Coastal landscapes · GCSE Geography

Waves and weathering

Waves are made by wind blowing over the sea. Constructive waves are low and gentle, with a strong swash and a weak backwash, so they build up beaches. Destructive waves are high and steep, with a weak swash and a strong backwash, so they remove material.
Weathering breaks down rock where it is: mechanical (freeze–thaw), chemical (e.g. rainwater slowly dissolving chalk and limestone) and biological (e.g. plant roots).
Mass movement is rock and soil moving downhill under gravity: sliding, slumping (a curved, rotational slip, common in clay cliffs) and rock falls.

Erosion: hydraulic power (waves force air into cracks), abrasion (waves throw rocks at the cliff), attrition (rocks knock together and become smaller and rounder) and solution (rock dissolves).
Transportation: traction (large boulders roll), saltation (pebbles bounce), suspension (fine material is carried in the water) and solution (dissolved material).
Longshore drift: the prevailing wind drives waves onto the beach at an angle. The swash carries material up the beach at that angle, and the backwash pulls it straight back down, so material zigzags along the coast.
Deposition happens where the water loses energy, such as in sheltered bays.

Headlands and bays form where bands of hard and soft rock meet the sea: the soft rock erodes back into bays, leaving the hard rock sticking out as headlands.
Cliffs retreat as waves undercut them, leaving a wave-cut platform. A crack in a headland is eroded into a cave, then an arch; when the arch collapses, a stack is left, which erodes into a stump. Examples: Old Harry, a chalk stack near Swanage in Dorset, and Durdle Door, an arch.
Deposition forms beaches, sand dunes, spits and bars. A spit is a ridge of sand or shingle that grows out from the coast where it changes direction, such as Spurn Head at the mouth of the Humber. A bar is a spit that grows across a bay, trapping a lagoon behind it.

Hard engineering: sea walls reflect waves but are expensive; groynes trap material moved by longshore drift, but can starve beaches further along; rock armour (large boulders) absorbs wave energy; gabions are cages filled with rocks.
Soft engineering: beach nourishment (adding sand or shingle) and reprofiling, and dune regeneration (planting marram grass and fencing).
Managed retreat: letting the sea flood low-value land, creating salt marsh that absorbs wave energy.
Example: the Holderness coast erodes by about 2 m a year, one of the fastest rates in Europe. At Mappleton, a £2 million scheme in 1991 built rock armour and two rock groynes. It protected the village and its coast road, but reduced the sediment moving south, so erosion increased further along the coast, such as at Cowden.

Constructive wave: A low, gentle wave with a strong swash that builds up beaches.
Destructive wave: A high, steep wave with a strong backwash that removes material.
Hydraulic power: Erosion by waves forcing air into cracks in the rock.
Abrasion: Erosion by rocks being thrown against the cliff.
Longshore drift: The movement of material along the coast by waves.
Wave-cut platform: A flat, rocky area left at the foot of a retreating cliff.
Stack: A pillar of rock left standing in the sea when an arch collapses.
Spit: A ridge of sand or shingle growing out from the coast into the sea.
Groyne: A barrier built out into the sea to trap material moved by longshore drift.
Managed retreat: Letting the sea flood an area of low-value land in a controlled way.