Coastal Processes and Landforms

Waves — The Driver of Coastal Change

Waves are created by wind blowing across the surface of the sea. The fetch is the distance over which the wind blows — a longer fetch creates larger, more powerful waves. The UK's west coast faces the Atlantic Ocean (very long fetch → powerful, destructive waves); the east coast faces the North Sea (shorter fetch → less powerful on average).

Constructive waves (gentle gradient, long wavelength):

• Strong swash (water moving up the beach), weak backwash
• Build up beaches; found in sheltered bays

Destructive waves (steep gradient, short wavelength):

• Weak swash, strong backwash
• Erode coastlines; found on exposed coasts

Coastal Erosion Processes

The same four erosion processes as rivers apply:

1. Hydraulic action: waves trap and compress air in cracks — the pressure erodes rock
2. Abrasion: waves hurl rock particles at the cliff face — sandpaper effect
3. Attrition: particles carried by waves knock against each other → smaller, rounder
4. Solution/corrosion: seawater dissolves carbonate rocks (limestone, chalk)

Mass Movement at the Coast

Landslides: Saturated cliff material slides along a failure plane (e.g., Holbeck Hall Hotel, Scarborough, 1993) Rockfall: Individual rocks break off from cliff face (most common in hard-rock coasts) Slumping: Rotational movement of saturated material — common in clay and boulder clay cliffs

Coastal Landforms

Headlands and Bays

• Formed where hard and soft rock bands alternate at the coast
• Soft rock erodes faster → bays; hard rock resists → headlands
• Example: Swanage Bay (Jurassic Coast, Dorset) — chalk and limestone headlands flanking softer clay bays

Cliffs, Notches and Wave-Cut Platforms

1. Waves attack the cliff base at the waterline (hydraulic action, abrasion)
2. A wave-cut notch is carved at the base
3. The cliff above becomes unsupported and collapses
4. The cliff retreats; the flat rock surface at the base is the wave-cut platform

Caves, Arches and Stacks

1. Cave: hydraulic action exploits a weakness/crack in the headland
2. Arch: caves on opposite sides of the headland break through → arch
3. Stack: roof of the arch collapses → isolated pillar of rock (stack)
4. Stump: stack collapses to a low stump

Example: Old Harry Rocks (Dorset) — chalk stacks; Durdle Door (Dorset) — limestone arch

Beaches

• Formed by the deposition of sand and shingle (constructive waves)
• Sandy beaches: gentle, shallow gradient; shingle beaches: steeper gradient
• Longshore drift moves sediment along the coast in the direction of prevailing wind

Spits

• Form where longshore drift continues around a change in the coastline (e.g., an estuary mouth)
• Sediment builds up in the same direction as drift
• The tip may curve due to secondary winds → a recurved spit
• Example: Spurn Point (Humber Estuary); Blakeney Point (Norfolk)

Longshore Drift — Key Process

Waves approach the beach at an angle (from prevailing wind direction). Swash carries sediment up the beach at this angle; backwash carries it straight back down (by gravity). Net movement is along the coast in the direction of the prevailing wind.