Changing Coastal Environments » Cliff and Wave-cut Platform Development

What you'll learn this session

Study time: 30 minutes

The processes involved in cliff formation and erosion
How wave-cut platforms develop over time
The factors affecting the rate of coastal erosion
Key coastal landforms created through erosion processes
Real-world examples of cliff erosion and management

Cliff and Wave-cut Platform Development

Coasts are dynamic environments where the land meets the sea. They're constantly changing due to the relentless action of waves, weather and gravity. Among the most dramatic coastal features are cliffs and wave-cut platforms, which form through the persistent processes of coastal erosion.

Key Definitions:

Cliff: A steep rock face formed at the coast by erosion.
Wave-cut platform: A gently sloping rocky surface formed at the base of a cliff by wave erosion.
Erosion: The wearing away and removal of rock by the action of waves, weather and other processes.
Hydraulic action: The force of water being pushed into cracks in the cliff.
Abrasion: The scratching and scraping of a cliff by rock particles carried by waves.

How Cliffs Form and Erode

🌊 Wave Erosion Processes

Waves attack the base of cliffs through four main processes:

Hydraulic action: Waves force air into cracks in the cliff, creating pressure that widens them.
Abrasion: Waves throw rocks and pebbles against the cliff, wearing it away like sandpaper.
Attrition: Rocks and pebbles in the water collide and become smaller and rounder.
Solution/Corrosion: Sea water dissolves some rocks, particularly limestone.

☂ Weathering Processes

Cliffs are also weakened by weathering:

Freeze-thaw: Water enters cracks, freezes and expands, widening the cracks.
Salt crystallisation: Salt water enters cracks, evaporates and salt crystals grow, putting pressure on the rock.
Biological weathering: Plants and animals can break down rock.
Chemical weathering: Rainwater (slightly acidic) can dissolve some rocks.

The Formation of Wave-cut Platforms

Wave-cut platforms form through a sequence of processes that happen over many years:

💪 Stage 1: Undercutting

Waves attack the base of the cliff, eroding it faster than the top and creating a wave-cut notch.

💥 Stage 2: Collapse

As the notch deepens, the cliff becomes unstable. Eventually, the unsupported rock above collapses.

🔁 Stage 3: Retreat & Platform

The cliff retreats inland, leaving a gently sloping rocky platform that's exposed at low tide.

This process repeats continuously, with the cliff gradually retreating inland and the wave-cut platform extending outward. Over time, the platform itself may help protect the cliff by causing waves to break further away.

Factors Affecting Cliff Erosion Rates

The speed at which cliffs erode varies greatly around the UK coast, from a few centimetres to several metres per year. This depends on:

🪨 Rock Type and Structure

Hard rocks (granite, basalt) erode slowly
Soft rocks (clay, sand) erode quickly
Joints and bedding planes weaken cliffs
Dip of rock layers affects stability

🌊 Wave Energy and Fetch

Fetch - distance wind travels over water
Destructive waves cause more erosion
Storm frequency increases erosion rates
Tidal range concentrates wave energy

Features of Eroding Cliffs

As cliffs erode, they create distinctive landforms that are part of the coastal landscape:

🗻 Headlands and Bays

When a coastline has alternating bands of hard and soft rock, the soft rock erodes faster, forming bays, while the hard rock forms headlands that jut out into the sea.

🗼 Caves, Arches and Stacks

Waves erode weaknesses in headlands to form caves. When caves from opposite sides meet, they form arches. When arches collapse, isolated stacks remain.

🌊 Wave-cut Notches

These are undercuts at the base of cliffs where wave erosion is concentrated, often leading to eventual cliff collapse.

Case Study: Holderness Coast, Yorkshire

The Holderness Coast in East Yorkshire has one of the fastest erosion rates in Europe:

The coastline is made of soft boulder clay (till) deposited during the last ice age
Erosion rates average 1.5-2.5 metres per year
Over 30 villages that existed in the 1086 Domesday Book have now disappeared into the sea
The town of Mappleton has been protected by rock armour and groynes, but this has increased erosion rates further down the coast
The cliff material eroded here is carried south by longshore drift and eventually forms the Spurn Head spit

The Importance of Wave-cut Platforms

Wave-cut platforms aren't just interesting geological features - they play important roles in coastal systems:

🐻 Ecological Importance

Wave-cut platforms create rich habitats for marine life. At low tide, they form rocky shore ecosystems with rock pools that support diverse species including:

Limpets, barnacles and mussels
Seaweeds and algae
Crabs and small fish
Feeding grounds for birds

🏡 Coastal Protection

Wave-cut platforms can help protect the coast by:

Causing waves to break further from the cliff base
Dissipating wave energy across their surface
Reducing the erosive power of waves reaching the cliff
Acting as a natural form of coastal defence

Human Responses to Cliff Erosion

As cliffs erode, they can threaten homes, businesses and infrastructure. People respond to this threat in different ways:

🏗 Hard Engineering

Building structures to stop erosion:

Sea walls
Rock armour
Gabions
Groynes

🌱 Soft Engineering

Working with natural processes:

Beach nourishment
Dune regeneration
Managed retreat
Cliff regrading

📝 Management Approaches

Decision-making strategies:

Hold the line
Advance the line
Managed realignment
No active intervention

Case Study: Birling Gap, Sussex

Birling Gap on the Sussex coast demonstrates the challenges of managing eroding chalk cliffs:

Part of the famous Seven Sisters chalk cliffs
Erosion rates of 30-40cm per year on average
Several houses have been demolished as the cliff edge approaches
The National Trust has adopted a policy of "managed retreat"
Buildings and infrastructure are being moved inland rather than defending the coastline
This allows natural processes to continue and preserves the landscape for future generations

Summary: The Cliff Erosion Cycle

The development of cliffs and wave-cut platforms is a continuous cycle:

Waves attack the base of the cliff through hydraulic action and abrasion
A wave-cut notch forms at the base of the cliff
The cliff becomes unstable as the notch deepens
Eventually, the cliff collapses, with material falling onto the beach
Waves remove the fallen material, exposing the cliff to further erosion
The cliff retreats inland, leaving a wave-cut platform
The cycle continues, with the cliff gradually retreating and the platform extending

This process has shaped our coastlines for thousands of years and continues today, creating both challenges for coastal communities and spectacular landscapes that attract millions of visitors each year.

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