Science
What is the difference between weathering and erosion?
Quick answer
Weathering breaks rocks down into smaller pieces where they are. Erosion picks those pieces up and carries them away, by water, wind, ice or gravity. Then deposition drops them somewhere new.
In one sentence
Weathering breaks rock into smaller pieces where it stands, and erosion carries those pieces away to somewhere else.
Explained
Rocks look as if they last for ever, but sun, rain, ice, wind and living things are slowly breaking them apart all the time. Scientists split this into two steps that are easy to mix up.
rock
rain
mountain
Weathering is the breaking down of rocks in place. Nothing moves yet: the rock just cracks, crumbles or changes. There are three kinds:
- Physical (mechanical) weathering breaks rock by force. In freeze-thaw, water gets into a crack, freezes and expands by about 9%, pushing the crack wider; when it thaws, more water gets in, and over many winters the rock splits. In deserts, rock heats up in the day and cools at night, and the outer layers can flake off like onion skin.
- Chemical weathering changes the minerals in the rock. Rainwater is slightly acidic because it dissolves carbon dioxide from the air, so it slowly dissolves limestone and chalk, making caves and hollows. Iron in rocks can react with oxygen and water, like rust, turning rock red and crumbly.
- Biological weathering is caused by living things. Plant roots grow into cracks and force them open, burrowing animals break up rock, and lichens make weak acids that eat into stone.
Erosion is the removal and transport of the weathered pieces. The four main agents are water (rain, rivers and sea waves), wind, ice (glaciers) and gravity (rockfalls and landslides). As the pieces travel, they knock against each other and against the ground, so they become smaller and rounder. That is why river pebbles are smooth.
Deposition comes next. When the river, wind or glacier slows down, it loses energy and drops its load. Rivers build deltas where they reach the sea, wind piles sand into dunes, and glaciers leave heaps of rock called moraines. Over millions of years, layers of deposited sediment can be pressed and cemented into new sedimentary rock: one part of the rock cycle.
So the order is: weathering → erosion (transport) → deposition. A simple way to remember it: weathering breaks, erosion takes, deposition drops.
Weathering is also how soil begins. Rock is broken into tiny particles, then mixed with humus (rotted plants and animals), air and water. Soil forms very slowly, which is why losing it to erosion is a serious problem for farmers.
Examples
| What you see | Process | Type or agent |
|---|---|---|
| A boulder split in two by ice in a crack | weathering | physical (freeze-thaw) |
| A tree root lifting a pavement or splitting a rock | weathering | biological |
| Caves in limestone, worn letters on an old marble gravestone | weathering | chemical |
| The Grand Canyon, cut by the Colorado River over millions of years | erosion | water |
| A U-shaped valley in the mountains | erosion | ice (a glacier) |
| Sand blown off a beach in a storm | erosion | wind |
| A delta at a river mouth, a sand dune | deposition | water, wind |
Worked example: a pebble on a beach. Rain and frost broke it off a cliff (weathering). A river and then the waves carried it along, rolling it smooth (erosion). Finally, a calm part of the shore dropped it there (deposition).
Common mistakes
- Thinking weathering and erosion are the same. Fix: ask "did it move?" If the rock is broken but still there, it is weathering. If the pieces are carried away, it is erosion.
- Thinking weathering has to do with the weather only. Plant roots, animals and chemical reactions weather rock too, not just rain and frost.
- Forgetting deposition. Erosion has to stop somewhere. Wherever the moving material is dropped, that is deposition.
- Thinking it is always slow. Most weathering and erosion take years to millions of years, but a landslide or a big flood can move huge amounts of rock in hours.
Step by step
Step by step
- Look at the rock or landWhat has changed? Is there a crack, a hole, a smooth pebble, a pile of sand?
- Ask "did it move?"Broken but still in place means weathering. Carried away means erosion. Dropped in a new place means deposition.
- For weathering, find the causeForce (ice, heat, salt) is physical. A change in the minerals (acid rain, rust) is chemical. Living things are biological.
- For erosion, find the agentWater, wind, ice or gravity.
- Join the storyPut the steps in order: weathering, erosion and transport, deposition.
Try a kitchen experiment: shake a few sugar cubes in a closed jar for two minutes and look at the sharp corners (physical weathering and wear). Then drop a piece of eggshell, or chalk made of calcium carbonate, into a glass of vinegar and watch it fizz: a model of chemical weathering, because limestone is calcium carbonate too. (Some chalk sticks are made of gypsum and will not fizz.)
Practice questions
Weathering, erosion or deposition?
Try each one, then check your answer.
- A rock cracks because water in it freezes. Weathering or erosion?
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Weathering (physical, freeze-thaw): the rock has not moved. - A river carries sand downstream. Weathering or erosion?
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Erosion: the material is being moved. - Wind drops sand at the back of a beach, building a dune. What is this called?
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Deposition - Moss and roots grow into the cracks of a wall and widen them. What kind of weathering is this?
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Biological weathering - Acidic rainwater dissolves limestone. What kind of weathering is this?
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Chemical weathering - Name the four main agents of erosion.
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Water, wind, ice and gravity - Why does freeze-thaw weathering need temperatures that go above and below 0 °C?
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Water must freeze to expand and thaw to let more water in, again and again. - Why are pebbles in a river round and smooth?
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They are rubbed and knocked against each other as they are carried along (erosion wears off the corners). - Put in order: deposition, weathering, erosion.
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Weathering, erosion, deposition - Why does a river drop its sediment when it reaches the sea?
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It slows down and loses energy, so it cannot carry its load any more. - A marble gravestone and a granite gravestone are both 150 years old. The marble one is much harder to read. Why?
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Marble is made of calcium carbonate, like limestone, so acidic rain dissolves it (chemical weathering) much faster than granite. - Which kind of physical weathering is most common in hot deserts?
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Heating and cooling: rock expands by day and contracts at night, so outer layers crack and peel off. - How does weathering help make soil?
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It breaks rock into tiny particles, which mix with humus, air and water to form soil. - A glacier carves a valley and leaves a pile of rocks at its end. Name the two processes.
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Carving the valley is erosion; leaving the pile (a moraine) is deposition.
Word problems
Weathering and erosion in real life
Try each one, then check your answer.
- Water expands by about 9% when it freezes. About how much ice does 100 mL of water in a crack become?
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100 + 9 = about 109 mL of ice, which pushes on the sides of the crack. - Suppose a soft clay cliff loses 0.5 m of land to the sea every year. How far will it retreat in 40 years?
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0.5 × 40 = 20 m - In a shaking experiment, sugar cubes weigh 30 g at the start and 24 g after shaking. What percentage was worn away?
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30 − 24 = 6 g; 6 ÷ 30 = 0.2 = 20% - The letters on an old gravestone were 6 mm deep in 1920 and are 4 mm deep in 2020. What was the average rate of weathering?
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2 mm in 100 years = 0.02 mm per year - Suppose a sand dune moves 15 m downwind each year. How long will it take to move 120 m?
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120 ÷ 15 = 8 years - A farmer's field is on a slope and the soil keeps washing away. Give two ways to reduce the erosion.
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For example: plant hedges, trees or grass, plough across the slope instead of up and down, or build terraces.
Questions people ask
What is weathering and erosion in simple words?
Weathering is rock breaking into pieces where it is. Erosion is those pieces being carried away by water, wind, ice or gravity.
How are weathering and erosion related?
They work together. Weathering makes the loose pieces; erosion moves them; deposition drops them somewhere new. Without weathering, there would be much less loose material for erosion to carry.
What is weathering, erosion and deposition?
They are three steps in the same story: break (weathering), take (erosion and transport), drop (deposition). Together they shape valleys, beaches, deltas and dunes.
How do weathering and erosion change the Earth's surface?
They wear mountains down, carve valleys and canyons, shape coastlines and caves, and build new land, such as deltas and beaches, from the material they drop.
How can we prevent weathering and erosion?
We cannot stop weathering, but we can slow erosion: plant trees, hedges and grass to hold soil, use terraces on hills, plough across slopes, and build sea walls or groynes on coasts.
What is a good weathering and erosion experiment for kids?
Shake sugar cubes in a jar (physical weathering), put eggshell or calcium-carbonate chalk in vinegar (chemical weathering), or pour water down a tray of sand propped at an angle to watch erosion and deposition happen.
Quick quiz
Weathering and erosion
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Question 1 of 5
What is the main difference between weathering and erosion?
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