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Spec mapping (AQA 7037): Paper 1, §3.1.3 Coastal Systems and Landscapes — the influence of geological structure and lithology (concordant and discordant coasts; rock resistance and permeability) on coastal landscapes, integrated with the operation of the coast as a system over time (equilibrium, thresholds, magnitude–frequency, and landscape change). This is the integrative lesson: it draws the strands of the whole course together by showing how geology (the template), process (the agent), sea-level (the framework) and time combine to produce a coherent landscape system. It links synoptically to §3.1.1 (systems, equilibrium, feedback, thresholds) and §3.1.4 Glacial Systems (structural control of landscape, the role of inherited geology). The dominant Assessment Objectives are AO1 (knowledge of lithological/structural controls and systems concepts) and AO2 (synthesising multiple factors into an integrated explanation of landscape character and change). The equilibrium/threshold analysis exercises AO3-style interpretation of change-over-time data.
Why this lesson matters. The 20-mark essays that carry the highest marks almost always require you to integrate — to explain a whole coastal landscape, not a single landform, by weaving together structure, process, sea level and time. This lesson builds that integrative muscle. The student who can argue that the Dorset coast is a system — discordant structure setting the planform, refraction routing energy onto headlands, the Holocene transgression setting the datum, and time straightening the coast toward equilibrium — is writing top-band geography.
Key Definition: Lithology refers to the physical and chemical characteristics of a rock, including its mineral composition, grain size, texture, colour and, crucially for coastal geomorphology, its resistance to erosion and permeability.
Different rock types exhibit vastly different resistance to coastal erosion:
| Rock Type | Hardness (Mohs scale approx.) | Resistance to Erosion | Permeability | Coastal Character |
|---|---|---|---|---|
| Granite | 6-7 | Very high | Very low (impermeable unless jointed) | Rugged, steep cliffs; headlands; slow retreat |
| Basalt | 5-6 | High | Low | Columnar cliffs (e.g., Giant's Causeway); resistant headlands |
| Limestone | 3-4 | Moderate-high (mechanical); vulnerable to solution | Variable (porous or pervious depending on type) | Vertical cliffs; caves; solution features |
| Chalk | 2-3 | Moderate | High (very porous — up to 40% porosity) | White vertical cliffs; wave-cut platforms; stacks |
| Sandstone | Variable (3-7) | Variable (depends on cement) | Variable | Cliffs with ledges; differential erosion along beds |
| Shale/mudstone | 2-3 | Low | Very low (impermeable) | Slumping; gentle cliff profiles; rapid retreat |
| Clay | 1-2 | Very low | Very low (impermeable; becomes unstable when wet) | Rapid cliff retreat; rotational slumping; mudflows |
| Glacial till | N/A (unconsolidated) | Very low | Variable | Fast retreat (1-5+ m/year); irregular profiles |
Permeability determines how water moves through rock, which has profound effects on cliff stability:
Porous rocks (e.g., chalk, some sandstones) have interconnected pore spaces that allow water to pass through. This can reduce surface runoff and overland flow, but saturated porous rock becomes heavy and weak.
Pervious rocks (e.g., well-jointed limestone) allow water to pass through along cracks, joints and bedding planes rather than through pore spaces.
Impermeable rocks (e.g., clay, granite, shale) do not allow water to pass through. Surface runoff is high, and water accumulates at the junction between permeable and impermeable layers, creating a spring line that can lubricate potential failure surfaces and trigger mass movement.
The spring-line mechanism is a frequent exam scenario and rewards precise explanation. Where a permeable rock (e.g. chalk or sandstone) overlies an impermeable one (e.g. clay), groundwater percolates down through the upper layer until it reaches the impermeable boundary, then flows laterally and emerges as a line of springs at the cliff face. This has two destabilising effects: it saturates the clay just below the junction, drastically reducing its shear strength, and the emerging water lubricates the contact, providing a ready-made failure plane. The result is that cliffs with a permeable-over-impermeable structure (such as the chalk-over-clay and sandstone-over-clay sequences of the Isle of Wight and parts of the south coast) are especially prone to large rotational slumps — a direct consequence of the interaction of lithology, structure and hydrology, not of any single one.
Exam Tip: Distinguish carefully between porous and pervious rocks in your exam answers. Chalk is porous (water passes through tiny pore spaces between grains); limestone is pervious (water passes through joints and bedding planes). Both are permeable, but the mechanism is different and has different geomorphological consequences. This distinction demonstrates advanced understanding.
The three-dimensional arrangement of rocks — their bedding, folding, faulting and jointing — is as important as their lithology in determining coastal form.
The angle at which rock beds meet the coastline has a critical effect on cliff stability:
| Orientation | Description | Stability | Resulting Cliff Profile | Example |
|---|---|---|---|---|
| Horizontal | Beds are flat-lying | Moderate | Stepped cliff with horizontal ledges | Whitby, North Yorkshire |
| Dipping inland | Beds slope away from the sea | High — beds lean into the cliff | Steep, stable cliff | Parts of the Dorset coast |
| Dipping seaward | Beds slope towards the sea | Low — beds slide towards the sea | Prone to landslides; gentler profile | Barton-on-Sea, Hampshire |
| Vertical | Beds are near-vertical | Variable | Erosion follows weaker beds; creates gullies and differential forms | Parts of the Hartland coast, Devon |
Joints are fractures in rock along which no displacement has occurred. Faults are fractures where displacement has occurred. Both create weaknesses that are exploited by erosion:
Research by Naylor and Stephenson (2010) at Staithes, North Yorkshire, demonstrated that erosion rates on the same rock type varied by a factor of five depending on joint density and orientation.
Where tectonic forces have folded rock layers, the resulting anticlines (upfolds) and synclines (downfolds) create patterns of differential resistance:
The Purbeck monocline is, in fact, the master structure that makes the whole Dorset coast intelligible, and weaving it through an answer demonstrates real geological understanding. This single Alpine-age fold tilted the originally horizontal Jurassic and Cretaceous beds toward the vertical along an east–west axis; because the resistant Portland and Purbeck limestones were thereby stood on edge as a narrow vertical wall parallel to the coast, they form the concordant outer barrier at Lulworth and Durdle Door — and where that wall has been breached, the soft Wealden clay behind erodes into coves. The same fold, traced eastward to the Studland–Swanage area where the strike turns to meet the coast more obliquely, produces the discordant headland-bay sequence of Old Harry and Swanage Bay. One structural cause — the monocline — thus explains both the concordant western and discordant eastern sections of the same coastline, depending only on the angle at which the tilted beds meet the sea. This is structural control at the landscape scale, and it is exactly the kind of unifying insight that lifts a regional case study from a list of landforms into a coherent system.
One of the most important structural controls on coastal form is whether the geological strata run parallel or perpendicular to the coastline.
On a concordant coastline, rock strata run parallel to the shore. This produces a relatively straight, uniform coastline because the same rock type is exposed along the entire coast.
Case Study: Lulworth Cove, Dorset
Lulworth Cove is the classic textbook example of erosion on a concordant coastline:
Adjacent to Lulworth Cove, Stair Hole represents an earlier stage in the same process — the limestone has been breached in two places, and small coves are beginning to form behind. Eventually, Stair Hole and Lulworth Cove may merge.
graph LR
subgraph "Concordant Coast: Lulworth"
A["Sea"] --> B["Portland Limestone (resistant outer band)"]
B --> C["Wealden Clay (soft - rapidly eroded)"]
C --> D["Chalk (resistant - slows erosion at back of cove)"]
end
On a discordant coastline, rock strata run perpendicular to the shore. This exposes bands of alternating resistant and weak rock to wave attack, producing a classic pattern of headlands and bays.
Case Study: Swanage Bay and The Foreland, Dorset
The Dorset coast between Swanage and Studland demonstrates discordant coastal processes:
Key Definition: A concordant coastline has rock strata running parallel to the shore, producing a relatively uniform coast. A discordant coastline has strata running perpendicular to the shore, producing headlands (resistant rock) and bays (weak rock).
The interaction between lithology and process creates distinctive coastal landscapes:
Chalk is worth dwelling on because it shows how a single lithology, through its particular combination of properties, generates a whole family of characteristic landforms. Chalk is mechanically fairly weak yet uniform, so it sustains near-vertical faces; it is highly porous (up to 40%), so groundwater flow and basal springs contribute to instability; it is well jointed, so hydraulic action readily exploits lines of weakness to cut caves, arches and stacks; and it is soluble, so chemical solution pits and channels its surfaces. The iconic chalk landscapes below are therefore not a coincidence but the predictable expression of these intersecting properties acting under temperate, wave-attacked conditions:
Granite produces rugged, resistant coastlines:
Soft, unconsolidated materials produce some of the most rapidly retreating coastlines:
A vital systems point about soft-rock coasts is that they are sediment sources that link distant parts of a cell. The very weakness that makes a till or clay cliff retreat fast also makes it the dominant input in its sediment budget — which is why the eroding Holderness cliffs build Spurn Point and the Humber mudflats 30–60 km away. This coupling has a profound management consequence: protecting a soft-rock cliff to save the houses on top does not merely stop local erosion, it removes a sediment input on which depositional landforms elsewhere in the cell depend, potentially starving and degrading them. The soft-rock coast is therefore best understood not as a problem to be eliminated but as the engine of the sediment cell — a perspective that reframes "erosion" from a purely destructive process into the supply side of the whole system's budget. This is the conceptual bridge between the lithology of this lesson and the management dilemmas of Lessons 9 and 10.
The Holderness coast of East Yorkshire is the fastest-eroding coastline in Europe:
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