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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 chaptersGeomorphic Processes
Start here: why this chapter matters
In simple wordsPicture a sandcastle on a beach. Someone keeps piling sand up (forces from inside the earth); the waves and wind keep knocking it down and spreading it out (forces from outside). The shape you see at any moment is the result of that contest. This chapter is about the outside forces — how rock is broken, moved and turned into soil.
Unit II explained the inside story: plates, earthquakes and volcanoes that build relief. Unit III (this chapter and the next) explains how that relief is worn down and reshaped. Chapter 5 gives the processes — weathering, mass movement, erosion, deposition and soil formation; Chapter 6 shows the landforms each agent makes.
- Opens Unit III, ‘Landforms’; leads straight into Chapter 6 (Landforms and their Evolution).
- Links back to Chapters 3–4 (endogenic forces) and to soils in Class 11 India: Physical Environment.
- UPSC: Mains GS1 asked about landslides in the Himalayas vs the Western Ghats three times (2013, 2016, 2021) — straight from this chapter's box; GS3 disaster management asked landslide hazard zonation (2019) and risk management (2021). Prelims tests weathering and soil processes.
| Word | What it means here |
|---|---|
| Endogenic / exogenic | Forces from inside the earth / from outside (atmosphere, driven by the sun) |
| Degradation / aggradation | Wearing down of high ground / filling up of low ground |
| Gradation | Wearing down of relief by erosion (NCERT's definition) |
| Denudation | All the exogenic processes together (‘denude’ = strip off, uncover) |
| Weathering | Breaking and rotting of rock where it lies, by weather and climate |
| In situ | On the spot, without being carried away |
| Mass movement / mass wasting | Rock and soil moving downslope under gravity alone |
| Geomorphic agent | A moving medium — running water, ice, wind, waves — that picks up, carries and drops material |
| Regolith | The layer of loose, weathered material over solid rock |
| Pedogenesis | Soil formation |
| Humus | Finely divided, decomposed organic matter in soil |
At a glance — the six ideas to carry away
- Endogenic forces (from inside) build land up; exogenic forces (sun-driven) wear it down — relief lasts while both act.
- Diastrophism: orogeny (folding, narrow belts), epeirogeny (broad uplift), earthquakes, plate tectonics.
- Denudation = weathering + mass movements + erosion/transportation; each has its own driving force (Figure 5.1).
- Weathering is in situ: chemical, physical, biological. It prepares soil and enriches ores — but is not essential for erosion.
- Mass movements are gravity alone — no agent — so they are not erosion. Landslides are rapid and fairly dry.
- Soil = five factors: parent material, topography (passive), climate (active), biological activity, time.
1. Why the surface is uneven: two opposing forces
In simple wordsA potter keeps adding clay to a pot while a sculptor keeps scraping it away. As long as both keep working, the pot never becomes smooth. The earth's surface is the same: inside forces keep adding relief, outside forces keep scraping it off.
The crust is dynamic: it has moved, and still moves, vertically and horizontally (a little faster in the past than now). Internal (endogenic) forces built the crust unevenly. External (exogenic) forces, powered by sunlight and acting from the atmosphere, then work on it. Exogenic action causes degradation (wearing down of high ground) and aggradation (filling of basins and depressions). Wearing down of relief through erosion is called gradation. Because endogenic forces keep raising parts of the surface, exogenic processes never manage to make it flat — relief lasts as long as the two keep opposing each other.
| Endogenic | Exogenic | |
|---|---|---|
| Source of energy | Inside the earth: radioactivity, rotational and tidal friction, primordial heat | The sun (via the atmosphere) + slopes made by tectonics |
| Main effect | Land building — raise and build up the crust | Land wearing — wear down and fill up |
| Processes | Diastrophism, volcanism | Weathering, mass wasting, erosion, deposition |
Processes and agents. A geomorphic process is any endogenic or exogenic force that causes physical stress or chemical action on earth materials and changes the surface. A geomorphic agent is a mobile medium — running water, groundwater, glaciers, wind, waves and currents — which removes, transports and deposits material; agents move because of gradients. NCERT notes that, for exogenic forces, ‘process’ and ‘agent’ are usually used for the same thing.
Gravity: the switch for everythingGravity pulls every loose particle downslope and stresses earth materials; indirectly it drives wave and tide currents and winds. Without gravity and gradients there would be no movement — and so no erosion, transportation or deposition. All movement, inside or on the earth, goes down a gradient: from high to low level, from high to low pressure.
Beyond NCERTThe book says most of the surface was shaped over ‘hundreds and thousands of years’. Geomorphologists usually work on much longer spans — thousands to millions of years — for large landforms; short-term change (a landslide, a flood) can still be sudden. The chapter's opening also refers to ‘rocks and minerals’ and ‘igneous rocks in the preceding chapter’: that chapter has been dropped from the current book.
Exam trapEndogenic = land-building; exogenic = land-wearing. Volcanism and diastrophism are endogenic geomorphic processes, not exogenic ones.
2. Endogenic processes: diastrophism and volcanism
In simple wordsPush a tablecloth from both ends and it rucks up into tight folds in one strip — that is orogeny, mountain building. Lift the whole table a little at one corner — the cloth tilts gently over a large area — that is epeirogeny, continent building.
Energy from within — radioactivity, rotational and tidal friction, and primordial heat — flows outwards along geothermal gradients and drives diastrophism and volcanism. Because heat flow, crustal thickness and strength vary from place to place, endogenic action is uneven, and so the original crustal surface is uneven.
| Diastrophism includes… | What it does |
|---|---|
| (i) Orogenic processes | Mountain building by severe folding in long, narrow belts |
| (ii) Epeirogenic processes | Uplift or warping of large parts of the crust — simple deformation |
| (iii) Earthquakes | Local, relatively minor movements |
| (iv) Plate tectonics | Horizontal movements of crustal plates |
⤵ From inner heat to new rocks and landforms
Energy inside the earthradioactivity · rotational and tidal friction · primordial heat
Geothermal gradient and heat flowuneven from place to place
Diastrophismorogeny · epeirogeny · earthquakes · plate tectonics
Folding, faulting, fracturingpressure, volume and temperature (PVT) changes
Metamorphism of rocksrocks altered by PVT
Volcanismmagma moves onto or towards the surface
Intrusive and extrusive formscovered in Chapter 3
An uneven original surfaceon which exogenic processes then work
Exam trapOrogeny = mountain building (severe folding, narrow belts); epeirogeny = continent building (broad uplift or warping, simple deformation). And volcanism is the whole process of magma moving up and forming landforms, while a volcano is one vent or structure.
3. Exogenic processes and denudation
In simple wordsA wooden bench left outside for years cracks in the sun, rots in the rain, and its splinters are blown or washed away. No single event is dramatic, but the bench is slowly ‘denuded’. Rocks suffer the same slow wear — the sun is the ultimate power source.
Exogenic processes draw energy from the atmosphere, driven ultimately by the sun, and from slopes created by tectonic forces. Gravity acts on any sloping surface. Stress is force per unit area, produced by pushing or pulling; forces along the faces of materials are shear stresses — these break rocks and cause slippage. Rocks also suffer molecular stresses from temperature change, crystallisation and melting, while chemical processes loosen grains and dissolve soluble minerals or cements. The basic reason for weathering, mass movement and erosion is stress building up inside earth materials.
All exogenic processes together are called denudation — weathering, mass wasting/movements, erosion and transportation.
Reading NCERT Figure 5.1 — Denudational processes and their driving forces (page 39)
- A simple two-row chart. The top row (Process) has three boxes under ‘Denudational processes’: Weathering, Mass movements, Erosion/Transportation.
- The bottom row (Driving force/energy) pairs each with its force: weathering ← gravitational/molecular stresses and/or chemical actions; mass movements ← gravitational force; erosion/transportation ← kinetic energy.
- The point the text draws: each process has its own distinct driving force. Deposition is not in the chart — it happens when the kinetic energy runs out.
- Note: later the text says ‘as indicated in Figure 6.1’ — it means this Figure 5.1.
| What makes exogenic processes vary | How |
|---|---|
| Climate (temperature and precipitation are the two key elements) | Climatic regions differ by latitude, season and land–water distribution, so processes differ from region to region; vegetation (which depends on rain and temperature) also matters |
| Local differences within a climate | Altitude; aspect (north- vs south-facing slopes get different sunshine); wind speed and direction; amount, kind and intensity of precipitation; precipitation vs evaporation; daily temperature range; freeze–thaw frequency; frost depth |
| Rock type and structure | Folds, faults, dip of beds, joints, bedding planes, hardness of minerals, chemical susceptibility, permeability. A rock may resist one process but not another, so processes work at different rates and create differences in topography |
NCERT's question: the sole driving force?The sun. Solar energy creates temperature differences, winds, evaporation and rain; these drive weathering, running water, glaciers and waves. Gravity acts on the slopes, but the sun supplies the energy that sets the agents moving (exercise 3-ii).
4. Weathering
In simple wordsLeave an iron nail and a biscuit outside for a month. The nail rusts (a chemical change), the biscuit cracks and crumbles (a physical change), and ants carry bits away (a living change). Rocks weather in exactly these three ways — only far more slowly, and in place.
Weathering is the mechanical disintegration and chemical decomposition of rocks by the elements of weather and climate. Since little or no motion takes place, it is an in-situ (on-site) process. Its type and the depth of the weathering mantle depend on geology, climate, topography and vegetation — climate above all.
Reading NCERT Figure 5.2 — Climatic regimes and depth of weathering mantles (page 40)
- Read from left (high latitude, cold) to right (equator, hot and wet). Zones across the top: Tundra · Taiga–Podsol · Steppe · Semi-desert and Desert · Savanna · Tropical Forest (> 3,000 mm). The book's activity asks you to mark their latitudes.
- Two curves: temperature rises steadily towards the equator (to about 25°C); precipitation peaks modestly in the taiga (~600 mm), sinks in the steppe and desert, then shoots up in the savanna and tropical forest to about 3,000 mm.
- Below ground, the weathering mantle: very thin in tundra; moderate in the taiga; very thin in steppe and desert; deepest by far under tropical forest.
- Its legend has six zones: (1) fresh rock, (2) little chemical alteration, (3) moderate to good chemical alteration, (4) clay mineral zone, (5) zone dominated by oxides of aluminium, (6) soil with oxides of iron and aluminium. Zones 4–6 are thick only in the humid tropics — the setting of laterite and bauxite.
- Lesson: heat + water = deep chemical weathering; cold or dry = shallow, mostly mechanical weathering. Source: adapted from Strakhov, 1967.
- The activity box calls it ‘Figure 6.2’ — it means this Figure 5.2.
| Group | What happens (NCERT) | Needs / caused by |
|---|---|---|
| Chemical | Solution, carbonation, hydration, oxidation and reduction decompose, dissolve or reduce rock to a fine state through reactions with oxygen, surface/soil water and acids | Water and air (O₂, CO₂) plus heat; decaying plants and animals add CO₂ underground |
| Physical (mechanical) | Forces fracture rock: gravity (overburden pressure, load, shearing stress); expansion (temperature change, crystal growth, animal activity); water pressure in wetting and drying | Mostly thermal expansion and pressure release; small, slow, but repeated → fatigue |
| Biological | Organisms add or remove minerals and ions and physically break rock: burrowing earthworms, termites, rodents; ploughing humans; roots pressing apart rock; decaying matter making humic and carbonic acids | Living things |
Beyond NCERT — the individual processes (from the earlier edition of this book)
- Solution: soluble minerals (nitrates, sulphates, potassium salts) dissolve in water.
- Carbonation: CO₂ + water → weak carbonic acid, which turns calcium carbonate (limestone) into soluble calcium bicarbonate — how caves form. It works better in cold water, which holds more CO₂ — the ‘exception’ NCERT mentions under temperature.
- Hydration: chemical addition of water. Minerals swell — e.g. calcium sulphate becomes gypsum; clay minerals swell and shrink with wetting and drying.
- Oxidation: iron minerals combine with oxygen → red/brown rust colours (well-aired places). Reduction: in waterlogged, airless places iron turns to the ferrous form → grey-green or bluish colours.
- Physical: unloading (removal of overlying rock lets the rock expand and crack in sheets), temperature changes (outer layers expand and contract more than the inside), freeze–thaw (water expands about 9% on freezing and wedges cracks open — frost wedging), salt weathering (salt crystals grow in pores, common in deserts).
Reading NCERT Figure 5.3 — Exfoliation (Flacking) and granular disintegration (page 41)
- A close-up photo of bare rock with rounded, onion-like humps whose surface layers are peeling off in thin curved sheets (exfoliation), and patches where the surface has crumbled into loose grains (granular disintegration). A small object rests on the rock for scale.
- NCERT stresses that exfoliation is a result, not a process: the processes behind it are unloading, thermal expansion and contraction, and salt weathering. Exfoliation domes come from unloading; tors from thermal expansion.
- The caption's ‘Flacking’ is a misprint for flaking. The text says these processes were ‘already explained under physical weathering’, but that detail is not in the current reprint — see the Beyond NCERT box above.
Why weathering matters: it breaks rock into fragments and prepares the way for regolith and soils, erosion and mass movements. Biomes and biodiversity rest on forests, and forests depend on the depth of the weathering mantle. Erosion cannot be significant if rocks are not weathered. Weathering also causes enrichment: leaching by groundwater removes some materials, so the remaining valuable ones — ores of iron, manganese, aluminium, copper — become concentrated enough to mine profitably.
Exam trapWeathering is in situ — the little movement it causes is not transportation, because no agent carries the material away. Weathering aids erosion and mass movement but is not a pre-condition for either.
5. Mass movements and landslides
In simple wordsPile wet sand on a slope and it eventually slumps on its own — nothing carries it, it just falls. That is mass movement: gravity alone. If a stream had washed the sand away, that would be erosion.
Mass movements transfer rock debris down slopes under the direct influence of gravity. Air, water or ice do not carry the debris; rather the debris may carry air, water or ice with it. Movements range from slow to rapid and shallow to deep, and include creep, flow, slide and fall. Because no geomorphic agent takes part, mass movements are not erosion, even though material shifts. Weathering is not a pre-requisite, but mass movements are much more active on weathered slopes. Material yields only when the disturbing force exceeds its shearing resistance.
| Conditions that favour mass movement | Activating causes (NCERT's nine) |
|---|---|
| Weak, unconsolidated materials; thinly bedded rocks; faults; steeply dipping beds; vertical cliffs and steep slopes; abundant and torrential rain; scarce vegetation | (i) removal of support from below · (ii) steeper and higher slopes · (iii) overloading by added material · (iv) overloading by heavy rain, saturation and lubrication · (v) removal of load from the original slope · (vi) earthquakes, explosions, machinery · (vii) excessive natural seepage · (viii) heavy drawdown of lakes, reservoirs, rivers · (ix) removal of natural vegetation |
The three forms of movement are heave (soil pushed up by frost growth and other causes), flow and slide. Landslides are relatively rapid and perceptible, and the material is relatively dry. Their size and shape depend on discontinuities in the rock, the degree of weathering and the steepness of the slope.
Reading NCERT Figure 5.4 — Slumping of debris with backward rotation (page 42)
- A cross-section of a slope cut into horizontal rock layers. A dotted line marks the initial position of the slope.
- The slump body has slid down a curved (spoon-shaped) surface; its internal layers are tilted back towards the hill — labelled ‘slump body showing backward rotation of materials’.
- At the top a steep scarp is left where the block broke away; at the toe the material bulges out over the flat ground.
| Landslide type | Movement | Key point |
|---|---|---|
| Slump | One or several units of debris slip with backward rotation | Curved slip surface |
| Debris slide | Rapid rolling or sliding of earth debris | No backward rotation |
| Debris fall | Nearly free fall of earth debris | From a vertical or overhanging face |
| Rockslide | Individual rock masses slide down bedding, joint or fault surfaces | Very fast and destructive on steep slopes; planar failure along steeply dipping discontinuities; affects material to a substantial depth |
| Rock fall | Free fall of rock blocks, keeping clear of the slope | From the surface layers of a rock face only |
Reading NCERT Figure 5.5 — Landslide scars, Shiwalik Himalaya (page 42)
- A photo of steep Shiwalik slopes near the river Sarada on the India–Nepal border, with long, pale, bare landslide scars running down between strips of forest — fresh rock and debris exposed where the surface has slid away.
- It illustrates the text's point that steep slopes + soft, young rocks (the Shiwaliks are made of weakly consolidated sediments) give frequent slides.
- Two NCERT slips: the text twice says ‘Figure 5.5 shows the relationships among different types of mass movements, their rates and moisture limits’ — that chart is missing; Figure 5.5 is only this photo. And the caption says ‘Uttar Pradesh’: the Sarada (Sharda) leaves the Shiwaliks near Tanakpur, which has been in Uttarakhand since 2000 (Beyond NCERT).
| Why landslides are frequent (NCERT box) | Himalayas | Western Ghats and Nilgiris |
|---|---|---|
| Tectonics | Tectonically active | Relatively stable |
| Rocks | Mostly sedimentary rocks and unconsolidated / semi-consolidated deposits | Mostly very hard rocks |
| Slopes | Very steep | Many slopes even steeper — almost vertical cliffs and escarpments |
| Weathering and rain | — | Strong mechanical weathering from temperature changes; heavy rain over short periods |
| Result | Debris avalanches and landslides very frequent | Less frequent, but direct rock falls along with landslides and debris avalanches |
Beyond NCERT — the full mass-movement family (from the earlier edition)
- Slow movements: creep (imperceptibly slow downslope movement of soil — bent fences and tilted poles show it) and solifluction (slow flow of water-saturated soil, common in cold regions over frozen ground).
- Rapid flow movements: earthflow, mudflow (very wet, often on volcanic slopes after rain) and debris avalanche (fast, in narrow steep tracks — common in humid areas with or without vegetation). NCERT's exercise Q1-iii expects debris avalanche under rapid flow mass movements.
- Landslides (dry, rapid): as in the table above. Subsidence: vertical sinking of the ground.
- India's Landslide Atlas (ISRO, 2023) and the NDMA's National Landslide Risk Management Strategy (2019) — asked in GS3 2021.
⤵ How a monsoon landslide happens
A steep slope of weak or jointed rockyoung sediments (Himalaya) or vertical cliffs (Western Ghats)
Support removed or slope loadedroad cutting at the toe, extra buildings, deforestation
Heavy rain soaks the slopesaturation, lubrication and extra weight
Disturbing force > shearing resistancethe trigger can be rain, an earthquake or blasting
Mass moves rapidly downslopeslump, debris slide, rockslide or rock fall
Exam trapMass movement is not erosion — gravity alone moves the material; no agent carries it. Landslides involve relatively dry material; flows are wet. A rock fall comes from the surface layer, a rockslide goes deep.
6. Erosion and deposition
In simple wordsWeathering breaks the rock into crumbs; erosion is the broom that sweeps them away; deposition is where the broom gets tired and drops them. The heavier crumbs drop first.
Erosion is the acquisition and transportation of rock debris by agents — running water, groundwater, glaciers, wind and waves — each according to its own dynamics. Debris carried by them grinds other rock (abrasion), aiding erosion. Erosion degrades relief; it is largely responsible for the continuous change of the earth's surface. Weathering aids erosion but is not a pre-condition for it. Weathering, mass wasting and erosion are all degradational processes, and erosion and transportation are driven by kinetic energy.
| Agent | State of matter | Controlled by |
|---|---|---|
| Wind | Gas | Climate |
| Running water | Liquid | Climate |
| Glaciers | Solid | Climate |
| Waves | — | Location — the coast, where lithosphere meets hydrosphere |
| Groundwater | — | Rock type (lithology) — karst forms only where rocks are permeable and soluble and water is available |
Deposition is a consequence of erosion: on gentler slopes the agents lose velocity and energy, so their load settles — coarser material first, finer later — filling depressions. NCERT says deposition is ‘not actually the work of any agent’, yet also calls the same agents ‘aggradational or depositional agents’: the point is that dropping the load is what happens when the agent stops working, not a separate effort.
⤵ The life of a rock fragment
Weatheringrock broken or decomposed in place
Mass movementgravity alone shifts it downslope
Erosionan agent picks it up (acquisition)
Transportationby water, ice, wind, waves or groundwater, using kinetic energy
Depositionagent slows on gentler slopes; coarse first, fine later
Aggradationdepressions filled — new landforms (Chapter 6)
Exam trapOf the five agents, only wind, running water and glaciers are controlled by climate. Waves depend on coastal location; groundwater on rock type (karst needs permeable, soluble rock).
7. Soil formation and the five soil-forming factors
In simple wordsMaking soil is like making curd from milk: you need the milk (parent material), the right warmth and time, and the bacteria to do the work. Change any one and you get a different result — or none at all.
Soil is a dynamic medium in which chemical, physical and biological activity goes on constantly. It is a product of decay and also a medium for growth — a changing, developing body whose properties shift with the seasons. Pedology is soil science; a pedologist is a soil scientist.
⤵ How a soil develops (pedogenesis)
Weathering mantle or transported depositsthe basic input — no weathered material, no soil
Pioneers colonisebacteria, mosses and lichens; minor organisms shelter inside
Humus builds upfrom dead organisms and plants
Grasses and ferns, then bushes and treesseeds brought by birds and wind
Roots and burrowers work the massit becomes porous and sponge-like — holds water, lets air pass
A mature soila complex mixture of mineral and organic matter
| Factor | Type | How it works (NCERT) |
|---|---|---|
| Parent material | Passive | In-situ weathered debris (residual soils) or transported deposits (transported soils); texture, structure and mineral/chemical make-up matter. Similar rocks can give different soils and vice versa, but young soils and some limestone soils show a clear link to the parent rock |
| Topography | Passive | Controls exposure to sunlight and surface/sub-surface drainage. Thin soils on steep slopes, thick on flat uplands; gentle slopes with slow erosion and good percolation are best; flat areas may build thick, dark clay rich in organic matter |
| Climate | Active | Moisture (intensity, frequency and duration of precipitation; evaporation; humidity) and temperature (seasonal and daily). See the climate diagram below |
| Biological activity | — | Adds organic matter, moisture retention, nitrogen. Dead plants → humus; organic acids from humification help decompose minerals; bacteria fix nitrogen; ants, termites, earthworms, rodents rework the soil |
| Time | — | Decides maturity and profile development. Soils on fresh alluvium or glacial till are young, with no or weak horizons; no fixed time can be given for maturity |
| Climate effect | Where | What happens |
|---|---|---|
| Eluviation / illuviation | Wherever water is in excess | Water carries soil components down (eluviation) and deposits them lower down (illuviation) |
| Desilication | Wet equatorial, high rainfall | Not only Ca, Na, Mg and K but most of the silica is removed |
| Hardpans | Dry climates | Evaporation > precipitation; groundwater rises by capillary action, evaporates and leaves salt crusts |
| Kanker | Tropical, intermediate rainfall | Calcium carbonate nodules form |
| Temperature | All | Chemical activity rises with heat, falls with cold (except carbonation) and stops when frozen: deep profiles in the tropics, mainly mechanically broken material in the tundra |
| Bacteria and humus | Cold climates | Humid tropics |
|---|---|---|
| Bacterial activity | Slow | Intense |
| Humus | Accumulates; undecomposed matter forms peat (sub-arctic, tundra) | Dead vegetation rapidly oxidised → very low humus |
Beyond NCERT
- NCERT calls time ‘the third important controlling factor’ although it is listed fifth, and a question box calls time, topography and parent material ‘passive’ while the text labels only the first two. The common reading: climate (and life) are active — they supply energy and do the work; parent material, topography and time are passive — they only set the conditions.
- Rhizobium lives in root nodules of legumes (beans, peas, pulses) — why pulses enrich soil with nitrogen (UPSC 1979). Earthworms improve soil structure and fertility but do not fix nitrogen (UPSC 1988).
- Heavy leaching removes basic cations (Ca, Mg, K, Na) and makes soils acidic (UPSC 1979). Desilication with iron and aluminium oxides left behind gives laterite — and bauxite (aluminium ore) by enrichment.
Exam trapTropical rainforest soils are poor in humus and nutrients despite lush forest — heat and moisture let bacteria decompose dead matter fast (UPSC 2023). Humus piles up in cold climates (peat).
NCERT's in-text questions — short answers
The chapter is full of grey question boxes. These are quick model answers.
Is it essential to distinguish geomorphic agents and geomorphic processes?
Yes, conceptually: a process is a force acting on materials (e.g. weathering, gravity stress); an agent is a moving medium that removes, carries and deposits (e.g. a river). Mass movement is a process with no agent; erosion needs an agent. For everyday exogenic work the terms overlap.
Epeirogeny and orogeny — cite the differences.
Orogeny: mountain building, severe folding, long narrow belts. Epeirogeny: continent building, uplift or warping of large areas, simple deformation.
What do the words volcanism and volcanoes indicate?
Volcanism = the whole process of magma moving onto or towards the surface and forming intrusive and extrusive forms. Volcano = a vent or landform through which material actually erupts.
Why do you think slopes or gradients are created by tectonic factors?
Endogenic forces — folding, faulting, uplift, volcanism — raise some areas and lower others, creating the slopes down which gravity and agents then move material.
What is the sole driving force behind all the exogenic processes?
The sun's energy, acting through the atmosphere (heat, winds, evaporation, rain).
Is the little motion that sometimes occurs in weathering synonymous with transportation?
No. Weathering may loosen or shift particles slightly, but nothing carries them away; transportation needs an agent moving material over a distance.
Between ‘mass wasting’ and ‘mass movements’, which is more appropriate? Can solifluction be a rapid flow?
‘Mass movements’ describes what happens (movement under gravity) without implying loss; ‘mass wasting’ stresses the wearing away of slopes. Solifluction is normally slow (saturated soil creeping over frozen ground) — it can speed up when thaw and heavy saturation combine, but it is classed as slow (Beyond NCERT detail).
Can you compare the three climatically controlled agents?
Wind (gas) — strongest in dry, bare areas; running water (liquid) — strongest in humid areas; glaciers (solid) — in cold high-latitude and high-altitude areas. All three erode, transport and deposit.
Mass movements and erosion both shift material. Why not treat them as one? Can there be erosion without weathering?
Mass movement is gravity alone; erosion needs a mobile agent. Yes — agents can erode fresh rock directly (e.g. abrasion by a river's load), though weathering makes erosion much easier.
Is weathering solely responsible for soil formation?
No. It supplies the parent material, but soil forms only when organisms, climate, topography and time act on it (pedogenesis).
Is it necessary to separate the process of soil formation and the soil-forming factors?
Yes: the process is the sequence of events (colonisation, humus, roots, mature soil); the factors are the controls that decide how fast and in which direction that sequence goes.
Why are time, topography and parent material considered passive control factors?
They do not supply energy or do any work themselves; they only set the conditions within which climate and organisms act.
NCERT exercise — answer outlines
The three multiple-choice questions are in the Self-check below. Try each written question yourself first, then open the outline to compare.
2(i) It is weathering that is responsible for bio-diversity on the earth. How? (30 words)
Weathering builds the weathering mantle and soil; the depth of this mantle decides the type and density of forests (vegetation), and biomes and biodiversity rest on vegetation. Deep tropical mantles carry the richest forests.
2(ii) What are mass movements that are real rapid and perceptible? List. (30 words)
Landslides: slump, debris slide, debris fall, rockslide, rock fall. Also the rapid flows — earthflow, mudflow and debris avalanche (Beyond NCERT in the current reprint).
2(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform? (30 words)
Running water, groundwater, glaciers, wind, waves and currents. Their prime job is erosion — acquiring and transporting debris — and then depositing it, thus degrading relief and filling depressions.
2(iv) Is weathering essential as a pre-requisite in the formation of soils? Why? (30 words)
Yes. Pedogenesis ‘depends first on weathering’: the weathering mantle (or transported weathered deposits) is the basic input on which organisms, climate and time then build a soil.
3(i) “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss. (150 words)
Intro: endogenic and exogenic processes.
Endogenic (energy from radioactivity, tidal and rotational friction, primordial heat): diastrophism — orogeny, epeirogeny, earthquakes, plate tectonics — and volcanism; they build relief unevenly.
Exogenic (sun's energy + tectonic gradients + gravity): weathering, mass movement, erosion, deposition; they degrade highs and aggrade lows.
The contest: exogenic forces would level the land, but endogenic forces keep raising it, so relief persists; rates vary with climate and rock structure.
Examples: the rising Himalaya being cut by rivers and landslides; the stable Peninsula worn into plateaus.
Conclude: today's landscape is a snapshot of this ongoing contest. Add the build-up vs wear-down sketch.
Endogenic (energy from radioactivity, tidal and rotational friction, primordial heat): diastrophism — orogeny, epeirogeny, earthquakes, plate tectonics — and volcanism; they build relief unevenly.
Exogenic (sun's energy + tectonic gradients + gravity): weathering, mass movement, erosion, deposition; they degrade highs and aggrade lows.
The contest: exogenic forces would level the land, but endogenic forces keep raising it, so relief persists; rates vary with climate and rock structure.
Examples: the rising Himalaya being cut by rivers and landslides; the stable Peninsula worn into plateaus.
Conclude: today's landscape is a snapshot of this ongoing contest. Add the build-up vs wear-down sketch.
3(ii) Exogenic geomorphic processes derive their ultimate energy from the sun's heat. Explain. (150 words)
Intro: exogenic processes draw energy from the atmosphere, driven by the sun, plus slopes made by tectonics.
Weathering: solar heating causes expansion–contraction and drives the water cycle that supplies water for chemical reactions; temperature controls their speed.
Running water and glaciers: the sun evaporates water; rain and snow feed rivers and ice that erode.
Wind: unequal solar heating creates pressure differences and winds.
Waves: generated by winds.
Biological activity: plants grow on solar energy.
Gravity's role: it acts on slopes, but the sun supplies the moving media.
Climatic control: latitudinal, seasonal and land–sea differences in solar energy make processes vary by region (Figure 5.2).
Conclude: without the sun, there would be no agents to wear the land down.
Weathering: solar heating causes expansion–contraction and drives the water cycle that supplies water for chemical reactions; temperature controls their speed.
Running water and glaciers: the sun evaporates water; rain and snow feed rivers and ice that erode.
Wind: unequal solar heating creates pressure differences and winds.
Waves: generated by winds.
Biological activity: plants grow on solar energy.
Gravity's role: it acts on slopes, but the sun supplies the moving media.
Climatic control: latitudinal, seasonal and land–sea differences in solar energy make processes vary by region (Figure 5.2).
Conclude: without the sun, there would be no agents to wear the land down.
3(iii) Are physical and chemical weathering processes independent of each other? If not, why? Explain with examples. (150 words)
No — they work together; one usually dominates.
Physical helps chemical: cracking and granular disintegration expose more surface to water and air — e.g. frost-shattered granite rots faster; unloading joints let water in.
Chemical helps physical: hydration makes minerals swell and crack rock; solution weakens cements so grains fall apart; oxidation weakens iron-rich rocks.
Biology links both: roots wedge rocks apart (physical) and release acids (chemical); burrowers open new surfaces to chemical attack.
Climate decides the balance: hot and wet → chemical dominant, deep mantle; cold or dry → physical dominant, thin mantle (Figure 5.2).
Conclude: NCERT: very rarely does any one process operate by itself.
Physical helps chemical: cracking and granular disintegration expose more surface to water and air — e.g. frost-shattered granite rots faster; unloading joints let water in.
Chemical helps physical: hydration makes minerals swell and crack rock; solution weakens cements so grains fall apart; oxidation weakens iron-rich rocks.
Biology links both: roots wedge rocks apart (physical) and release acids (chemical); burrowers open new surfaces to chemical attack.
Climate decides the balance: hot and wet → chemical dominant, deep mantle; cold or dry → physical dominant, thin mantle (Figure 5.2).
Conclude: NCERT: very rarely does any one process operate by itself.
3(iv) How do you distinguish between the process of soil formation and soil-forming factors? What is the role of climate and biological activity? (150 words)
Process = the sequence by which soil develops: weathered material → colonisation by bacteria, mosses, lichens → humus → grasses, bushes, trees → porous, sponge-like mature soil. Factors = the controls on that sequence: parent material, topography, climate, biology, time.
Climate (active): moisture drives chemical and biological activity, eluviation–illuviation, desilication in wet tropics, hardpans in dry lands, kanker in intermediate areas; temperature speeds or stops reactions — deep tropical profiles, mechanically broken tundra soils.
Biological activity: adds organic matter and humus, retains moisture, fixes nitrogen (Rhizobium in legumes); bacterial speed decides humus — peat in cold climates, little humus in the humid tropics; ants, termites, earthworms mix the soil.
Conclude: factors act together; climate and life do the work, others set the stage.
Climate (active): moisture drives chemical and biological activity, eluviation–illuviation, desilication in wet tropics, hardpans in dry lands, kanker in intermediate areas; temperature speeds or stops reactions — deep tropical profiles, mechanically broken tundra soils.
Biological activity: adds organic matter and humus, retains moisture, fixes nitrogen (Rhizobium in legumes); bacterial speed decides humus — peat in cold climates, little humus in the humid tropics; ants, termites, earthworms mix the soil.
Conclude: factors act together; climate and life do the work, others set the stage.
Project work: observe and record the climate, weathering process and soil around you
Note the local rainfall and temperature pattern; look for signs of weathering (cracked or flaking rock, rust stains, roots in cracks, crumbling walls); dig a small pit and record soil colour, texture (sand/silt/clay feel), roots and humus, and any layers. Link what you see to the factors: parent rock, slope, climate, organisms, time.
What to remember
Numbers
Sources of endogenic energy3 — radioactivity · rotational & tidal friction · primordial heat
Components of diastrophism4 — orogeny, epeirogeny, earthquakes, plate tectonics
Denudational processes in Figure 5.13 — weathering, mass movement, erosion/transport
Groups of weathering3 — chemical, physical, biological
Chemical weathering processes named5 — solution, carbonation, hydration, oxidation, reduction
Forms of mass movement3 — heave, flow, slide
Activating causes of mass movement9
Types of landslide in the text5 — slump, debris slide, debris fall, rockslide, rock fall
Erosional agents5 — wind, running water, glaciers, waves, groundwater
Climate-controlled agents3 — wind (gas), water (liquid), glacier (solid)
Soil-forming factors5
Tropical forest rainfall in Figure 5.2> 3,000 mm
Weathering mantle zones in Figure 5.26
Strakhov's diagram1967
One-liners
- Endogenic = land building; exogenic = land wearing.
- Degradation wears highs down; aggradation fills lows; gradation = wearing down by erosion.
- Orogeny = mountain building; epeirogeny = continent building.
- PVT changes from diastrophism cause metamorphism.
- Weathering is in situ; erosion needs an agent; mass movement needs only gravity.
- Exfoliation is a result, not a process.
- Exfoliation domes ← unloading; tors ← thermal expansion.
- Weathering enriches ores of iron, manganese, aluminium, copper.
- Coarse material is deposited first, fine later.
- Wet tropics: desilication, low humus. Dry lands: hardpans. Cold: peat.
- Rhizobium in legume root nodules fixes nitrogen.
Traps to avoid
- Volcanism and diastrophism are endogenic, not exogenic.
- Mass movement is not erosion — no agent is involved.
- Weathering aids but is not a pre-condition for erosion or mass movement — yet it is essential for soil.
- Landslides are rapid and involve relatively dry material.
- Slump has backward rotation; debris slide has none.
- Rock fall: surface layers only; rockslide: substantial depth.
- Waves and groundwater are not controlled by climate.
- Chemical activity slows in cold — except carbonation.
- Humus accumulates in cold climates; it is low in the humid tropics.
- NCERT's ‘Figure 6.1/6.2’ in this chapter mean Figures 5.1/5.2.
How to strategise
Prelims — what UPSC asks
- Process-level statements: rain causes weathering because it carries dissolved CO₂ and O₂ — carbonation and oxidation (2024). Learn what each chemical process needs.
- Soil biology and chemistry: humus is organic matter of plant and animal origin (1986); leaching of bases makes soils acidic (1979); legumes like beans fix nitrogen (1979); earthworms are useful but do not fix nitrogen (1988); tropical rainforest soil is poor because decomposition is fast (2023).
- Link to Indian soils: desilication and Fe–Al oxides explain laterite and red soils; kanker and hardpans explain arid soils. India-soil questions (laterite, red soil colour) are frequent — read this chapter's climate table with the soils chapter of India: Physical Environment.
Mains — where it appears and how to answer
- GS1 favourite: landslides in the Himalayas vs the Western Ghats — asked in 2013, 2016 (with mitigation) and 2021. The NCERT box is the skeleton: tectonics, rock type, slope, weathering, rainfall. Add human causes (road cutting, deforestation, hydro projects, unplanned building) and examples (Kedarnath 2013, Joshimath land subsidence 2023, Wayanad 2024 — Beyond NCERT).
- GS3 (Disaster management): landslide hazard zonation mapping (2019) and the causes, effects and National Landslide Risk Management Strategy (2021). Use the nine activating causes as your ‘causes’ list.
- Answer frame: define (gravity-driven mass movement) → types (slump, slide, fall, flow) → natural causes → human triggers → regional contrast → impacts → mitigation (zonation maps, early warning, slope engineering, drainage, afforestation, building codes).
- Diagrams that score: a slump cross-section, the Himalaya vs Western Ghats table, and Figure 5.2's weathering-depth sketch for questions on soils and climate.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. Which one of the following processes is a gradational process?
2. Which one of the following materials is affected by hydration process?
3. Debris avalanche can be included in the category of:
4. Which force drives mass movements, according to NCERT Figure 5.1?
5. In NCERT Figure 5.2, the deepest weathering mantle is found under…
6. Exfoliation domes and tors result respectively from…
7. Why do soils of humid equatorial regions have little humus?
UPSC questions from this chapter
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