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T4.3Coastal landforms: erosional (headlands and bays, caves–arches–stacks–stumps, cliffs and wave-cut platforms) and depositional (beaches, spits, bars, tombolos)

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Notes

Coastal Landforms

Coasts are shaped by a balance of marine processes (erosion, deposition, transportation) and sub-aerial processes (weathering, mass movement). Where a coast has alternating bands of HARD and SOFT rock perpendicular to the coast, distinctive landforms develop.

Erosional landforms

Headlands and bays

  • Form on discordant coastlines — alternating hard and soft rock perpendicular to the coast.
  • Soft rock (clay, sand) erodes faster forming bays; hard rock (chalk, limestone) erodes slower forming headlands that protrude.
  • Wave refraction concentrates energy on the headlands, eroding them; wave energy disperses in bays where deposition occurs.
  • Example: Swanage, Dorset — Swanage Bay (clay), Ballard Point and Peveril Point (chalk).

Caves, arches, stacks, stumps (sequence)

A classic 4-stage sequence on a chalk headland:

  1. Cave — wave action exploits a weakness (joint or fault) in the cliff base, hydraulic action and abrasion enlarge it.
  2. Arch — caves on either side of a headland meet and break through, leaving a natural bridge.
  3. Stack — the arch's roof collapses, leaving an isolated pillar of rock.
  4. Stump — the stack is undercut by waves and eventually collapses, leaving a low remnant only visible at low tide. Example: Old Harry Rocks, Dorset — currently at stack/stump stage on chalk.

Cliffs and wave-cut platforms

  • Waves erode the cliff at its base (between high and low tide marks), forming a wave-cut notch.
  • Continued erosion undercuts the cliff face → cliff collapses.
  • The cliff retreats inland, leaving a flat wave-cut platform exposed at low tide.

Depositional landforms

Beaches

  • Form in low-energy environments (bays, sheltered coasts).
  • Sandy beaches form where waves are constructive (low energy, gently sloping shores).
  • Shingle beaches form on higher-energy coasts (steeper profile).
  • Berms (ridges of deposited material) mark high tide.

Spits

  • Form where the coastline changes direction.
  • Longshore drift transports sediment along the coast in a zig-zag (swash up at the prevailing-wind angle, backwash down at 90° to shore).
  • When the coast turns, sediment continues in a straight line, building a long ridge of sand or shingle out from the shore.
  • Recurved end (hook) forms when a secondary wind direction curls the spit landward.
  • Example: Spurn Head, Yorkshire (Holderness coast).

Bars

  • A spit growing across a bay can completely seal off the bay, forming a bar with a lagoon behind it.
  • Example: Slapton Sands, Devon.

Tombolos

  • A bar that connects an offshore island to the mainland.
  • Example: Chesil Beach connects mainland Dorset to the Isle of Portland.

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Practice questions

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  1. Question 14 marks

    Formation of headlands and bays (4 marks)

    Explain how headlands and bays form on a discordant coastline. [4 marks]

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  2. Question 28 marks

    Examine the cave-arch-stack-stump sequence (8 marks)

    Examine the formation of a sequence of erosional landforms on a chalk headland (caves, arches, stacks and stumps). [8 marks]

    Level mark scheme:

    LevelMarksDescriptor
    L11–3Simple description of one or two landforms; no clear sequence; no examples.
    L24–6Some explanation of multiple stages; partial sequence; some named examples.
    L37–8Detailed explanation of all four stages with named processes; named example (Old Harry Rocks); evaluative conclusion.

    Indicative content (worked example: Old Harry Rocks, Dorset):

    Stage 1 — Cave:

    • Waves attack a chalk headland at its base. Where there is a line of weakness — a vertical joint, fault or bedding plane — hydraulic action (waves compressing air into cracks) and abrasion (sand-laden waves grinding against the rock) enlarge the weakness into a cave.

    Stage 2 — Arch:

    • If two caves form on opposite sides of a narrow headland, they may erode through to meet — forming a natural arch (bridge) of rock above the gap.
    • Continued abrasion at the base and weathering (frost, salt) on the upper surfaces enlarges the arch.

    Stage 3 — Stack:

    • The arch's roof loses support and eventually collapses under gravity, leaving an isolated pillar of rock standing offshore — a stack.

    Stage 4 — Stump:

    • Continued wave action at the base of the stack creates a wave-cut notch; the stack eventually collapses to leave only a low platform — a stump — often visible only at low tide.

    Example: Old Harry Rocks, Dorset — chalk headland of Studland Peninsula. "Old Harry" itself is a stack; "Old Harry's Wife" was a stack that collapsed in 1896 and is now a stump.

    Conclusion: the sequence is a beautiful illustration of how marine processes (hydraulic action, abrasion, undercutting) interact with sub-aerial weathering and gravity to systematically dismantle a headland over geological time. Soft rock would not show this sequence — it requires durable, jointed rock like chalk or limestone.

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  3. Question 312 marks

    Evaluate the relative importance of erosion vs deposition (12 marks)

    Evaluate the relative importance of erosion and deposition in shaping a stretch of coastline you have studied. [12 marks]

    Level mark scheme:

    LevelMarksDescriptor
    L11–4Simple description of one or two landforms; no genuine evaluation; weak/no examples.
    L25–8Discussion of erosional and depositional features; partial evaluation.
    L39–12Detailed evaluation of multiple landforms; named coast (e.g. Dorset, Holderness); weighted judgement on the relative role of each process; justified conclusion.

    Named example: the Dorset coast (Studland to Lulworth).

    Indicative content (erosional dominance):

    • Old Harry Rocks (Studland) — chalk headland at stack/stump stage; rate of cliff retreat ~0.3 m/year.
    • Lulworth Cove — formed by the sea breaching a hard limestone bar and eroding the softer clay behind it into a circular cove.
    • Durdle Door — a natural arch of Portland limestone cut by wave action.
    • Wave-cut platforms at Kimmeridge Bay and Charmouth.
    • Process drivers: powerful Atlantic swells; high tidal range; jointed sedimentary rock.

    Indicative content (depositional dominance):

    • Chesil Beach — an 18-mile shingle ridge connecting Portland to the mainland (a tombolo). Sediment graded by wave size from pea-sized in the west to fist-sized in the east.
    • Studland Bay — sandy beach within the bay, sheltered from prevailing waves.
    • Process drivers: longshore drift moving sediment east along the coast; shelter behind headlands enabling deposition.

    Indicative content (interaction):

    • Erosion of headlands provides the SEDIMENT that depositional features are built from.
    • Many features (e.g. Studland Bay) result from BOTH — erosion of soft rock to form the bay, then deposition within the sheltered bay.
    • Coast is a sediment-budget system: erosion in some places balanced by deposition in others.

    Conclusion: on the Dorset coast, erosion is the more dramatic process — producing the iconic landforms (Old Harry, Durdle Door, Lulworth) for which the coast is famous. But deposition is no less important — Chesil Beach is one of the world's great depositional landforms, and the sediment it is built from comes from upstream erosion. The two processes are inseparable parts of a single coastal sediment system; ranking them is less useful than understanding how they balance to produce the coastline as a whole.

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Flashcards

T4.3 — Coastal landforms: erosional and depositional features

7-card SR deck for Edexcel Geography (leaves batch 2) topic T4.3

7 cards · spaced repetition (SM-2)

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