Watch the sea crash against a cliff and you are watching a slow war between water and rock. Every wave chips a little more away; every calm day quietly builds a beach. Britain has over 12,000 kilometres of coastline, and no two stretches look the same — towering chalk cliffs, curving sandy bays, long fingers of shingle reaching into the sea. All of it is shaped by waves.
Two kinds of wave
| Constructive waves | Destructive waves |
|---|---|
| Low, gentle, far apart | Tall, powerful, close together |
| Strong swash builds up the beach | Strong backwash drags the beach away |
| Deposit sand and shingle | Erode the coastline |
The swash is the water rushing up the beach; the backwash is the water draining back. Constructive waves have a strong swash (they build); destructive waves have a strong backwash (they destroy).
Erosion and its landforms
The same four processes as rivers erode the coast: hydraulic action, abrasion, attrition and solution. Where a coast has hard and soft rock, the soft rock erodes into bays and the hard rock is left sticking out as headlands.
- Cave: waves erode a weakness into a hollow.
- Arch: the cave is cut right through the headland.
- Stack: the arch roof collapses, leaving a pillar of rock.
- Stump: the stack is worn down to a stub.
Deposition and its landforms
Where waves lose energy they drop their load, building beaches. Longshore drift moves material along the coast in a zig-zag: swash pushes it up the beach at an angle, backwash drags it straight back down. Where the coastline turns, the material keeps going and builds a spit — a long finger of sand or shingle reaching out to sea, often with a curved (recurved) end.
Managing the coast
| Method | What it does |
|---|---|
| Sea wall | Hard barrier that reflects wave energy (expensive) |
| Groynes | Wooden fences that trap sand and slow longshore drift |
| Beach nourishment | Adding new sand to widen the beach |
| Managed retreat | Letting the sea flood low-value land instead of defending it |