What Is Coastal Erosion? A KS3 Geography Guide

Coastal erosion is the wearing away and removal of rock, sediment and soil from a coastline by the action of waves, weather and the sea. It is a natural process that reshapes cliffs, beaches and headlands over time — but it is also accelerated by human activity and climate change, making it one of the most significant geographical hazards facing the UK's coastline.

What causes coastal erosion?

Coastal erosion is driven primarily by wave energy — the force that waves carry as they travel across open water and crash against the coast. The higher the waves and the more frequently they strike, the faster erosion occurs. Several factors influence how erosive a coast is:

Fetch — the distance over which wind has blown across open water to generate a wave. Longer fetch = bigger, more energetic waves. The south-west coast of England faces the full fetch of the Atlantic Ocean, which is why cliffs in Cornwall and Dorset are among the most actively eroded in the UK.

Rock type and structure — soft rocks such as clay and sand erode far faster than hard rocks such as granite and chalk.

Cliff angle — steep, near-vertical cliffs are exposed to maximum wave energy at their base.

Human activity — removing beach sediment, building sea walls, or altering drainage can all accelerate or change the pattern of erosion.

The four main processes of coastal erosion

KS3 geography students are expected to know and distinguish between four erosion processes.

1. Hydraulic action

Waves crash against a cliff face and compress air trapped in cracks in the rock. When the wave retreats, the air pressure is suddenly released, forcing the cracks to widen. Over time, repeated compression and decompression causes chunks of rock to break away. Hydraulic action is most powerful in storm conditions when waves are large and fast.

2. Abrasion (corrasion)

Waves pick up sand, pebbles and boulders and hurl them against the cliff face, wearing it away like sandpaper on wood. This is often the dominant process of erosion on rocky coastlines. Over many years, abrasion cuts a wave-cut notch at the base of a cliff, undermining it until the cliff above collapses.

3. Attrition

As rock fragments and boulders are transported by waves, they collide with each other and break into smaller, rounder, smoother pieces. Attrition does not erode the cliff itself — it is the process that creates the smooth pebbles you find on a beach. Larger angular rocks gradually become the smaller, rounded stones typical of shingle beaches.

4. Corrosion (solution)

Seawater is mildly acidic and can dissolve certain types of rock, particularly limestone and chalk. This chemical weathering is called corrosion or solution. It works slowly compared to the mechanical processes above, but over geological time it contributes significantly to cliff retreat.

How coastal erosion creates landforms

Erosion does not simply remove material — it sculpts distinctive landforms that are central to KS3 coastal geography.

Headlands and bays

Where a coastline contains alternating bands of hard and soft rock running perpendicular to the sea, the soft rock erodes faster to form bays, while the harder rock juts out as headlands. This differential erosion is visible across much of the Jurassic Coast in Dorset. Once a headland has formed, it concentrates wave energy on its sides.

Wave-cut platforms

Abrasion cuts a notch at the base of a cliff. As the cliff overhangs the notch, gravity causes it to collapse, retreating inland. The flat or gently sloping rock shelf left behind at the base of the cliff is called a wave-cut platform, visible at low tide along many UK coastlines.

Caves, arches and stacks

Hydraulic action and abrasion exploit weaknesses (cracks and joints) in headlands to form caves. When caves on opposite sides of a headland break through, they create an arch. Eventually the arch roof collapses, leaving an isolated column of rock called a stack. The most famous example in England is Old Harry Rocks in Dorset, where a stack (Old Harry), a stump (Old Harry's Wife), and an arch all appear within metres of each other — a textbook illustration of this sequence of landform development.

Coastal erosion in the UK: a real example

The Holderness Coast of East Yorkshire is the fastest-eroding coastline in Europe. According to the British Geological Survey, cliff retreat here averages around 1.5 to 2 metres per year, with some sections losing up to 10 metres in a single storm. The cliffs are made of soft glacial till (clays and sands deposited at the end of the last Ice Age), which offers little resistance to wave action. Since Roman times, an estimated 30 villages have been lost to the sea along this stretch of coast.

The village of Skipsea is a contemporary example: its clifftop is monitored by the Environment Agency and local councils, and some properties have had to be demolished as the cliff edge has approached. This makes Holderness a valuable case study for discussing the human and economic impacts of coastal erosion, and the difficult decisions communities face about whether to defend, retreat or adapt.

Frequently asked questions

What are the four types of coastal erosion?

The four main processes are: hydraulic action (wave pressure compressing and expanding air in rock cracks), abrasion (waves throwing sediment against the cliff face), attrition (eroded material breaking into smaller fragments as pieces collide), and corrosion (the chemical dissolving of rock, especially limestone, by mildly acidic seawater).

What is a wave-cut platform?

A wave-cut platform is a flat or gently sloping shelf of rock that is exposed at low tide at the base of a retreating cliff. It forms because abrasion cuts a notch at the cliff base; the overhanging cliff collapses; and the cycle repeats as the cliff retreats inland, leaving the eroded rock surface behind.

Why is the Holderness Coast eroding so quickly?

The Holderness Coast erodes rapidly because its cliffs are made of soft glacial till — loose clay and sand deposited by glaciers during the last Ice Age — which offers very little resistance to wave energy. The coast also faces a long fetch across the North Sea, which gives waves significant energy. Additionally, the longshore drift of sediment southwards means that material removed by erosion is carried away rather than redeposited locally to protect the cliff base.

How does coastal erosion affect people?

Coastal erosion can destroy homes, farmland, roads and historical sites. In the UK, thousands of properties are at risk from cliff retreat. Coastal communities must decide whether to invest in expensive sea defences (such as sea walls, rock armour or groynes), manage a controlled retreat by abandoning land to the sea, or allow natural processes to continue. Each option involves trade-offs between cost, environmental impact and the displacement of people and communities.

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