Coastal Landforms & Processes
A Coast Is a Conveyor Belt
UK coasts look fixed but they are constantly moving. Waves, weather and gravity break rock from cliffs, longshore drift carries the pieces along the shore, and beaches and spits build where the energy drops. The same trio — erosion, transport and deposition — that shapes rivers also shapes coasts. The difference is that the energy comes from waves, tides and wind rather than gradient and discharge.
Coasts erode in four main ways: hydraulic action (water force compresses air in cracks), abrasion (sand and pebbles scrape the cliff), attrition (load knocks together and rounds), and solution (slightly acidic seawater dissolves rock).
Cliffs and Wave-Cut Platforms
A cliff forms where waves attack the base of the land. Hydraulic action and abrasion concentrate at the high-tide line, gradually carving a wave-cut notch. As the notch deepens the unsupported rock above collapses and the cliff retreats inland. The flat, gently sloping surface left behind is a wave-cut platform, often visible at low tide on the Yorkshire and Dorset coasts.
Where bands of hard and soft rock meet the sea at right angles, soft rock erodes faster and bays form between resistant headlands. Waves then concentrate their energy on the headlands. Cracks widen into caves, caves on opposite sides of a headland may break through to form an arch, and an unsupported arch eventually collapses to leave a stack standing offshore. Old Harry Rocks at the eastern end of Dorset shows the full sequence in chalk.
Transport Along the Coast
Sand and shingle do not stay where they fall. Most UK coasts have a prevailing wind that pushes waves up the beach at an angle. The water rushes back down the slope under gravity at right angles. The result is a zig-zag movement called longshore drift. Pebbles travel hundreds of metres a year, pushing material steadily along the coast. Wooden groynes — the low fences that cross many seaside beaches — are placed to slow this movement and trap sand for tourists.
Beaches, Spits and Bars
Where waves lose energy — usually in the lee of headlands or in sheltered bays — they drop their load. The result is a beach. Sandy beaches form in low-energy bays where fine grains can settle; pebble beaches form in higher-energy areas where only larger material can resist being moved away.
A spit is a long, narrow ridge of sand or shingle that grows from the coast across a bay or estuary. It forms where longshore drift continues past a sudden change in the coastline. The end often curves landward as a recurve, and salt marsh forms in the sheltered water behind.
Spurn Head, on the Yorkshire side of the Humber estuary, is a 5 km long spit built by longshore drift down the East Yorkshire coast. Sand and shingle from eroding boulder clay cliffs at Holderness travel south, then the coastline turns west into the Humber and the material is deposited as a curving ridge. Behind the spit, sheltered mudflats and salt marshes provide a feeding ground for migrating birds. Where a spit grows right across a bay, it becomes a bar, and a freshwater lagoon may form behind it — Slapton Ley in Devon is a UK example.
Look closely at a wave-cut platform and you will see smaller features. Rock pools form where pockets of softer rock are eroded out and trap seawater at low tide. Wave-cut notches mark the level where waves currently focus their energy on the cliff. Bedding planes — the lines between layers of rock — are picked out by erosion because waves attack the weaker layers first. These details show the same processes acting at different scales, from a single rock pool up to a whole bay.
Why the Pattern Matters
Coastal landforms cluster in predictable places. Headlands and stacks dominate where rock is hard or where bands of rock meet the sea at right angles. Beaches and spits dominate where energy drops — in bays, behind headlands, or where the coast bends sharply. Knowing the rule lets a geographer read a coastline: looking at a 1:50,000 OS map of Swanage Bay or Studland in Dorset, you can predict where erosion will dominate (the headlands) and where deposition will (the bay between).
Energy and Time
Coastal change does not happen evenly. Most erosion happens during a few stormy days each winter when waves are powerful and high tide arrives at the cliff base. In quiet summer weather, the same coast can be still for weeks. Add up the storms over decades and the cliff steadily retreats — sometimes losing a metre or more in a single year along boulder clay coasts like Holderness.