GCSE-readyGeo 2026: Coasts introduction, waves and key words
A coastline is where the land meets the sea. It ranges from dramatic cliffs to fine sandy beaches and is always changing.
Key words for coasts
Weathering: the breakdown of rocks at or near the surface.
Erosion: waves wearing away rock along the coast.
Transportation: the movement of material along the coast. Suspension: fine material carried in the water.
Deposition: waves lose energy and drop the material they carry.
Mass movement: rock and soil moving down the cliff under gravity.
Hard engineering: built structures such as a sea wall. Soft engineering: working with nature, such as sand dune protection.
Storm surge: a rise in sea level caused by low pressure and strong winds. Wave-cut platform: the flat rocky area left as a cliff retreats.
Nutrient cycle: the movement of nutrients between plants, soil and litter in an ecosystem. Conflict: disagreement between groups who want to use the coast differently.
Erosion: waves wearing away rock along the coast.
Transportation: the movement of material along the coast. Suspension: fine material carried in the water.
Deposition: waves lose energy and drop the material they carry.
Mass movement: rock and soil moving down the cliff under gravity.
Hard engineering: built structures such as a sea wall. Soft engineering: working with nature, such as sand dune protection.
Storm surge: a rise in sea level caused by low pressure and strong winds. Wave-cut platform: the flat rocky area left as a cliff retreats.
Nutrient cycle: the movement of nutrients between plants, soil and litter in an ecosystem. Conflict: disagreement between groups who want to use the coast differently.
Constructive and destructive waves
Constructive waves: strong swash and weak backwash; low and further apart. The swash brings sediment up the beach and the backwash is too weak to remove it, so the beach builds up.
Destructive waves: weak swash and strong backwash; steep and close together. The backwash removes sediment, so they cause coastal erosion.
Destructive waves: weak swash and strong backwash; steep and close together. The backwash removes sediment, so they cause coastal erosion.
| Constructive | Destructive | |
|---|---|---|
| Swash | Strong | Weak |
| Backwash | Weak | Strong |
| Shape | Low, far apart | Steep, close together |
| Effect | Builds beaches | Erodes the coast |
The four types of erosion
Hydraulic action: waves force air into cracks; the air is compressed, then expands quickly as the wave retreats, like a small explosion, weakening the cliff.
Abrasion: waves throw rocks and pebbles at the cliff, grinding it like sandpaper. Abrasion is also called corrasion.
Attrition: rocks carried by the sea knock against each other and become smaller and more rounded.
Solution: weak acids in seawater dissolve rocks such as chalk and limestone. Solution is also called corrosion (note: corrasion means abrasion, not solution).
Coasts erode faster where the rock is soft or cracked, waves are big (long fetch, storms), there is no protective beach, and people have removed sand or built defences that move erosion along the coast.
Abrasion: waves throw rocks and pebbles at the cliff, grinding it like sandpaper. Abrasion is also called corrasion.
Attrition: rocks carried by the sea knock against each other and become smaller and more rounded.
Solution: weak acids in seawater dissolve rocks such as chalk and limestone. Solution is also called corrosion (note: corrasion means abrasion, not solution).
Coasts erode faster where the rock is soft or cracked, waves are big (long fetch, storms), there is no protective beach, and people have removed sand or built defences that move erosion along the coast.
Explained step by step
The hardest idea here is why one wave builds a beach and another destroys it. It all depends on swash (water rushing up the beach) and backwash (water draining back down).
A constructive wave is low and the waves are further apart. Its swash is strong, so it carries sand and pebbles up the beach. The backwash is weak because the water soaks into the beach and loses energy, so it cannot drag the material back. Result: the beach builds up.
A destructive wave is steep and the waves are close together. Its backwash is strong, so it drags sediment off the beach and out to sea. With the beach removed, waves can attack the cliff behind it. Result: coastal erosion.
Example: on a calm summer day you might see gentle constructive waves; in a winter storm, steep, frequent destructive waves remove sand and batter the cliffs.
A constructive wave is low and the waves are further apart. Its swash is strong, so it carries sand and pebbles up the beach. The backwash is weak because the water soaks into the beach and loses energy, so it cannot drag the material back. Result: the beach builds up.
A destructive wave is steep and the waves are close together. Its backwash is strong, so it drags sediment off the beach and out to sea. With the beach removed, waves can attack the cliff behind it. Result: coastal erosion.
Example: on a calm summer day you might see gentle constructive waves; in a winter storm, steep, frequent destructive waves remove sand and batter the cliffs.
Common mistakes and exam tips
Mixing up corrasion and corrosion: corrasion is abrasion (rocks thrown at the cliff); corrosion is solution (dissolving).
Saying destructive waves have a strong swash: it is the strong backwash that removes sediment.
Confusing abrasion and attrition: abrasion wears the cliff; attrition is rocks hitting each other and becoming smaller and rounder.
Mixing up weathering and erosion: weathering breaks rock down in place; erosion is waves wearing rock away.
Vague hydraulic action answers: say air is compressed in cracks and expands as the wave retreats, like a small explosion.
Saying destructive waves have a strong swash: it is the strong backwash that removes sediment.
Confusing abrasion and attrition: abrasion wears the cliff; attrition is rocks hitting each other and becoming smaller and rounder.
Mixing up weathering and erosion: weathering breaks rock down in place; erosion is waves wearing rock away.
Vague hydraulic action answers: say air is compressed in cracks and expands as the wave retreats, like a small explosion.
Waves and beach shape (from the class diagrams)
Your class wave diagrams add two details.
Constructive waves have a lower wave frequency (fewer waves per minute). The strong swash carries sediment up the beach and the weak backwash takes time to remove it, so they form a wide, gently sloping beach.
Destructive waves are high energy. The weak swash brings little material, but the strong backwash quickly removes sand, so they form a steep beach.
Sea or land? Your matching task splits the five processes: erosion, transportation and deposition happen in the sea, while weathering and mass movement happen on the land and affect the coast from above.
A coastline is constantly changing because of physical processes and the impact of human activities.
Constructive waves have a lower wave frequency (fewer waves per minute). The strong swash carries sediment up the beach and the weak backwash takes time to remove it, so they form a wide, gently sloping beach.
Destructive waves are high energy. The weak swash brings little material, but the strong backwash quickly removes sand, so they form a steep beach.
Sea or land? Your matching task splits the five processes: erosion, transportation and deposition happen in the sea, while weathering and mass movement happen on the land and affect the coast from above.
A coastline is constantly changing because of physical processes and the impact of human activities.
Spotting erosion, and famous coastlines
Your Expert activity asked what evidence of each erosion process you would see at the coast:
Hydraulic action: widened cracks and joints in the cliff, loosened blocks.
Abrasion: a smoothed, scraped cliff base, often with a notch and pebbles piled at its foot.
Attrition: small, smooth, rounded pebbles and sand on the beach.
Solution: pitted, dissolved surfaces on chalk or limestone.
Famous coastlines: the arch on your 'New Topic: Coasts' slide appears to be Durdle Door, a limestone arch on the Jurassic Coast in Dorset, UK. The white cliffs on the Expert slide look like Étretat in Normandy, France, famous for chalk cliffs with arches and a tall stack.
Your TIF task: for any famous coastline, record its location, two facts, two reasons people visit (scenery, beaches, walking) and two hazards (erosion, rockfalls, storm surges, flooding).
Hydraulic action: widened cracks and joints in the cliff, loosened blocks.
Abrasion: a smoothed, scraped cliff base, often with a notch and pebbles piled at its foot.
Attrition: small, smooth, rounded pebbles and sand on the beach.
Solution: pitted, dissolved surfaces on chalk or limestone.
Famous coastlines: the arch on your 'New Topic: Coasts' slide appears to be Durdle Door, a limestone arch on the Jurassic Coast in Dorset, UK. The white cliffs on the Expert slide look like Étretat in Normandy, France, famous for chalk cliffs with arches and a tall stack.
Your TIF task: for any famous coastline, record its location, two facts, two reasons people visit (scenery, beaches, walking) and two hazards (erosion, rockfalls, storm surges, flooding).
Explain how hydraulic action erodes a cliff.
- A wave hits the cliff and forces water and air into a crack.
- The air is compressed; when the wave retreats it expands rapidly, like a small explosion.
- Repeated over and over, this widens the crack and breaks pieces off the cliff.
Answer: Compressed air in cracks expands repeatedly, widening them.
A coastline is where land meets sea. Constructive waves (strong swash, low, far apart) build beaches; destructive waves (strong backwash, steep, close together) erode. Erosion: hydraulic action, abrasion (corrasion), attrition, solution (corrosion). Learn the key words: weathering, erosion, transportation, deposition, mass movement, hard and soft engineering, storm surge, wave-cut platform.
- Hydraulic action
- Erosion where the force of water, and air forced into cracks, breaks rock apart.
- Abrasion
- Erosion where rocks carried by waves, rivers or ice scrape and wear away the land.
- Attrition
- Erosion where rocks knock into each other and become smaller and rounder.
- Solution
- Erosion where water dissolves rocks such as chalk and limestone; also transport of dissolved minerals.
- Mass movement
- The downhill movement of rock or soil under gravity, such as sliding and slumping.
- Soft engineering
- Working with natural processes to manage a problem, such as beach nourishment or floodplain zoning.
All GCSE and International GCSE Geography A key terms and definitions →
- Not “Weak swash, strong backwash, steep and close together”. That describes a destructive wave.
- Not “Corrosion”. Corrosion is another name for solution.
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2 more questions
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Which describes a destructive wave?
- Strong swash, weak backwash, low and far apart
- Weak swash, strong backwash, steep and close together
- Strong swash and strong backwash, low and gentle
- Weak swash and weak backwash, far apart
Show the answer
Answer: Weak swash, strong backwash, steep and close together
Destructive waves are steep and close together, with a strong backwash that erodes.
How do destructive waves make a beach smaller?
- Their strong swash carries sediment onto the beach
- They are low and far apart
- They dissolve all the sand
- Their strong backwash drags sediment off the beach
Show the answer
Answer: Their strong backwash drags sediment off the beach
The strong backwash removes sediment from the beach.
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Checked by the GCSE-ready editorial team, 23 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.