Coastal Landscapes of Erosion & Deposition

A Coast Made by Waves and Rock

The UK has roughly 31,000 km of coastline. Stand at Lulworth Cove on a winter morning and you can hear waves smashing against the chalk cliffs, sending vibrations through your boots. The sea is a slow but relentless engineer. Combined with the rocks it works on and the weather above, it carves cliffs, hollows out caves, and builds new beaches and spits from the broken material it carries away. To explain any UK coastal landscape you need three ingredients: geology, marine processes (waves and tides), and sub-aerial processes.

Two Types of Wave

Waves are the engine of the coast. Destructive waves are tall, steep and frequent (10–14 per minute). Their swash is weak compared with their backwash, so they pull material off the beach and into the sea. They erode cliffs. Constructive waves are long, low and less frequent (6–9 per minute). Their swash is strong, their backwash weak, so they push material up the beach. They build beaches and spits. The same coastline can shift between the two depending on storms and seasons.

Coastal Erosion: Four Processes

Destructive waves erode rocks in four ways. Hydraulic action — air trapped in cracks is compressed by waves and explodes outwards as the wave retreats, breaking the rock. Abrasion — waves throw sand and pebbles against the cliff like sandpaper. Attrition — rocks already in the water are knocked against each other, becoming rounder and smaller. Solution (or corrosion) — sea water dissolves soluble rock such as chalk and limestone. These four processes work together over thousands of years to grind cliffs back.

Geology Shapes the Coast

Where alternating bands of hard and soft rock meet the coast at right angles — a discordant coastline — the soft rock is eroded faster, leaving the hard rock as headlands sticking out into the sea, with bays in between. The Dorset coast at Studland Bay (chalk headlands, sandy clay bay) is the classic UK example. Where the rock bands run parallel to the coast — a concordant coastline — the front layer protects what is behind it, creating long, straight cliffs broken only where waves punch through. Lulworth Cove formed when the sea breached a hard limestone band and then carved a circular bay out of the soft sands behind.

Sub-Aerial Processes and Cliff Retreat

Cliffs are not only attacked from the sea. From above, weathering — especially freeze-thaw in winter — opens cracks. After heavy rain, mass movement drags loose material down the cliff face. The Holderness coast in East Yorkshire, made of soft glacial till, retreats by about 2 metres a year on average — one of the fastest erosion rates in Europe. At least 30 villages have been lost to the sea since Roman times. Today, the road to the beach at Aldbrough stops at the cliff edge, and families at Skipsea have had to leave cliff-top homes.

Transport and Deposition

Material eroded from one part of the coast is moved along the shore by longshore drift. Waves usually approach the shore at an angle (set by the prevailing wind), so the swash carries pebbles diagonally up the beach. Gravity pulls the backwash straight down the slope, leaving the pebble slightly to the side. Repeated, this zigzags material along the coast, sometimes for tens of kilometres.

Where the coast changes direction, longshore drift continues out to sea, dropping its load and building a spit — a long ridge of sand and shingle. Spurn Head, the 5 km curved spit at the mouth of the Humber, is built from material eroded from the Holderness cliffs further north. Behind a spit, sheltered water silts up into a salt marsh. Beaches form wherever constructive waves dominate; bars form when a spit grows right across a bay.