GeographyISC Class 11 · Weathering and Gradation

Physical, Chemical and Biological Weathering (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

Physical weathering breaks rock without changing its chemistry (exfoliation, block and granular disintegration, frost action, salt crystallisation) and dominates in deserts and cold highlands. Chemical weathering (solution and carbonation, oxidation, hydration, hydrolysis) changes minerals and dominates in hot, humid regions. Biological weathering is done by roots, animals, lichens and humans.

Physical weathering only breaks rock, chemical weathering changes its minerals, and biological weathering is done by living things such as roots.

Illustration drawn for QuestionBuddy.

Understand Physical, Chemical and Biological Weathering

Physical (mechanical) weathering.
1. Exfoliation: outer layers peel off in curved sheets when pressure is released and surfaces heat and cool; it forms rounded domes in granite (for example in parts of Karnataka and Tamil Nadu).
2. Block disintegration: daily heating and night cooling in hot deserts make rocks expand and contract, breaking them along joints into blocks.
3. Granular disintegration: in coarse-grained rocks such as granite, different minerals expand by different amounts and grains fall away.
4. Frost action: water in cracks freezes and expands by about 9 per cent, wedging the rock apart and making angular scree in cold regions and high mountains.
5. Salt crystallisation: salt crystals growing in pores force grains apart in deserts and on coasts.

Chemical weathering (most active in hot, humid climates).
1. Solution and carbonation: rainwater with carbon dioxide forms weak carbonic acid and dissolves limestone to soluble calcium bicarbonate, creating caves and karst.
2. Oxidation: oxygen combines with iron minerals to make iron oxides; rocks turn red, yellow or brown and crumble (red laterite).
3. Hydration: minerals absorb water, swell and weaken (anhydrite to gypsum).
4. Hydrolysis: water reacts with minerals such as feldspar to form clay minerals, the key change in decay of granite.

Biological weathering. Plant roots widen cracks; burrowing animals (earthworms, rodents, termites) loosen rock and soil; lichens and decaying vegetation release acids; human activity such as mining, quarrying, road-building and deforestation exposes rock to faster weathering.

Climate link. Large temperature ranges and sparse vegetation favour physical weathering; warmth and moisture favour chemical weathering.

Physical, Chemical and Biological Weathering: key facts

Physical types: Exfoliation
Block disintegration
Granular disintegration
Frost action
Salt crystallisation
Chemical types: Solution and carbonation
Oxidation
Hydration
Hydrolysis
Frost expansion: $I ce v o l u m e = 1.09 x w a t er v o l u m e ∣ A b o u t 9 p er ce n t in cr e a se$
Climate link: Deserts, cold regions: physical | Humid tropics: chemical

How to answer Physical, Chemical and Biological Weathering questions

Questions are 3 to 4 marks per type, with occasional frost-volume sums.

1Name the category and its basic distinction.
2Describe each process with one clear cause and one example.
3Mention the climate where it dominates.
4For sums, write the formula, substitute and give the volume in cm3.

Physical, Chemical and Biological Weathering in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Frozen bottle

Suppose a sealed glass jar of 200 cm3 of water freezes in a freezer.

What happens, and what volume does the ice need?

Try it first, then show the solutionSolution

Water expands about 9 per cent on freezing.
Ice volume = 200 x 1.09 = 218 cm3.

Answer: The ice needs 218 cm3, so the jar may crack.

Memory hook: Water swells 9 per cent as ice.

Rusting rock

Suppose a hillside of iron-rich rock turns reddish-brown after rainy seasons.

Which chemical process is responsible?

Try it first, then show the solutionSolution

Oxygen combines with iron minerals.
This oxidation forms iron oxides, giving red or brown colours.

Answer: Oxidation.

Memory hook: Rust is oxidation.

Tricks to remember Physical, Chemical and Biological Weathering

Short memory aids. Say each one aloud once, then use it on a question the same day.

FBGSE
Frost, Block, Granular, Salt, Exfoliation: five physical processes.
Use it when: Physical list.
SOHH
Solution (carbonation), Oxidation, Hydration, Hydrolysis.
Use it when: Chemical list.

Physical, Chemical and Biological Weathering: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Colour change · 1 mark · MCQBoard level

Rocks turn red or brown mainly due to:
(a) carbonation
(b) hydration
(c) oxidation
(d) exfoliation

Try it first, then show the solutionSolution

Iron and oxygen.

Answer: (c) Oxidation.

Example 2: Process matching · 3 marks · Short answerBoard level

Match each process to its example: (a) carbonation, (b) hydrolysis, (c) hydration.

Try it first, then show the solutionSolution

(a) Limestone dissolved to calcium bicarbonate.
(b) Feldspar changing to clay.
(c) Anhydrite changing to gypsum.

Answer: (a) Limestone dissolving (b) feldspar to clay (c) anhydrite to gypsum.

Example 3: Frost wedging sum · 4 marks · Long answerHarder board level

A crack contains 50 cm3 of water that freezes and expands by 9 per cent. Find the volume of ice and the extra volume.

Try it first, then show the solutionSolution

Ice volume = 50 x 1.09 = 54.5 cm3.
Extra volume = 54.5 - 50 = 4.5 cm3.
This extra volume pushes against the walls of the crack.
Repeated freezing and thawing shatters rock into scree.

Answer: 54.5 cm3 of ice; 4.5 cm3 extra.

Example 4: Climate contrast · 4 marks · Long answerHarder board level

Explain why chemical weathering dominates in the humid tropics but physical weathering in hot deserts and cold highlands.

Try it first, then show the solutionSolution

Chemical processes need warmth and water; humid tropics supply both.
Deserts have large daily temperature ranges and little water, favouring expansion and contraction.
Cold highlands have freeze-thaw cycles and sparse vegetation.
So the dominant type follows temperature range and moisture.

Answer: Warm, wet climates favour chemical change; large temperature ranges and dryness or frost favour physical breakage.

Example 5: Apply to a case · 5 marks · Case-basedHOTS / competency

Case (invented): A limestone region has caves and a nearby granite hill shows rounded domes. (a) Name the process forming the caves and its chemistry. (b) Name the process forming domes. (c) Say which of the two also produces clay from feldspar and name that process.

Try it first, then show the solutionSolution

(a) Solution and carbonation: carbonic acid from rainwater with CO2 dissolves limestone into calcium bicarbonate.
(b) Exfoliation, helped by release of pressure and heating and cooling.
(c) Hydrolysis acts on the granite.

Answer: (a) Carbonation (b) exfoliation (c) hydrolysis of feldspar.

Where students lose marks in Physical, Chemical and Biological Weathering

The slips examiners see most often, and what to write instead.

Mistake: Mixing oxidation and hydration
Two chemical processes are swapped.
Do this: Oxidation uses oxygen with iron; hydration adds water to minerals.
Usually costs: 1 mark.
Mistake: Expansion figure wrong
9 per cent is forgotten or applied twice.
Wrong working
50 x 0.09 = 4.5 as ice volume
Right working
50 x 1.09 = 54.5 cm3 ice
Do this: Ice volume = 1.09 x water volume.
Usually costs: 2 marks.
Mistake: Saying frost action is chemical
Category mistake.
Do this: Frost action is physical weathering.
Usually costs: 1 mark.

Exam tips

List all four chemical processes with one example each.
Link each process to a climate.
Show 1.09 in frost sums.
Name granite for exfoliation and limestone for carbonation.

Practice questions on Physical, Chemical and Biological Weathering

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Frost action is most common in:
(a) equatorial forests
(b) high mountains and cold regions
(c) river deltas
(d) coral reefs
Hint
Freeze-thaw.
Answer
(b) High mountains and cold regions.
Q2 · 3 marks · Short answerHarder board level
A crack holds 250 cm3 of water that expands by 9 per cent on freezing. Find the volume of ice.
Hint
250 x 1.09.
Answer
250 x 1.09 = 272.5 cm3; the extra volume is 22.5 cm3.
Q3 · 4 marks · Long answerHarder board level
Explain biological weathering with four examples.
Hint
Roots, animals, lichens, humans.
Answer
Plant roots widen cracks; burrowing animals loosen rock and soil; lichens and decaying plants release acids; mining, quarrying, road-building and deforestation expose rock to faster weathering.
Q4 · 3 marks · Short answerHarder board level
Distinguish between block disintegration and granular disintegration.
Hint
Blocks versus grains.
Answer
Block disintegration breaks rock along joints into blocks by repeated expansion and contraction; granular disintegration loosens individual mineral grains because minerals expand unequally.
Q5 · 4 marks · Case-basedHOTS / competency
Case: A coastal wall shows white salt crusts and crumbling stone. (a) Name the physical process. (b) Explain how it breaks stone. (c) Name another climate where it is common.
Hint
Crystals in pores.
Answer
(a) Salt crystallisation. (b) Salt-laden water evaporates in pores, crystals grow and force grains apart. (c) Deserts.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Cause of red colour?Show answer
Oxidation.
2.Process creating caves in limestone?Show answer
Solution and carbonation.
3.Process that turns feldspar into clay?Show answer
Hydrolysis.
4.Frost expansion?Show answer
About 9 per cent.
5.Rock fragments from frost action?Show answer
Angular scree.

Physical, Chemical and Biological Weathering: frequently asked questions

Does physical weathering change chemistry?

No, only the size of the pieces.

Do roots cause physical or chemical change?

Both, widening cracks and releasing acids.

Why is granite rounded?

Exfoliation peels layers like an onion.