What Are Sea Cliffs?
Sea cliffs are steep, rocky faces that form where land meets the sea on high-energy coasts. They vary from a few metres to hundreds of metres in height. The White Cliffs of Dover (UK) are made of chalk and rise to about 107 m; the Cliffs of Moher (Ireland) are up to 214 m high.
Cliffs form where:
- The rock is resistant enough to support a steep face.
- Waves have enough energy to erode the base.
- The land is higher than sea level.
How Cliffs Form and Retreat
Cliffs are shaped by the process of wave undercutting:
- Waves erode the base of the coastal rock face using hydraulic action and abrasion.
- A wave-cut notch (a horizontal groove) forms at the waterline.
- As the notch deepens, the rock above it becomes unsupported and overhanging.
- Eventually, the overhanging rock collapses — the cliff retreats landward.
- The fallen material is broken up and carried away by waves.
- A wave-cut platform (a gently sloping, rocky ledge) is left at the base of the retreated cliff.
The chalk cliffs at Beachy Head (East Sussex, England) retreat by an average of 40–70 cm per year, though spectacular collapses can remove several metres in a single event. Chalk is relatively soft, and the cliffs are very high, so when undercutting has weakened the base, huge sections topple into the sea.
What Are Headlands?
Headlands are narrow, raised areas of land that project into the sea. They form because the rock making up the headland is harder and more resistant than the rock on either side. Waves erode the softer rock faster, creating bays, while the harder rock resists erosion and stands out as a headland.
Classic headland examples: Flamborough Head (Yorkshire, UK), Cape Byron (Australia), Land's End (Cornwall, UK).
Features on and Around Headlands
Headlands are subject to concentrated wave energy and develop distinctive erosion features:
| Feature | How it forms |
|---|---|
| Sea cave | Waves exploit joints and cracks in the headland, widening them into a cave |
| Sea arch | Two caves erode from opposite sides until they meet through the headland |
| Sea stack | The arch roof collapses, leaving an isolated column of rock |
| Sea stump | Further erosion reduces the stack to a low, exposed rocky platform |
The Twelve Apostles Marine National Park in Victoria, Australia, is famous for its sea stacks. Originally there were nine (not twelve) stacks, and their number continues to fall as individual stacks collapse. Watching a stack collapse is a once-in-a-lifetime event — and entirely natural. The stacks are made of limestone that took 10–20 million years to form and took 10,000–15,000 years of wave erosion to separate from the mainland.
Factors Affecting Cliff Erosion Rate
- Rock type: Soft rock (clay, sand) erodes quickly; hard rock (granite, limestone) erodes slowly.
- Joint density: More joints mean more places for hydraulic action to exploit.
- Fetch: Greater fetch → bigger waves → faster erosion.
- Aspect: Cliffs facing into prevailing winds erode faster.
- Human activity: Removing beach material (which absorbs wave energy) accelerates erosion.
Real world: The White Cliffs of Dover — retreating coastline
The White Cliffs of Dover in Kent, England, are one of the most recognisable coastlines in the world. Made of soft chalk, they retreat by 40–70 cm per year on average. This erosion is a real problem — coastal homes and farmland are lost to the sea every year along the nearby Holderness Coast in Yorkshire, where cliffs can erode by up to 2 metres a year. The UK government spends millions on coastal defences to slow this process.
Real world: The Twelve Apostles in Australia
The Twelve Apostles are famous sea stacks on the coast of Victoria, Australia. They formed as waves eroded limestone headlands over thousands of years — caves formed, arches developed, and when arches collapsed, stacks were left standing. When the park opened it had nine stacks (not twelve), and one collapsed dramatically in 2005. Tourists now visit to see this natural erosion process frozen in time — though eventually all the stacks will fall.
Real world: Flamborough Head and coastal defences in Yorkshire
Flamborough Head in Yorkshire (UK) is a chalk headland that juts out into the North Sea. The resistant chalk protects it compared to the softer boulder clay cliffs nearby at Holderness — one of Europe's fastest-eroding coastlines. Villages like Skipsea, which were on the clifftop 100 years ago, have already fallen into the sea, and geographers predict several more villages will be lost in the next century unless costly hard engineering solutions (sea walls, rock armour) are used.
Where do you see this in real life? If you have visited a sea cliff on holiday, the wave-cut notch at the base and the wave-cut platform you can walk on at low tide are direct evidence of the erosion processes described here.
Practice Problems
Why does a wave-cut platform form at the base of a retreating cliff?
Show answer
What is the sequence of features formed as waves erode a headland, from first to last?