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Waves, beach profiles and marine erosion

Edexcel IAL Geography · WGE02 Geographical Investigations

Waves supply the energy that shapes coasts. Their type controls the shape of beaches, and erosion processes attack cliffs (spec 2.3.2, key idea 4).

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Constructive and destructive waves

Waves are created by wind blowing over the sea; their energy depends on wind speed, duration and fetch.

Constructive waves: low height, long wavelength, low frequency. Swash is stronger than backwash, so sediment is pushed up the beach. They build a gentle, wide beach with berms.
Destructive waves: high, short wavelength, high frequency. Backwash is stronger than swash, so sediment is dragged off the beach. They create a steep profile in the upper beach and move sediment offshore into bars.

	Constructive	Destructive
Height	Low	High
Wavelength	Long	Short
Swash vs backwash	Swash stronger	Backwash stronger
Effect on beach	Builds gentle beach, berms	Removes sediment, steep profile, offshore bars

Seasonal beach profiles

Beach profiles change with the seasons. In many places, winter storms bring destructive waves that cut the beach back and move sand offshore into bars, leaving a steeper, narrower beach. Summer constructive waves return the sand, building a wider beach with a berm. A shingle beach is usually steeper than a sand beach because water percolates into the large gaps, weakening backwash.

The June 2025 mark scheme credited: destructive waves have weak swash and strong backwash, removing sediment and creating a steep profile or an offshore bar.

Erosion processes

Hydraulic action: the force of water hitting the cliff and compressing air in cracks; when the wave retreats the air expands explosively, widening cracks.
Abrasion (corrasion): waves hurl sand and pebbles at the cliff, wearing it away like sandpaper.
Attrition: rocks carried by waves hit each other and become smaller and rounder.
Solution (corrosion): chemical dissolving of rock such as limestone by sea water.

Rock type and structure (strata, faults, joints) control how effective these processes are and so control cliff profiles and erosion rates. Note: the June 2025 mark scheme did not credit weathering or mass movement as erosion processes.

Worked example

A beach is surveyed in September and again in February. In February it is steeper and narrower, with a sand bar offshore. Explain the change.

Winter storms produced destructive waves (high, frequent).
Backwash was stronger than swash, so sand was dragged down the beach.
The sand was deposited offshore as a bar, leaving a steeper, narrower beach.

Answer: Destructive winter waves moved sand offshore.

Key idea: Constructive: swash > backwash, builds gentle beaches. Destructive: backwash > swash, steep profile, offshore bars. Erosion: hydraulic action, abrasion, attrition, solution.

Check yourself

Which feature describes a constructive wave?
- Backwash stronger than swash
- Swash stronger than backwash
- High frequency and great height
- Short wavelength and great height
Show answer
Swash stronger than backwash. Constructive waves push sediment up the beach.
Sand and pebbles thrown against a cliff by waves is
- attrition
- solution
- hydraulic action
- abrasion
Show answer
abrasion. Abrasion (corrasion) is the sandpaper effect.
Which process makes beach pebbles smaller and rounder over time?
- Abrasion
- Attrition
- Solution
- Freeze-thaw
Show answer
Attrition. Pebbles knock against each other.
Which of these would NOT be credited as a marine erosion process?
- Hydraulic action
- Abrasion
- Mass movement
- Solution
Show answer
Mass movement. Mass movement is a subaerial process, not wave erosion (June 2025 mark scheme).
In many places, beaches are narrower and steeper in winter because
- destructive storm waves remove sediment offshore
- constructive waves add more sand
- tides stop in winter
- sea level falls in winter
Show answer
destructive storm waves remove sediment offshore. Storm waves have strong backwash.
Explain how hydraulic action erodes a cliff.
Show answer
Waves force water and air into cracks in the cliff; the air is compressed and then expands explosively when the wave retreats, which widens the cracks until pieces break off.. Water and air in cracks, pressure, widening.

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Last updated 8 November 2026. Spotted a mistake? Tell us.