"Erosion" is searched about 5,900 times a month in Australia (with "what is erosion" another 2,400), 3,300 in Canada and 2,900 in the UK, by Year 4 and Year 8 students in Australia whose curriculum names it twice, by Grade 4 and Grade 7 students in the US and Canada, and by KS3 and GCSE Geography students in England. The idea is simple and the vocabulary is large. This page gives the difference between weathering, erosion and deposition, the three types of weathering with examples, the five agents of erosion with the processes and the landforms each produces, soil erosion and its prevention, how fast it all happens, the curriculum placements, and a printable chart with practice.
Download the weathering and erosion chart with practice (PDF) (A4, the weathering types and the agents-and-landforms chart on page 1, prevention, rates and the practice set with answers on page 2, free).
Three words, three stages
| Word | What happens | Movement? | Example |
|---|---|---|---|
| Weathering | rock is broken down or changed where it is | no | frost cracks a boulder; limestone dissolves in rain |
| Erosion | the loosened rock and soil are worn away and carried off | yes | a river carries sand downstream; wind blows soil off a field |
| Deposition | the carried material is dropped when the agent slows | the end of the movement | a delta forms where a river meets the sea; a dune forms where the wind drops |
Weathering supplies the material, erosion transports it, deposition builds new landforms with it. Together they lower mountains and fill seas: the Appalachians were once as high as the Himalayas.
The types of weathering
Physical (mechanical) weathering
Rock breaks into smaller pieces of the same stuff.
- Freeze-thaw (frost shattering): water gets into a crack, freezes, expands by about 9 percent and widens the crack; repeated hundreds of times it splits the rock. Scree slopes below cliffs in cold mountains are its product.
- Exfoliation (onion-skin weathering): rock surfaces heat and expand by day and cool and contract by night, and outer layers peel off in sheets. Common in deserts and on granite domes.
- Salt crystal growth: salty water evaporates in pores, crystals grow and prise grains apart. Coasts and deserts.
- Abrasion: rock scraped by other rock carried in wind, water or ice (also counted as an erosion process).
- Pressure release: rock that formed deep underground expands and cracks as the rock above is removed.
Chemical weathering
The minerals themselves change.
- Carbonation: rainwater absorbs carbon dioxide and becomes weak carbonic acid, which dissolves limestone and chalk: caves, limestone pavements, sinkholes, and the pitted look of old gravestones. Acid rain speeds it up.
- Oxidation: oxygen (with water) reacts with iron minerals and rusts them; red and brown rock surfaces and soils.
- Hydrolysis: water reacts with minerals such as feldspar in granite to form clay, which crumbles. The china clay of Cornwall.
- Solution: some minerals (rock salt, gypsum) simply dissolve in water.
Chemical weathering is fastest in hot, wet climates, physical weathering in cold or dry ones.
Biological weathering
Living things do the work: roots grow into cracks and widen them; burrowing animals (rabbits, worms, ants) expose rock to air and water; lichens, mosses and bacteria release acids that dissolve minerals; people quarry, dig and walk paths bare.
The five agents of erosion, and the landforms they make
| Agent | How it erodes | Landforms of erosion | Landforms of deposition |
|---|---|---|---|
| Running water (rivers, rain run-off) | hydraulic action (the force of the water), abrasion (the load scraping the bed and banks), attrition (the load grinding itself smaller and rounder), solution | V-shaped valleys, gorges, waterfalls and plunge pools, meanders (eroding the outer bank), gullies and rills on bare slopes | floodplains, levees, deltas, alluvial fans, point bars on the inner bank |
| Wind | deflation (lifting loose grains), abrasion (sandblasting) | desert pavements, mushroom rocks (pedestal rocks), yardangs, blowouts | sand dunes (barchans, seifs), loess (wind-blown silt) |
| Ice (glaciers) | plucking (freezing onto rock and tearing it out), abrasion (rock in the ice grinding the bed) | U-shaped valleys, corries (cirques), arêtes, pyramidal peaks, hanging valleys, fjords, striations | moraines, drumlins, erratics, outwash plains |
| Gravity (mass movement) | the pull of gravity on weathered material, often after rain | rockfalls, landslides, mudflows, slumps, soil creep (terracettes, bent trees) | scree slopes, landslide debris |
| Waves (the sea) | hydraulic action (air compressed in cracks), abrasion, attrition, solution | cliffs, wave-cut platforms, headlands and bays, caves, arches, stacks and stumps (Durdle Door, the Twelve Apostles) | beaches, spits, bars, tombolos, salt marshes behind spits |
Running water is the chief sculptor of most landscapes; ice shaped the north of Europe and North America in the last ice age (the Great Lakes, the Lake District, the fjords); wind rules where plants are absent; waves work only at the coast but never stop.
Soil erosion: causes and prevention
Soil forms at about 1 cm every 100 to 400 years and can be lost in a single storm once it is bare. The causes are almost all the removal of plant cover: deforestation, overgrazing, ploughing up and down slopes, leaving fields bare between crops, construction and off-road vehicles, and the drying of soils in drought (the American Dust Bowl of the 1930s, the Australian dust storms of 2009 and 2019).
| Method | How it works | Where |
|---|---|---|
| Contour ploughing | furrows follow the contours and hold water instead of channelling it downhill | sloping fields |
| Terracing | steps turn a steep slope into flat fields | hillsides (rice terraces, vineyards) |
| Cover crops and stubble | roots hold soil and leaves break the rain's impact between main crops | all arable land |
| No-till farming | seed is drilled into last year's residue; the soil is never bared | large-scale grain farming |
| Mulching | straw or bark covers bare soil | gardens, orchards |
| Windbreaks and shelterbelts | rows of trees slow the wind | flat, open farmland |
| Buffer strips | grass or trees along streams trap sediment and run-off | riverbanks |
| Reforestation | roots and canopy restore the cover | degraded slopes |
| Dune grasses (marram), fencing, boardwalks | roots bind sand; people kept off | coastal dunes |
| Groynes, sea walls, rock armour, gabions | trap beach sand; absorb wave energy | coasts |
Preventing erosion is cheaper than repairing it: lost topsoil takes centuries to rebuild.
How fast does it happen?
| Process | Typical rate |
|---|---|
| Soil loss from a bare ploughed slope | 10 to 100 tonnes per hectare a year (several millimetres of soil) |
| Soil formation | about 1 cm per 100 to 400 years |
| Niagara Falls retreating | about 30 cm a year now (over a metre a year before flow control) |
| Soft cliffs on England's Holderness coast | 1 to 2 m a year, the fastest in Europe |
| Mountain ranges lowered by erosion | tens of centimetres per thousand years |
| The Grand Canyon's depth | 1.8 km cut by the Colorado River in about 5 to 6 million years |
The mistakes that cost marks
- Using weathering and erosion as the same word. Weathering stays put; erosion moves.
- Calling a landslide weathering. Gravity moving material is erosion (mass movement).
- Saying limestone is "worn away by rain". It is dissolved: chemical weathering by carbonation.
- Giving "water" as an agent without the process (hydraulic action, abrasion, attrition, solution are the mark-scheme words).
- Forgetting deposition: a delta or a beach is not erosion; it is what erosion builds elsewhere.
- Listing a prevention method without saying how it works (contour ploughing "holds water on the slope").
Where it sits in each curriculum
| Curriculum | When | What is expected |
|---|---|---|
| Australia | Year 4 (AC9S4U02: Earth's surface changes over time as a result of natural processes and human activity, including weathering and erosion), Year 8 (the rock cycle: weathering, erosion, deposition in forming sedimentary rock), Year 9 and 10 Geography | agents, landforms, prevention in Year 4; the rock cycle in Year 8 |
| US (NGSS) | Grade 2 (2-ESS1-1, 2-ESS2-1: wind and water change the land; solutions to slow it), Grade 4 (4-ESS2-1: effects of weathering and the rate of erosion by water, ice, wind or vegetation), middle school (MS-ESS2-2) | the agents with evidence; design a solution |
| England | KS3 (the rock cycle; weathering), KS3 and GCSE Geography (rivers and coasts: the four erosion processes, landforms, management) | processes named, landforms explained, management evaluated |
| India (CBSE) | Class 7 Geography (Our Changing Earth: weathering, erosion, the work of rivers, sea waves, ice and wind, with landforms), Class 9 and 10 Geography (soil erosion and conservation) | the agents and landforms in Class 7; conservation in Class 10 |
| Canada (Ontario) | Grade 7 (Earth's crust: weathering, erosion, deposition), Grade 8 (water systems) | the three words and the agents |
Practice (answers in the PDF)
- Explain the difference between weathering and erosion with one example of each.
- Classify each as physical, chemical or biological weathering: a root cracking a pavement; a gravestone's letters fading; a boulder splitting after a frosty winter; red stains on a sandstone cliff.
- Name the four ways a river erodes its channel.
- Match the landform to the agent: U-shaped valley; sand dune; arch and stack; delta; landslide.
- A farmer's sloping field loses soil every rainy season. Suggest three measures and say how each works.
- Why is soil erosion a bigger problem than its slow rate suggests?
Download the chart and the practice set (PDF)
Where to get help
A 1-on-1 online science class in Australian, UK, Canadian and US after-school hours with a tutor who teaches the Australian Years 4 to 10, KS3 and GCSE science and geography, NGSS Grade 2 to 8 and CBSE Class 7 to 10 every week: landforms taught with photographs and a chart the child fills in, the process words attached to each picture until they come without prompting. The Earth science page lists the courses; the free 30-minute first class is a real lesson on this week's topic. Related pages: Earth's four spheres and types of ecosystems.
Questions parents ask
1What is erosion?
2What is the difference between weathering and erosion?
3What are the three types of weathering?
4What are the agents of erosion?
5How can erosion be prevented?
See how we teach this, 1-on-1 online →
Shobha
Founder and lead tutor, Science with Shobha
Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.