Detailed Edexcel Geography A-level: Coastal Landscapes and Change — Comprehensive Notes

Open vs Closed Coastal Systems

  • The coast can be considered as an open system: it receives inputs from outside and transfers outputs to other systems (terrestrial, atmospheric, or oceanic). These systems include rock, water, and carbon cycles.
  • In some contexts (scientific research and coastline management planning), the coast may be treated as a closed system.
  • Sediment Cells are subsections of the coast that are typically treated as closed systems for sediment in normal conditions.
    • England and Wales have eleven sediment cells.
    • Components of a sediment cell:
    • Sources – where sediment originates (e.g., cliffs, offshore bars)
    • Through flows – movement of sediment along the shore via longshore drift
    • Sinks – locations of deposition (e.g., spits, beaches)
  • Dynamic equilibrium concepts:
    • A sediment cell operates in dynamic equilibrium when sediment inputs and outputs are in a constant state of change but balanced.
    • Physical and human actions can shift this equilibrium.
    • Sediment cells are not fully closed; actions in one cell can affect neighboring cells.

Feedback in Coastal Systems

  • Coastal systems have feedback mechanisms that can move the system away from or back toward equilibrium.
  • Negative feedback loops tend to restore balance after a disturbance.
    • Example: A storm erodes a large amount of beach, increasing sediment input. Negative feedback involves offshore bar formation that dissipates wave energy and protects the beach; over time the bar erodes and the system returns to dynamic equilibrium.
  • Positive feedback loops amplify changes, moving the system away from equilibrium.
    • Example: Humans walking on dunes damages vegetation, reducing root strength that holds dunes together. This increases erosion, which further destroys vegetation, continuing the cycle.

The Littoral Zone

  • The littoral zone is the part of the coast continuously influenced by wave action; it changes due to short-term (tides, storm surges) and long-term (sea-level change, climate change) factors.
  • Subzones within the littoral zone:
    • Backshore – area above high tide level; affected mainly by exceptionally high tides
    • Foreshore – area where most wave processes occur
    • Offshore – open sea
  • Valentine’s Classification describes coastlines as advancing or retreating:
    • Advancing coastlines occur when land emerges or deposition dominates
    • Retreating coastlines occur when land subsides or erosion dominates
  • Emergent or submergent coastlines can result from post-glacial adjustment (isostatic sea-level change) or other causes.

Coastal Processes and Land Forms — Erosion

  • Erosion is a collaborative process involving multiple mechanisms; no single process acts alone. Main erosion processes:
    • Corrasion (abrasion) – Sand and pebbles hurled at cliffs causing erosion; influenced by sediment size/shape, weight, quantity, and wave speed.
    • Abrasion – Sediment moved along shore wears down the coastline over time; analogy: stones rubbing on a watermelon.
    • Attrition – Sediment particles collide and round/erode each other; mainly affects sediment size, not the cliff directly.
    • Hydraulic Action – Wave pressure forces air into cracks; cracks widen as water is compressed and expands; cavitation can erode rock.
    • Corrosion (Solution) – Mildly acidic seawater dissolves certain rocks (e.g., limestone); links to carbon cycle, climate change, and coastal erosion.
    • Wave Quarrying – Breaking waves exert high pressures on cliff faces (up to ~30 tonnes per m²) to pull away rocks; stronger than hydraulic action alone.
  • Erosion is highest when:
    • Waves are high with a long fetch
    • Waves approach perpendicularly to the cliff
    • It is high tide
    • Heavy rainfall percolates through permeable rock
    • In winter, destructive waves are largest and most destructive

Vulnerability to Erosion and Rock Types

  • Rock vulnerability to erosion depends on:
    • Rock type (clastic vs crystalline): sedimentary rocks (e.g., sandstone) are more erodible; igneous/metamorphic rocks are generally more resistant due to interlocking crystals
    • Fractures and fissures – more cracks increase susceptibility, especially to hydraulic action
    • Lithology – rock type and formation conditions determine erosion rates
  • Lithology and erosion rates (typical rates):
    • Igneous – Granite, Basalt: Very slow erosion, < 0.1 cm/year; structure: interlocking crystals, high resistance
    • Metamorphic – Slate, Schist, Marble: Slow erosion, 0.1-0.3 cm/year; crystals oriented in similar directions
    • Sedimentary – Limestone: Very fast erosion, 0.5-10 cm/year; many fractures and bedding planes

Erosional Landforms

  • Sequence on pinnacle headlands forms through marine erosion:
    • Caves widen at the base and can breach through to form an Arch
    • Arch continues to widen and collapses to form a Stack
    • Marine erosion at the base of the stack leads to stump formation after further collapse
  • Wave-cut notch and platform – Marine erosion carves a notch at the cliff base; deeper notch plus weathering causes cliff collapse, leaving a platform at the base
  • Retreating cliffs – Repeated notch and platform formation results in new cliff faces and landward retreat
  • Blowhole – Interaction of a pothole (formed by chemical weathering on top of a cliff) and an enclosing cave; deeper cave and pothole may meet to form a channel for wave action

Transport and Deposition

  • Longshore Drift (LSD) – Sediment transport along the coast via longshore drift is a key mechanism; process:
    • Waves strike the beach at an angle determined by prevailing winds
    • Sediment moves up the beach in the swash
    • Sediment returns down the beach in the backwash due to gravity
    • Net sediment transport along the coast occurs over time
  • Other modes of transport:
    • Traction – Large sediment rolls along the seabed
    • Saltation – Smaller sediment hops along the seabed
    • Suspension – Fine sediment carried in the water column
    • Solution – Dissolved material carried in water
  • Effectiveness of transport depends on wave angle:
    • Swash-aligned waves – Crest approaches parallel to coast; limited longshore drift; limited up-beach transport
    • Drift-aligned waves – Large longshore drift; sediment travels far up the beach
  • Deposition occurs when waves lose energy; typically gradual and continuous
  • Gravity settling – Heavier particles settle when energy is very low
  • Flocculation – Clay particles clump due to chemical attraction and sink more quickly

Depositional Landforms

  • Spits – Long narrow landforms formed by deposition of sediment moved by LSD; may develop recurved ends and salt marsh behind sheltered bays; expressed by estuary conditions and river currents
  • Bars – Spit that crosses a bay, linking two coastlines and creating a lagoon behind
  • Tombolo – A bar or beach connecting the mainland to an offshore island; can be exposed at high tide
  • Cuspate forelands – Triangular headlands formed by longshore drift from both sides
  • Offshore bars – Sediment deposited offshore when waves lack energy to transport to shore; forms as waves break or scour seabed and deposit
  • Sand dunes – Formed from wind-blown sand deposited behind the beach under strong onshore winds; requires abundant sand and high tides; vegetation succession is key:
    • Embryo dunes – Initial sand accumulation around obstacles
    • Yellow dunes – Vegetation develops and stabilizes surface
    • Grey dunes – Soil formation with moisture and nutrients; supports more plant life
    • Dune slack – Water table rises near surface; moister habitats develop
    • Heath and woodland – Sand becomes nutrient-rich, supporting woody plants; windbreaks for inland

Stability and Sub-Aerial Processes

  • Depositional landforms are made of unconsolidated sediment and are vulnerable to change; storms erode or transport sediment, shifting the equilibrium

  • Weathering and Mass Movement (Sub-Aerial Processes)

    • Weathering is the breakdown of rocks through mechanical, biological, or chemical means
    • Mechanical (Physical) Weathering:
    • Freeze-thaw (Frost-Shattering) – Water enters cracks, freezes and expands by ~10%, widening cracks over time
    • Salt Crystallisation – Salt crystals grow in cracks from evaporating seawater, widening cracks and possibly corroding ferrous rocks
    • Wetting and Drying – Clay expands when wet and contracts when drying
    • Chemical Weathering – Chemical reactions dissolve or weaken rocks:
    • Carbonation – CO2 in rainwater forms carbonic acid that dissolves calcium carbonate rocks (e.g., limestone); links to acid rain and seawater acidity
    • Oxidation – Minerals oxidize when exposed to air, increasing volume and causing crumbling (e.g., iron oxides turning rock rusty)
    • Solution – Some minerals (e.g., rock salt) dissolve in water
    • Biological Weathering – Organisms contribute to rock breakdown:
    • Plant Roots – Roots grow into cracks, exert pressure and split rocks
    • Birds (e.g., Puffins) – Burrows weaken cliff faces
    • Rock Boring – Certain organisms secrete acids or bore into rock
    • Seaweed Acids – Seaweeds release acids that dissolve rock minerals (e.g., kelp)
    • Decaying Vegetation – Acidic runoff from decomposing vegetation increases rock dissolution
    • Mass Movement – Movement of material downslope, governed by slope, lithology, vegetation, and saturation
    • Flows – Material moves and mixes downslope (e.g., mudflows, soil creep, solifluction in periglacial regions)
    • Slides – Material retains internal cohesion and moves as a unit
      • Rock falls – On steep cliffs (>40°) due to weathering
      • Rock slides – Water reduces friction between bedding planes
      • Slumps – Saturated soil moves with rotation, creating terraced cliff profiles

  • Sub-aerial vulnerability varies with climate: colder climates favor mechanical weathering; warmer climates favor chemical weathering

Cliff Profiles and Coastline Types

  • Cliff profiles depend on rock resistance and the dip of rock strata relative to the sea
  • Many coastlines are composite (multiple rock layers), complicating profile explanations
  • Concordant coastlines – Rock strata run parallel to the coast; often feature alternating resistant and less resistant bands; can lead to:
    • Dalmatian coastlines – Rising sea levels flood wide valleys between headlands, creating island-like ridges
    • Haff coasts – Large bays crossed by spits forming extensive lagoons
  • Discordant coastlines – Rock strata run perpendicular to the coast; bays form where less resistant rocks erode faster; headlands resist erosion and focus wave energy (refraction), leading to:
    • Erosion in headlands
    • Deposition in bays (beaches)

Coastal Vegetation and Plant Succession

  • Vegetation stabilizes coastal sediment and reduces erosion by:
    • Roots binding soil
    • Providing protective cover when submerged
    • Reducing wind speed at the surface and reducing wind erosion
  • Plant types:
    • Xerophytes – Tolerant of dry conditions
    • Halophytes (brackish) – Tolerant of salty conditions
  • Plant succession on coastlines with sediment supply:
    • Pioneer plants colonize bare mud/sand; salinity limits early species
    • Deposition adds nutrients from dead vegetation, reducing salinity and enabling more species
  • Marram grass as a pioneer plant: tough, flexible, reduces water loss, deep roots up to ~3 m, tolerates temperatures up to ~60°C
  • Salt marsh succession stages:
    • Algal stage (gut weed, blue-green algae) stabilize mud
    • Pioneer stage (Cord grass, Glasswort) stabilizes mud and allows estuarine growth
    • Establishment stage (Salt marsh grass, Sea asters) creates a vegetation carpet
    • Stabilisation (Sea thrift, Scurvy grass, Sea lavender) reduces submersion
    • Climax vegetation (Rush, Sedge, Red fescue) thrives despite occasional submersion

Waves and Sea Levels

  • Coastal energy levels define coast types:
    • High-energy coastlines: powerful waves, long fetch, rocky headlands, frequent erosional dominance
    • Low-energy coastlines: sheltered areas with constructive waves, sandy beaches, depositional dominance
  • Wave characteristics:
    • Constructive waves: strong swash, weak backwash; low wave height, long wavelength; low frequency; depositional
    • Destructive waves: strong backwash, weak swash; high wave height, short wavelength; high frequency; erosional
  • Seasonal variations and climate change:
    • Summer: constructive waves dominate
    • Winter: destructive waves dominate
    • Storms may shift waves from constructive to destructive
    • Climate change could lead to stormier UK coastlines, increasing destructive wave occurrence
    • Dams can trap sediment, reducing littoral transport and potentially increasing coastal erosion downstream
    • Human activities can interfere with natural sediment supply
  • Sea level change terms:
    • Short-term sea level change: tides, atmospheric pressure variations, wind strength/direction
    • Isostatic sea level change: localised adjustments due to isostasy (post-glacial rebound/subsidence)
    • Post-glacial adjustment examples for the UK: Southern England subsides ~1 mm/year; Scotland rebounds ~1.55 mm/year
    • Tectonic activity can cause subsidence, contributing to local sea level rise
    • Eustatic rise: global sea level rise due to thermal expansion of seawater as it warms
    • Global warming increases ocean temperature and volume, contributing to sea level rise
    • Predicting sea-level change is complex due to multiple interacting factors

Risks to Coastal Environments and Human Impacts

  • Coastalisation – Movement of people toward the coast due to desirable attributes (tourism, farmland, housing) increases vulnerability to flooding
  • Storm surges – Short-term sea-level rises during depressions/cyclones; can be intensified by:
    • Land subsidence
    • Loss of natural vegetation (e.g., mangroves) which protect against extreme weather events
    • Global warming causing warmer oceans, potentially increasing frequency and intensity of storms and surges
  • Consequences for communities:
    • Lower housing and land values in high-risk areas
    • Insurance gaps or high premiums for coastal homes
    • Environmental destruction of coastal landforms, vegetation, and habitats; erosion and sediment redistribution
  • Environmental refugees – Over 1 billion people live on coasts at risk globally; about half the world’s population lives within 200 km of the coast; rising surges and erosion forecast to increase internal and international displacement

Coastal Management Approaches

  • Management approaches can be broadly categorized as hard engineering and soft engineering; both respond to erosion and flooding threats
  • Hard engineering: traditional and effective at reducing erosion in targeted areas but costly and often shifts erosion elsewhere
  • Soft engineering: aims to work with natural processes; often more sustainable but requires ongoing maintenance
  • Management options (for each sediment cell):
    • Hold the line – Defences are built to keep the shore in its current position
    • Managed realignment – Let the coastline move inland but manage the process
    • Advance the line – Defences are built to move the shoreline seaward
    • Do nothing – No defences; allow natural erosion and sediment redistribution
  • Decision factors when choosing a policy:
    • Economic value of assets to be protected (e.g., gas terminals vs. farmland)
    • Technical feasibility of engineering solutions for a given location
    • Ecological and cultural value of land, including protecting historic sites or SSSIs
  • Cost-Benefit Analysis (CBA):
    • Assess costs (construction, maintenance, demolition) against benefits (land and asset protection, economic activity)
    • Includes tangible and intangible costs/benefits
    • Policy approved when expected benefits outweigh costs (Defra 1:1 analysis)
  • Integrated Coastal Zone Management (ICZM):
    • Manage a coastal zone as a whole (sediment cell) across political boundaries
    • Recognises coasts’ importance to livelihoods and aims for sustainable development
    • Involves all stakeholders, plans long-term, and works with natural processes
  • Shoreline Management Plans (SMPs):
    • Each sediment cell has an SMP to identify natural and human activities along the coast
    • Sediment cells are treated as management units; inter-cell exchange occurs but is limited
    • Four options considered for each stretch: Hold the line, Realign, Advance the line, Do nothing

Hard Engineering – Defences (Overview and Examples)

  • Offshore Breakwater – Rock barrier placed offshore to force waves to break before reaching shore
    • Pros: Reduces wave energy at shore
    • Cons: Visually unappealing; can create navigation hazards; may affect Longshore Drift (LSD)
  • Groynes – Timber or rock structures extending into the sea to trap sediment and build beaches
    • Pros: Builds up beach; protects cliffs; can boost tourism
    • Cons: Visually unappealing; can deprive areas downwind of sediment causing increased erosion elsewhere
  • Sea Walls – Concrete barriers that absorb/reflect wave energy; often with promenades for tourism
    • Pros: Effective erosion prevention; provides recreational space
    • Cons: Visually intrusive; expensive; energy reflected to other areas may increase erosion downdrift
  • Wave energy reflected elsewhere, affecting erosion rates along the coast

Hard Engineering – Further Defences (Specifics)

  • Rip Rap (Rock Armour) – Large rocks placed to dissipate wave energy while allowing some water to pass through
    • Pros: Cost effective
    • Cons: Rocks sourced elsewhere; may not match local geology; hazard if climbed upon
  • Revetments – Sloped structures (wood or concrete) that absorb wave energy and provide a drainage path
    • Pros: Cost effective
    • Cons: Visually unappealing; requires maintenance; may not be as durable as other options

Soft Engineering

  • Beach nourishment – Sediment is dredged from offshore sources and added to the beach to restore volume
    • Pros: Builds natural beach; aesthetically pleasing; supports tourism
    • Cons: Requires ongoing maintenance; dredging can impact local ecosystems
  • Cliff regrading and drainage – Re-sloping cliffs to stabilize them and reduce failure risk
    • Pros: Stabilises cliffs; more predictable erosion
    • Cons: May look unnatural; potential for sudden cliff collapse if not maintained
  • Dune stabilization – Planting and stabilising dunes to protect inland areas
    • Pros: Natural defense; wildlife habitat; cost-effective long term
    • Cons: Establishment takes time; maintenance may be required
  • Marsh creation – Planting and/or hydrological modification to create salt marshes
    • Pros: Habitat creation; natural flood protection
    • Cons: Time consuming; may require compensation for landowners
  • Managed retreat (resilience-based retreat) – Allowing land to be eroded or flooded with planed relocation
    • Pros: Relatively low cost; maintains ecosystem services elsewhere
    • Cons: Farmers lose land; compensation may be necessary

Sustainable Coastal Management

  • Principles include:
    • Managing natural resources (fish, water, farmland) for long-term productivity
    • Creating alternative livelihoods to reduce dependency on vulnerable coastal activities
    • Educating communities and monitoring changes to adapt/mitigate
    • Managing flood risk or relocating populations if needed

Policy Conflicts and Stakeholder Impacts

  • Coastal management involves winners and losers:
    • Winners: economic beneficiaries (protected homes/businesses), environmental benefits (habitats), social benefits (community stability)
    • Losers: land/property loss, relocation, job losses, or reduced access to coastal resources
  • Attachment to place means losses can be emotionally and socially significant; inequities may arise in protection choices
  • DEFRA funding has been reduced since 2010, leading to prioritisation of funding to the most important locations
  • Arguments for no active intervention include:
    • SMPs and the wider coastal management plan consider cross-area impacts
    • Budget constraints require prioritisation

Impact of Coastal Management on Sediment Cells

  • Coastal management affects sediment transport and distribution across cells:
    • A sea wall that reflects wave energy can increase downdrift erosion and reduce sediment supply to other areas
    • Reduced erosion at the protected site means less sediment supply to adjacent beaches, potentially increasing cliff exposure to high-energy waves
    • Groynes can produce downdrift impacts by trapping sediment in one area and starving others down the coast

Key Numerical/Formula References (for quick recall)

  • Sediment cell count in England and Wales: 11 cells
  • Pothole/channel formation example in blowhole: wave energy interaction documented qualitatively
  • Mass movement thresholds:
    • Cliff angles > 40° commonly associated with rock falls and slides (mechanical weathering prominence)
  • Post-glacial isostatic adjustments (UK example):
    • Southern England subsides ≈ 1extmmyr−11 ext{ mm yr}^{-1}
    • Scotland rebounds ≈ 1.55extmmyr−11.55 ext{ mm yr}^{-1}
  • Eustatic sea-level rise linked to thermal expansion of seawater due to warming oceans
  • Wave pressures in wave quarrying up to ≈ 30exttonnesm−230 ext{ tonnes m}^{-2}
  • Erosion rates by rock type (typical):
    • Igneous: Very slow, < 0.1extcmyr−10.1 ext{ cm yr}^{-1}
    • Metamorphic: Slow, 0.1−0.3extcmyr−10.1-0.3 ext{ cm yr}^{-1}
    • Sedimentary (Limestone): Very fast, 0.5−10extcmyr−10.5-10 ext{ cm yr}^{-1}

Notes on cross-cutting themes:

  • The carbon cycle, climate change, and coastal erosion are interconnected through processes like corrosion, carbonation weathering, and sea-level rise.
  • Human actions impact coastal systems not only through direct erosion control but also via sediment supply changes (e.g., dam construction reducing river-borne sediment).
  • Management decisions require balancing economic, ecological, and social outcomes, often involving trade-offs between immediate protection and long-term sustainability.