Key Terms

📖 Key Terms

Fetch

The distance of open water over which wind has been blowing before it reaches the coast. The longer the fetch, the more energy waves carry when they arrive. The Atlantic coast of the UK has a fetch of over 3,000 km; the English Channel coast has a fetch of a few hundred kilometres.

Swash

The rush of water up the beach after a wave breaks. In constructive waves, swash is dominant — it pushes sediment up the beach and deposits it there.

Backwash

The flow of water back down the beach under gravity after swash. In destructive waves, backwash is dominant — it pulls sediment back down the beach and out to sea.

Constructive wave

A low, long wave with strong swash and weak backwash that deposits sediment on the beach. Frequency: 6–8 waves per minute. Builds up beaches and depositional landforms.

Destructive wave

A tall, steep wave with strong backwash and weak swash that removes sediment from the beach and erodes the cliff. Frequency: 10–14 waves per minute. Dominant in stormy, high-fetch conditions.

Hydraulic action

Erosion caused when waves trap and compress air in cracks in a cliff face. When the wave retreats, the sudden pressure release forces the crack walls apart. The most effective process at attacking joints and fractures.

Abrasion (corrasion)

Erosion caused when waves hurl sediment (sand, pebbles, boulders) against the cliff face, wearing it down like sandpaper. Most effective at the base of cliffs where wave energy concentrates.

Solution (corrosion)

Chemical erosion where slightly acidic seawater dissolves calcium carbonate in limestone and chalk rocks. No mechanical force needed — the rock is chemically dissolved.

Attrition

The wearing down of sediment particles as they collide with each other and the seabed during transportation. Angular boulders become rounded pebbles, which become sand. Explains why sediment gets finer downdrift.

Longshore drift

The zigzag movement of sediment along the coast. Swash carries sediment up the beach at the angle of the prevailing wind; backwash pulls it straight back down under gravity. Net movement is in the direction of the prevailing wind.

Wave-cut notch

A horizontal groove eroded at the base of a cliff at the high-tide waterline, cut by hydraulic action and abrasion. When it deepens enough, the cliff above becomes unsupported and collapses.

Wave-cut platform

The flat or gently sloping rock surface exposed at low tide in front of a cliff, left behind as the cliff retreats. Its width indicates the extent of cliff retreat over thousands of years.

Spit

A narrow ridge of sand or shingle extending from the land into the sea at a change in the direction of the coastline. Formed by longshore drift. Often has a curved tip caused by wave refraction.

Sediment budget

The balance between the amount of sediment being added to and removed from a section of coast. Coastal management that prevents erosion upstream reduces the sediment supply to beaches and spits further down the coast.