6NCERT book: Fundamentals of Physical Geography - Geography Class 11

Notes and a simple summary of Chapter 6 of the NCERT Class 11 Geography book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 6: Landforms and their Evolution

Introduction

After weathering, geomorphic agents — running water, groundwater, glaciers, waves and wind — erode, transport and deposit material, creating landforms. A landform is a small-to-medium tract of the earth's surface; several related landforms make a landscape. Every landform has a beginning and a history of change. A landmass passes through stages like life — youth, mature and old age. This chapter describes the erosional and depositional landforms made by each agent.

Key Concepts

Running water

Most important agent in humid regions. Two components: overland flow (sheet erosion) and linear flow (streams and rivers). Sheet flow concentrates into rills → gullies → valleys. The end product is a nearly flat peneplain with resistant remnants called monadnocks.

Stages of landscape development

Youth: few, poorly integrated streams; shallow V-shaped valleys; no or narrow floodplains; waterfalls and rapids over hard rock.

Mature: many well-integrated streams; deep V-shaped valleys; wider floodplains with meanders; waterfalls disappear.

Old: few small tributaries with gentle gradients; streams meander freely over vast floodplains with natural levees and oxbow lakes; landscape at or slightly above sea level.

Erosional landforms

Valleys: V-shaped, gorge and canyon. A gorge has very steep, straight sides, almost equal in width at top and bottom (forms in hard rocks). A canyon has steep step-like sides, wider at the top (forms in horizontally bedded sedimentary rocks); a canyon is a variant of a gorge. Example: gorge of the Kaveri near Hogenekal; entrenched meander of the Colorado (USA).

Potholes: circular depressions on rocky beds formed by abrasion with rotating pebbles. Plunge pools: large, deep holes at the base of waterfalls.

Incised or entrenched meanders: very deep, wide meanders cut in hard rock.

River terraces: surfaces marking old valley floor or floodplain levels; products of erosion as the stream cuts into its own floodplain; paired terraces occur at the same height on both sides.

Depositional landforms

Alluvial fans: cone-shaped deposits where streams from higher levels break onto low-gradient foot slopes; streams split into distributaries. Low gentle cones in humid areas; high steep cones in arid areas.

Deltas: like fans but at the river mouth in the sea; deposits well sorted and stratified. Example: Krishna delta.

Floodplains: major depositional landform; active floodplain (river bed) and inactive floodplain (above banks) with channel deposits (coarse) and flood deposits (fine silt and clay). Floodplains in a delta are delta plains.

Natural levees: low, linear ridges of coarse deposits along the banks of large rivers.

Point bars (meander bars): linear sediment deposits along the bank on the inside of meanders, with mixed sizes.

Meanders: loop-like channel pattern — not a landform, only a channel pattern — caused by gentle gradients, unconsolidated banks and Coriolis force. Deposition occurs on the convex (slip-off) bank and undercutting on the concave (cut-off) bank. Loops cut off at inflection points leave oxbow lakes (e.g. Burhi Gandak near Muzaffarpur).

Groundwater (karst topography)

Groundwater's work is significant only in rocks like limestone and dolomite (calcium carbonate), through solution and precipitation. Such topography is called karst, after the Karst region in the Balkans near the Adriatic Sea.

Sinkholes: circular openings, funnel-shaped towards the bottom; a few sq. m to a hectare, less than half a metre to thirty metres or more deep. Solution sinks (more common) and collapse sinks (dolines).

Valley sinks / uvalas: long trenches formed when sinkholes and dolines join.

Lapies: irregular surface of points, grooves and ridges from differential solution along joints; may turn into limestone pavements.

Caves: form along bedding planes in thick limestone; caves open at both ends are tunnels.

Depositional forms in caves: stalactites hang like icicles; stalagmites rise from the floor; they fuse into columns and pillars.

Glaciers

Masses of ice moving as sheets (continental or piedmont glaciers) or as linear flows in valleys (mountain/valley glaciers), mainly under gravity, a few centimetres to metres a day. The Bhagirathi is fed by meltwater from the snout (Gaumukh) of the Gangotri glacier; the Alkapuri glacier feeds the Alaknanda; they join at Deoprayag to form the Ganga. Glaciers erode by abrasion and plucking.

Erosional landforms

Cirque: deep, long, wide trough or basin with very steep concave walls at the head of glacial valleys; may hold a cirque/tarn lake.

Horns: sharp peaks formed by headward erosion of three or more radiating cirques — Matterhorn (Alps) and Everest are horns. Arêtes: serrated, saw-toothed ridges between cirques.

Glacial valleys/troughs: U-shaped with broad floors; hanging valleys and triangular facets; deep troughs filled with sea water are fjords.

Depositional landforms

Till (unassorted, angular) vs outwash (stratified, assorted, rounded).

Moraines: ridges of till — terminal (at the toe), lateral (along the sides), ground (irregular sheet on the floor), medial (centre of the valley).

Eskers: sinuous ridges of coarse material left by streams flowing beneath glaciers.

Outwash plains: broad plains of glacio-fluvial deposits beyond the ice.

Drumlins: smooth oval ridges of till, up to 1 km long and 30 m high; blunt stoss end faces the glacier; they indicate the direction of ice movement.

Waves and currents

Coastal processes are the most dynamic and destructive. Two coast types (assuming constant sea level):

High rocky coasts (submerged): drowned, highly indented coastline; erosion dominates; cliffs, wave-cut platforms. India's west coast is high, rocky and retreating.

Low sedimentary coasts (emerged): smooth coastline with lagoons and tidal creeks; deposition dominates. India's east coast is low and sedimentary.

Erosional landforms: wave-cut cliffs and terraces, sea caves, and sea stacks (isolated rock remnants).

Depositional landforms: beaches (temporary; sand or shingle), coastal dunes, off-shore bars, barrier bars, spits (bars keyed to a headland or one end of a bay; e.g. Godavari delta), and lagoons that fill up to form coastal plains.

Winds (deserts)

In hot deserts, wind causes deflation, abrasion and impact; much desert erosion is also done by sheet floods after torrential rain.

Pediments: gently inclined rocky floors at the foot of mountains, extended by parallel retreat of slopes (backwasting); the mountain reduces to an inselberg, and finally a pediplain forms.

Playas: shallow temporary lakes in basin centres; salt-covered playas are alkali flats.

Deflation hollows, blow-outs and caves.

Mushroom rocks: resistant remnants shaped by abrasion.

Sand dunes (wind is a good sorting agent):

Barchans: crescent-shaped, points directed downwind; constant moderate wind and uniform surface.

Parabolic dunes: reversed barchans where sand is partly covered by vegetation.

Seif: like a barchan with only one wing, due to a shift in wind conditions.

Longitudinal dunes: long, low ridges when sand supply is poor and wind direction constant.

Transverse dunes: perpendicular to wind direction; sand source elongated at right angles to the wind.

Diagrams to Know

Figure 6.7 — meander growth, cut-off loops, slip-off and undercut banks.

Figure 6.8 — karst features: sinkholes, uvalas, lapies, caves.

Figures 6.11–6.12 — glacial forms: cirque, horn, arête, U-valley, moraines, esker, drumlin, outwash plain.

Figure 6.14 — types of sand dunes with wind arrows.

Key-Facts Sheet

Youth = down-cutting; old age = free meanders over floodplains

Canyon: step-like, wider at top; gorge: straight sides, equal width

Karst = limestone/dolomite, solution and precipitation

Everest and Matterhorn = horns

West coast of India = high rocky; east coast = low sedimentary

Exam Focus

MCQs: down-cutting dominates in the youth stage; step-like valley = canyon; chemical weathering dominant in humid/limestone regions; lapies = irregular surface with pinnacles, grooves and ridges; cirque definition.

30-word answers: incised meanders vs meanders in alluvium; evolution of uvalas; why underground flow dominates in limestone; linear glacial deposits (moraines, eskers, drumlins); how wind works in deserts and the role of sheet floods.

150-word answers: dominance of running water in humid and arid climates; how glaciers reduce mountains to low hills and plains.

Key Terms

Landform (भू-आकृति)

Peneplain (समप्राय मैदान)

Gorge (महाखड्ड)

Canyon (कैनियन)

Alluvial fan (जलोढ़ पंख)

Delta (डेल्टा)

Oxbow lake (गोखुर झील)

Sinkhole (घोलरंध्र)

Stalactite (स्टैलेक्टाइट / आश्चुताश्म)

Cirque (सर्क)

Moraine (हिमोढ़)

Sand dune (बालू का टिब्बा)

Common Mistakes

Calling a meander a landform — the book says it is only a channel pattern.

Mixing up stalactites (hang from the roof) and stalagmites (rise from the floor).

Saying barchan points face the wind — they point downwind.

Confusing till (unassorted, angular) with outwash (assorted, stratified, rounded).

Note: the text places point bars on the concave side in one line but also says deposition is on the convex bank; for meanders, remember deposition on the convex (inner) bank and undercutting on the concave (outer) bank.

💡 Key Learning Points

✓Landscapes evolve through youth, mature and old stages; running water forms valleys, gorges, canyons, potholes, terraces, fans, deltas, floodplains, levees and meanders.
✓Groundwater creates karst topography in limestone — sinkholes, uvalas, lapies, caves, stalactites, stalagmites and pillars.
✓Glaciers erode cirques, horns, arêtes and U-shaped valleys, and deposit till, moraines, eskers, outwash plains and drumlins.
✓Waves shape high rocky coasts (cliffs, sea caves, stacks) and low sedimentary coasts (beaches, bars, spits, lagoons); India's west coast is rocky and east coast sedimentary.
✓Wind and sheet floods in deserts form pediments, pediplains, playas, mushroom rocks and different types of sand dunes.

👨‍🏫 Teaching Tips

→Use a sand tray with a hose to model valleys, alluvial fans and deltas.
→Show satellite images from the book (Krishna delta, Burhi Gandak meanders, Godavari spit) and let students identify features.
→Put chalk in carbonated water to model limestone solution in karst areas.
→Build a 'landform bank' chart classifying each landform by agent and erosional/depositional type.
→Use ice cubes containing sand dragged over clay to demonstrate glacial abrasion and till deposition.
→Draw the five dune types with wind arrows and quiz students on wind direction.
→Assign the Project Work: identify landforms, materials and processes in the local area.

📋 Assessment Questions

Can the student describe the stages of youth, maturity and old age in a running-water landscape?
Can the student distinguish gorge and canyon, till and outwash, stalactite and stalagmite?
Can the student explain the formation of uvalas, horns, oxbow lakes and pediplains?
Can the student compare high rocky coasts and low sedimentary coasts with Indian examples?
Can the student identify the type of sand dune from wind and sand conditions?

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