UK Coastal Landscapes

Coastal processes

Weathering and mass movement

• Mechanical weathering: freeze–thaw (water in cracks expands 9% on freezing, widening joints), salt crystallisation (dissolved salts precipitate in pores, forcing rock apart), wetting and drying.
• Chemical weathering: carbonation (rainwater + CO₂ → carbonic acid attacks limestone/chalk), oxidation, hydrolysis.
• Biological weathering: plant roots in cracks, burrowing organisms.
• Mass movement: cliff collapse mechanisms:
  • Slumping: saturated cliff material slides along a curved shear plane (rotational slip). Common on soft cliffs like Holderness (glacial till).
  • Rockfall: blocks detach from hard vertical cliffs (chalk, granite).

Marine erosion (HSAC)

• Hydraulic action (H): compressed air forced into cracks by waves; when wave retreats, sudden pressure release shatters rock.
• Abrasion A [also called corrasion]: waves hurl sediment (sand, pebbles) against the cliff face, acting like sandpaper.
• Attrition A: sediment particles collide with each other as they're transported, becoming smaller and rounder.
• Corrosion C [also called solution]: seawater dissolves soluble rock (limestone, chalk). CO₂ in seawater makes it weakly acidic.

Wave energy and erosion rate depend on: fetch (distance waves travel — longer fetch = larger waves), wave frequency, rock hardness, cliff structure (bedding planes, jointing), and beach presence (beaches absorb wave energy, protecting cliffs).

Coastal transport

• Longshore drift (LSD): waves approach at an angle (driven by prevailing winds); swash moves sediment up the beach at that angle; backwash returns straight down the beach under gravity. Net movement is in the prevailing wind direction. On the English east coast, LSD moves south.
• Suspension, saltation, traction, solution: modes of transport for sediment of different sizes.

Coastal deposition

Deposition occurs when wave energy decreases: in sheltered bays, behind headlands, in lagoons.

Coastal landforms

Erosional landforms

• Headlands and bays: differential erosion of alternating hard and soft rock. Hard rock (granite, limestone) resists → headland; soft rock (clay, sandstone) erodes faster → bay.
• Caves → Arches → Stacks → Stumps:
  1. Hydraulic action + abrasion exploit joint in headland → cave.
  2. Caves on opposite sides meet → arch (e.g. Durdle Door, Dorset).
  3. Arch roof collapses → isolated stack (e.g. Old Harry Rocks, Dorset; The Stacks, Flamborough Head).
  4. Stack eroded at base → stump (visible only at low tide).
• Cliffs and wave-cut platforms: cliff undercut by erosion at high-tide level → notch → overhanging material collapses → cliff retreats, leaving a flat wave-cut platform.

Depositional landforms

• Beaches: accumulation of sand/shingle in bays/sheltered areas. Sandy beaches = gentle gradient + low-energy waves; shingle beaches = steep gradient + high-energy waves.
• Spits: long, narrow ridges of sediment extending from the land into the sea, attached at one end (e.g. Spurn Head/Spurn Point, Humberside; Hurst Spit, Hampshire). Forms where LSD continues past a bend in the coastline; recurved end (hooked tip) due to secondary wave action.
• Bars: spit grows across a bay, sealing a lagoon (e.g. Slapton Sands, Devon).
• Tombolos: spit connects mainland to an island.

Case study A: Holderness Coastline, East Yorkshire (fastest eroding coast in Europe)

Why is erosion so rapid?

• Geology: soft, unconsolidated glacial till (boulder clay) deposited during the last ice age (~10,000 years ago). Till is easily eroded — no resistant rock to slow wave action.
• Fetch: North Sea has a long fetch from the north-east; dominant waves approach from the NE.
• Longshore drift: strong southward drift removes beach material → beaches become thin → less protection for cliffs.
• Wave energy: high-energy North Sea waves.

Rate of erosion

• Average 1.5–2 metres per year — up to 10 m in storm years.
• Since Roman times, ~3.2 km of land lost; ~30 villages have disappeared (e.g. Ravenser Odd).
• Key sites: Mappleton (rock groynes installed 1991 to protect the village; B1242 coastal road), Hornsea, Withernsea.

Management at Holderness

• Hard engineering at Mappleton (1991): two rock groynes (Norwegian granite) + rock armour revetment. Cost £2 million. Trapped sediment north of groynes → beach build-up → cliff stabilised. BUT: groynes starved beaches to the south (Great Cowden, Atwick) of sediment → accelerated erosion there. Classic example of unintended consequences.
• Managed realignment: at some sites (e.g. Easington Gas Terminal → now less critical), letting the coast erode and adapting — cheaper than defending.
• Monitoring: LIDAR cliff surveys; erosion pin networks.

Case study B: Dorset coastline — Swanage Bay and Purbeck

Geology and landform variety

• Alternating bands of hard limestone (e.g. Portland Stone) and soft clays/sands run at right angles to the coast → classic concordant/discordant coastline features.
• Old Harry Rocks: chalk stacks at Handfast Point — classic arch-stack-stump sequence.
• Durdle Door: natural limestone arch at Man o' War Bay.
• Lulworth Cove: circular bay; harder Portland/Purbeck limestone breached → softer Wealden clays eroded into a cove behind.
• Chesil Beach: 29 km shingle barrier beach (bar) connecting Portland to the mainland — one of Britain's longest barrier beaches; formed by rising sea levels after the last ice age.

Management at Swanage Bay

• Rock groynes to intercept LSD (moving north-east); beach nourishment (dredged sand pumped onto beach); sea wall along the promenade.
• Debate over Durlston Head and the impacts on Poole Bay sediment cells.

Coastal management approaches

Edexcel B exam tip

Coastal questions often include resource figures (maps, photos, cross-sections). Describe the figure first (what you see), then explain the process, then evaluate any management shown. For 8-mark "Evaluate" questions: name a management strategy → explain how it works → evidence of success → evidence of failure/limitation → conclusion.