Coastal Processes & Landforms

The Coast as a System

A coastline is a working system. Energy from waves, wind and tides arrives at the shore and reshapes it constantly. The geographer’s job is to track where the energy comes from, what it does to the rock and sediment, and where the material ends up. Three families of process do almost all the work: weathering, erosion, and deposition. Between erosion and deposition sits transport, which simply moves sediment from one place to another.

Waves: Constructive and Destructive

Waves are the engine of the coast. Constructive waves are low and long. Their swash (the rush up the beach) is strong, while the backwash is weak, so they push sediment up the beach and build it up. Destructive waves are tall and steep. Their backwash is stronger than their swash, so they drag sediment back out to sea and tear into cliffs. The UK’s storm-prone west coast sees more destructive waves; sheltered east-coast bays see more constructive ones.

How Sediment Travels

Once eroded, material has to go somewhere. Four transport processes carry it along. Traction rolls heavy pebbles along the seabed; saltation bounces smaller pebbles in short hops; suspension carries fine sand and silt within the water; and solution dissolves chemicals like calcium carbonate that travel invisibly. Most importantly, longshore drift moves sediment along the coast in the direction of the prevailing wind. Waves push sand up the beach at an angle (swash) but pull it straight back down (backwash), so each grain shifts slightly along the coast every cycle.

Erosional Landforms: Headlands, Bays, Cliffs & Stacks

Where bands of hard and soft rock meet the sea at right angles, the soft rock erodes faster, leaving the hard rock sticking out as a headland with bays between. The Dorset coast at Swanage shows this perfectly: chalk and limestone form headlands; soft clay forms the bays.

On a single headland, weaknesses in the rock evolve into a sequence: a small crack widens into a cave; two caves on opposite sides of a headland meet to form an arch; the arch’s roof eventually collapses, leaving a stack isolated in the sea; the stack is undercut and falls, becoming a shorter stump. The Old Harry Rocks on the Jurassic Coast and the stacks at Flamborough Head are textbook examples. Cliffs themselves retreat by the same processes: undercutting at the wave-cut notch causes the rock above to collapse, leaving a flat wave-cut platform.

Depositional Landforms: Beaches, Spits & Bars

Where waves lose energy — in sheltered bays, behind headlands, or where the coast suddenly changes direction — sediment piles up. Beaches form between the high and low tide marks. Sandy beaches are gentle (low-energy waves); pebble beaches are steeper (higher-energy storms). A spit forms where longshore drift carries sediment beyond a sudden bend in the coast and deposits it into open water; the end of the spit often hooks back, sheltering a salt marsh behind it. Spurn Head on the Yorkshire coast is a classic UK spit. A bar forms when a spit grows all the way across a bay, trapping a lagoon behind it.