Coastal Erosion

Coastal erosion is the wearing away of the land by the sea. Waves use hydraulic action, abrasion, attrition, and solution to gradually break down cliffs, headlands, and beaches, reshaping coastlines over time.

What Is Coastal Erosion?

Coastal erosion is the process by which the sea wears away the land at the coast. Waves carry enormous energy and use it to break down and remove rock and sediment from the coastline. Coastal erosion creates dramatic landforms like sea cliffs, sea caves, arches, and stacks.

Coastal erosion can threaten homes and infrastructure built near cliffs, and managing it is a major challenge for coastal communities.

Waves and Their Energy

Waves are created by wind blowing over the ocean surface. The longer the distance of open water over which wind blows (the fetch), the larger and more powerful the waves.

Destructive waves: Powerful, with a strong swash and weak backwash. They crash onto the coast with force and create erosion. Common on high-energy, exposed coasts.

Constructive waves: Weaker, with a strong backwash and gentle swash. They deposit more material than they erode. Common on sheltered, low-energy coasts.

Note

The coast of Cornwall in southwest England faces the full fetch of the Atlantic Ocean — waves can travel thousands of kilometres from America without hitting any land, building up enormous energy. This is why the Cornish coast has dramatic cliffs and is popular with surfers. The east coast of England, sheltered and with less fetch, has more beaches and less dramatic cliffs.

Processes of Coastal Erosion

1. Hydraulic action: The force of waves crashing against cliffs compresses air in cracks. When the wave retreats, the trapped air expands like a mini explosion, widening cracks and breaking off pieces of rock.

2. Abrasion (corrasion): Waves throw sand, pebbles, and boulders at the cliff face, grinding it away like sandpaper.

3. Attrition: Rocks and pebbles in the water collide with each other, breaking and rounding into smaller, smoother pieces over time.

4. Solution (corrosion): Slightly acidic seawater dissolves certain rocks, especially limestone and chalk, removing material chemically.

Coastal Erosion Features

The combination of these processes creates recognisable coastal landforms:

Wave-cut notch: Erosion near the waterline undercuts the cliff, forming a notch. Wave-cut platform: As the cliff retreats, a flat, rocky platform is left at its base. Sea cave: A crack in the cliff face is enlarged by hydraulic action into a cave. Sea arch: Two caves erode from opposite sides of a headland until they meet, forming an arch. Sea stack: An arch collapses, leaving an isolated pillar of rock in the sea. Sea stump: A stack erodes further, leaving a low, flat rock.

Tip

The Old Man of Hoy (Orkney, Scotland) is a famous 137-m high sea stack. It formed after wave erosion broke through a headland to form an arch, which later collapsed, leaving the isolated pillar. The original stack is relatively young — estimated to be only a few hundred years old — and will eventually collapse into the sea too.

Real world: Holderness Coast — fastest eroding in Europe

The Holderness Coast in Yorkshire, England, is one of the fastest-eroding coastlines in Europe — losing up to 2 metres of land per year. The cliffs are made of soft boulder clay deposited by glaciers during the last Ice Age. Entire villages have fallen into the sea over the past millennium. Today, the few towns with hard sea defences are protected, but the stretches in between are left to erode "naturally" — a policy called "managed retreat" — meaning farms and homes continue to be lost.

Real world: The Cornish coast and Atlantic fetch

Cornwall in southwest England faces the full fetch of the Atlantic Ocean — waves can travel uninterrupted from the coast of North America, building to enormous heights and power. This creates spectacular cliffs, sea caves, arches, and stacks at places like Land's End. The same powerful waves that create dramatic scenery also make the Cornish coast a world-famous destination for surfers — wave heights regularly exceed 4–5 metres in winter.

Real world: Coastal defence and the Maldives

The Maldives — a chain of low-lying islands in the Indian Ocean — face an existential threat from coastal erosion and rising sea levels. The highest point on the Maldives is only 2.4 m above sea level. The government has spent hundreds of millions of dollars on artificial sea walls, coral reef protection, and island land reclamation. Some islands have already been abandoned. The Maldives is one of the world's most dramatic examples of coastal erosion as a national security issue.

Tip

Where do you see this in real life? When storms hit the news in winter and you see images of waves crashing over sea walls and flooding coastal streets — that is coastal erosion and destructive wave energy happening in real time.

Practice Problems

Explain how a sea arch forms from a headland.

Show answer

First, waves exploit weaknesses (cracks and joints) in the headland rock, using hydraulic action and abrasion to enlarge them into sea caves on both sides of the headland. As erosion continues, the caves deepen. Eventually the two caves from opposite sides of the headland meet and break through, forming a natural arch of rock. The arch is then further eroded at its base until the roof becomes too thin and collapses.

Why is a coast with a long fetch more vulnerable to wave erosion than a sheltered coast?

Show answer

Fetch is the distance of open water over which wind blows to create waves. A longer fetch allows waves to travel further and build up more energy. The waves arriving at a coast with long fetch are therefore much more powerful (destructive waves) and carry more energy to erode cliffs and headlands. A sheltered coast has a short fetch — weaker waves with less energy that tend to deposit rather than erode.