Geology and Landscape Interaction

Throughout this topic, we have seen how geology underpins everything about the UK's physical landscape. This lesson brings together the key themes: how rock type and structure control the shape of coasts and river valleys, how past processes (especially glaciation) have shaped the landscape we see today, and how physical processes and human activity interact.

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Concordant and Discordant Coastlines

The arrangement of rock types relative to the coastline has a fundamental impact on coastal landforms.

Discordant Coastlines

A discordant coastline has bands of different rock types running perpendicular (at right angles) to the coast.

Feature	Detail
Rock arrangement	Alternating bands of hard and soft rock running perpendicular to the sea
Effect of differential erosion	Soft rock erodes faster → bays; hard rock resists → headlands
Resulting shape	Indented, irregular coastline with alternating headlands and bays
UK Example	Swanage Bay and Purbeck coast (Dorset) — Portland limestone and Purbeck limestone headlands alternate with clay bays

Concordant Coastlines

A concordant coastline has bands of rock running parallel to the coast.

Feature	Detail
Rock arrangement	Bands of hard and soft rock run parallel to the coastline
Effect	The outer band of hard rock acts as a barrier, protecting the softer rock behind
If the hard rock is breached	The sea rapidly erodes the softer rock behind, creating a wide cove or inlet (e.g., Lulworth Cove)
Resulting shape	More regular coastline, unless breached
UK Example	Lulworth Cove (Dorset) — the sea has broken through the outer Portland limestone barrier and rapidly eroded the softer Wealden clay behind, creating the distinctive circular cove shape

graph LR
    subgraph "Discordant Coast"
        A["Hard Rock"] --- B["Soft Rock"] --- C["Hard Rock"] --- D["Soft Rock"]
        B --> E["BAY"]
        A --> F["HEADLAND"]
        C --> G["HEADLAND"]
        D --> H["BAY"]
    end
    subgraph "Concordant Coast"
        I["Sea"] --> J["Hard Rock<br/>(parallel barrier)"]
        J --> K["Soft Rock Behind"]
        K --> L["Hard Rock Behind"]
        J -- "If breached" --> M["COVE forms<br/>in soft rock"]
    end

Lulworth Cove: A Detailed Case Study

Lulworth Cove on the Dorset coast is one of the best-known examples of a concordant coastline that has been breached.

Feature	Detail
Outer barrier	Portland limestone — hard, resistant; runs parallel to the coast
Behind the barrier	Wealden clays — soft, easily eroded
Behind the clay	Chalk — medium-hard; forms the back of the cove
What happened	The sea found a weakness in the limestone barrier (possibly a fault or joint) and broke through. The soft clay behind was eroded very rapidly, creating a wide, almost circular cove. Erosion slowed when the sea reached the more resistant chalk at the back.
Shape	Almost perfectly circular — the classic "textbook cove"
Significance	Part of the Jurassic Coast World Heritage Site; demonstrates concordant coastline evolution; one of the most visited geological sites in the UK

Exam Tip: Lulworth Cove is a superb example to use in exams because it demonstrates several key concepts in one location: concordant/discordant coastlines, differential erosion, the role of rock type, and how a breach in a resistant barrier can lead to rapid landscape change. Learn the specific rock names — Portland limestone, Wealden clay, chalk.

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How Rock Type Affects Erosion Rates

The hardness and structure of rock directly determine how quickly it erodes.

Rock Property	Effect on Erosion
Hardness (resistance)	Hard rocks (granite, basalt, limestone) erode slowly; soft rocks (clay, sand, glacial till) erode quickly
Porosity	Porous rocks (chalk, sandstone) absorb water, which can weaken them through chemical weathering or freeze-thaw
Permeability	Permeable rocks allow water to pass through, which can dissolve minerals (chemical weathering) or lubricate joints
Joints and faults	Rocks with many joints, faults, or bedding planes are more vulnerable — water penetrates the cracks, widening them through freeze-thaw or hydraulic action
Bedding planes	Horizontal layering in sedimentary rocks creates planes of weakness; erosion may exploit these
Dip of rock	Rocks dipping seaward are unstable (layers slide towards the sea); rocks dipping inland are more stable
Chemical composition	Calcium carbonate rocks (limestone, chalk) are dissolved by weak acids (carbonation); silica-rich rocks (granite) are more resistant

Erosion Rate Comparison

Rock Type	Typical Erosion Rate (coast)	Example Location
Granite	< 0.01 m/year	Land's End, Cornwall
Carboniferous limestone	0.01-0.1 m/year	Great Orme, North Wales
Chalk	0.1-0.5 m/year	Beachy Head, East Sussex
Glacial boulder clay	1-2 m/year	Holderness, East Yorkshire
Unconsolidated sand/clay	1-5+ m/year	Parts of the Norfolk coast

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Rock Type and River Valley Shape

The same principle applies to river valleys: the rock type determines the shape, gradient, and character of the valley.

Rock Type	Valley Characteristics	Example
Hard, resistant rock (granite, limestone)	Narrow, steep-sided valleys; gorges; waterfalls; slow lateral erosion	Cheddar Gorge (limestone, Somerset)
Soft rock (clay, alluvium)	Wide, shallow valleys; extensive floodplains; meanders; rapid lateral erosion	Thames Valley (clay, London Basin)
Alternating hard and soft	Waterfalls where hard overlies soft; variable valley width; rapids	High Force, River Tees (dolerite over limestone)
Limestone	Dry valleys (water sinks underground); caves and caverns; springs where water re-emerges	Yorkshire Dales — Malham Cove, Gaping Gill
Impermeable rock (granite, clay)	More surface drainage; higher flood risk; more streams and rivers	Dartmoor (granite) — high density of surface streams
Permeable rock (chalk, sandstone)	Less surface drainage; water infiltrates and flows underground; dry valleys; springs	South Downs (chalk) — dry valleys, bournes

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How Past Processes Shape Present Landscapes

Glaciation

The Pleistocene glaciation (ending approximately 10,000 years ago) is the single most important past process shaping the UK's current physical landscape. Its effects are visible everywhere north of a line from the Severn to the Wash.