Physical geography · GCSE Geography
Coasts
Waves, erosion, transport and deposition, the landforms they build, and why coastal management always creates winners and losers.
Waves do four jobs: smash, scrape, knock stones together, dissolve.
The important bits
What you need to know
- 1
Destructive waves are high-frequency, high-energy, with a strong backwash that erodes. Constructive waves are lower-frequency, with a strong swash that deposits. Wave type is the first control on a stretch of coast.
- 2
Erosion processes: hydraulic action (air compressed in cracks), abrasion/corrasion (sediment as sandpaper), attrition (pebbles smash each other smoother), solution/corrosion (chemical weathering of lime-rich rock).
- 3
Transport: traction, saltation, suspension, solution. Longshore drift moves sediment along the beach in the direction of the prevailing swash; groynes exist to interrupt that conveyor.
- 4
Erosional landforms: headlands and bays (discordant coasts), wave-cut notches and platforms, the cave–arch–stack–stump sequence on headlands (Old Harry, Durdle Door). Learn the sequence as a cartoon you can annotate.
- 5
Depositional landforms: beaches, spits (Spurn Head off Holderness), bars, tombolos, salt marsh in the sheltered lee. Spits need a sudden change in coastline direction and a supply of sediment from LSD.
- 6
Holderness is a classic fast-eroding UK coastline: glacial till, strong waves, villages lost (Skipsea, former Dropping Well). Mappleton’s rock groynes protected one place and starved sediment down-drift — the political geography of coasts.
- 7
Hard engineering (sea walls, groynes, rock armour, gabions) is expensive, obvious and often shifts erosion along the coast. Soft engineering (beach nourishment, dune regeneration) works with processes. Managed retreat (Medmerry, Sussex) lets the sea in on purpose.
- 8
Management is a cost–benefit and fairness problem: whose houses, whose nature reserve, whose council tax. SMP (Shoreline Management Plan) options — hold the line, advance, managed realignment, no active intervention — are the language of 9-markers.
Go deeper
The stack sequence, without missing a step
Waves attack a line of weakness (joint or fault) on a headland with hydraulic action and abrasion. The crack widens into a cave. If caves back into each other from opposite sides, or a cave breaks through, an arch forms. Weathering and gravity collapse the arch roof; a stack stands detached (Old Harry). Basal erosion and weathering reduce it to a stump, covered at high tide. A wave-cut platform often fringes the whole story as the cliff line retreats. Examiners punish missing steps or putting deposition in the middle. They also like a named rock type: chalk at Old Harry is well jointed and chemically vulnerable, so the sequence runs quickly in geological terms.
Go deeper
Why groynes create enemies next door
Longshore drift is a conveyor. A groyne traps sand on its up-drift side, widening the beach so waves break earlier and lose energy — good for that village’s cafes and cliffs. Down-drift, the beach starves, waves hit the cliff harder, and erosion accelerates. Mappleton on the Holderness coast is the standard unhappy neighbour story after 1991 rock groynes. This is why “just build groynes” is a weak 6-mark answer. Sustainable coastal management has to think in sediment cells, not parish boundaries. Sometimes the honest option is to stop defending farmland and let a salt marsh take the wave energy inland.
See the idea in action
Question: explain the formation of a spit. Prevailing waves approach at an angle; swash carries sediment up the beach; backwash pulls it down the steepest slope; net movement is alongshore (LSD). Where the coast bends (estuary mouth), sediment continues in the old direction into open water, building a ridge. The end hooks if wind/wave direction changes. Salt marsh may form in the calm behind. Locate it: Spurn Head at the Humber, fed by Holderness erosion.
Exam technique
Turn knowledge into marks
Draw. A 4-mark landform question is often won by a simple sequence sketch with three labels. Practise Old Harry and Spurn until you can do them in sixty seconds.
Common mistakes
Do not give these marks away
- 01
Putting hydraulic action, abrasion, attrition and solution in the wrong jobs, or calling them all “erosion” without a process.
- 02
Forming a spit with no longshore drift and no change in coastline direction.
- 03
Assuming hard engineering is always “better”. It is often locally effective and regionally unfair.
How does a spit form?
ADestructive waves cut a cave through a headland
BLongshore drift carries sediment past a bend in the coast and deposits it in open water
CA river dumps alluvium at a waterfall
DGlaciers push moraine into the sea
Show the answer
Longshore drift carries sediment past a bend in the coast and deposits it in open water. When the coastline changes direction, the conveyor of sand and shingle continues, building a ridge into the sea. The hook and the salt marsh are extras; LSD plus a bend is the engine.
Quick questions
If this is the bit you searched
What is the difference between erosion and weathering on a cliff?
Erosion is wearing by waves (and the sediment they carry). Weathering is breakdown in place by rain, freeze–thaw, salt and plants. They work together: weathered rock is easier for waves to remove.
Is managed retreat just giving up?
It is a planned realignment: breach a low-value defence, create intertidal habitat that absorbs energy, and stop pouring money into unsustainable hold-the-line. It is politically hard because someone still loses land.