Coastal landscapes

• Define and explain an open system

  >Sediment and material of inputs and outputs can cross system boundaries

  • inputs: kinetic energy from wind and waves, thermal energy from the sun
  • outputs: marine and wind erosion from beaches and rock surfaces
  • throughputs: LSD, backwash and swash
• Define and explain a closed system

  > sediments and material of inputs and outputs do not cross system boundaries

  Matter is contained within the system driven by the sun's energy.

  Some may be transferred between neighbouring sub-cells by wind
• What is a sediment cell?

  Linked system of inputs, throughputs and outputs of sediment along the section of coastline which is mostly self contained.

  In the UK there is 11 cells determined by the shape of the coastline.
• How does sediment move within and between cells?

  >sediment is eroded from depositional sink landforms

  >this is then carried offshore and re-transported onshore by currents, wind action, fluvial deposition, erosion and mass movement of cliffs.
• Physical factors that affect the coastal landscape system

  Wind, waves, tides, geology and currents
• How does wind affect the coastal landscape system

  >it acts as a moving force

  >aeolian processes such as erosion and abrasion lead to transportation of small sediment affect the coast directly

  >strong prevailing winds generate LSD, leading to a higher fetch and higher wave energy and refraction exacerbating the force of wave erosion on the coastline
• > Constructive waves: have low height, long wavelength and a low frequency.

  • They break as spilling waves
  • swash energy exceeds backwash energy, so material is slowly moved up the beach

  > Deconstructive waves: have a greater height, shorter wavelength and a high frequency.

  • They break as plunging waves
  • backwash energy exceeds swash energy, so not much material is moved up the beach and is transported offshore
• > Spilling waves: waves that gently break onto gently sloping beaches and water spills forward

  > Plunging waves: relatively steep waves break onto steep beaches and water plunges vertically down when the crest curls

  > Surging waves: low angle waves break onto steep beaches where the wave slides forward and may not break
• Energy of a wave

  P=H^2 x T

  P=power

  H=height

  T=time
• How do tides affect the coastal landscape system?

  • moon pulls water towards it creating a high tide due to gravitational pull
  • this creates a compensatory bulge on the opposite side of the earth
  • between these bulges there will be a low tide
  • this range influences where wave action occurs as well as the weathering processes, processes between the tides and scouring
• How does geology affect the coastal landscape system?

  Structure:

  • properties of individual rock types: fault, bedding joints permeability (pores)

  Lithology:

  • physical and chemical make up of rocks which are impacted by weathering, mass movement and erosion

  Rocks all have different strengths and give off different amounts of sediment impacting the coasts differently, e,g:

  -chalk is porous

  -limestone is carbonate and permeable

  -sandstone is permeable

  -slate is impermeable

  -granite is impermeable - igneous rock
• > Discordant coastline: rocks lie perpendicular to the coast

  - found with headlands and bays

  > Concordant coastline: rocks lie parallel to the coast
• How do currents affect the coastal landscape system?

  > Longshore currents:

  waves approach at an angle

  current of water is parallel to the shoreline

  sediment is transported parallel to the line

  
• How do currents affect the coastal landscape system?

  Rip currents: currents move away from shoreline due to a build up of seawater and energy at the sea.

  As the backwash retreats it erodes the surface of the coastline

  
• How do currents affect the coastal landscape system?

  Upwelling currents:

  currents circulating laterally

  deep cold currents displace warm surface water
• Terrestrial sources of sediment

  > river sediment is an input to sediment budgets

  > wave erosion influences cliffs and boulders by rising sea levels

  > LSD can supply sediment from one coastal area to another

  > before it can come from erosion, sub aerial erosion, weathering and mass movement usually occurs
• Offshore sources of sediment

  > Constructive waves bring sediment back to shore from offshore locations and deposit it through marine deposition

  > Winds and strong currents can influence this

  > Shallow water leads to more friction on waves, reducing the impact of wave erosion
• Human sources of sediment

  > Beach nourishment is used when beaches are in a sediment deficit

  through lorries and pipelines offshore which hold sediment mixtures in large amounts. Water then drains away leaving sediment behind for bulldozers to spread.
• Erosion: Wave and River processes

  • Abrasion: material in water is thrown at the coastline
  • Attrition: smooth, smaller particulates form as rocks rub
  • Hydraulic action: air and water becomes trapped exerting pressure on faults in rocks
  • Solution: dissolving minerals (weak carbonic acid formed from water and dissolved co2 reacting with carbonate rocks)
  • Pounding
• Erosion: Aeolian processes

  • Abrasion: polishing and scouring of rock surfaces by wind-carried sediment grains
  • Deflation: removal of solid sediment grains by the wind
• Sub-aerial processes: land-based processes occurring above the waterline
• Mass movement: movement of material down a slope due to gravity.

  >Rock fall: rocks become detached by physical weathering

  >Sliding: slumps occur as a result of of undercutting by wave erosion
• Wave, river and aeolian processes: transportation

  • Traction: larger particles are pushed and rolled along the seabed
  • Saltation: short irregular transport of heavier material
  • Suspension: small particles of sand /silts
  • Solution (in rivers/waves): dissolving minerals (e.g. by weak carbonic acid)
• Wave, river and aeolian processes: deposition

  > flocculation of clay particles which then sink to the sea bed

  > deposition of material when wind speeds fall due to surface friction or a barrier
• Weathering - physical

  -freeze thaw

  -salt crystallisation (precipitates of salts form crystals in rock causing stress and crack formations)
• Weathering - Chemical

  • Carbonation : co2 in rainwater forms carbonic acid weathering away carbonate rocks like limestone and chalk
  • Solution
  • Oxidation
  • Chelation: decomposition of plant material

  these organic acids make soils acidic which combine with water to weather away minerals in rocks

  • Lithification: sediments sink to ocean floor, forming sedimentary rocks
• Formation of erosional landforms - Bays and Headlands


  Alternating bands of hard rock (limestone) and soft rock (clay) forming a discordant coastline.

  Formed as a result of hydraulic action, abrasion and pounding from wave erosion and potentially weathering.
• Weathering - Biological

  • Organic acids from leaf litter and decomposition causes acidic acid to interact with minerals through chelation.
  • Tree roots grow through faults and cracks in rocks and exert outward pressure causing gaps to increase.
• Formation of erosional landforms - Geos and blowholes

  Geos:

  >Waves erode lower portion of the cliff forming a sea cave

  >Clifface above erodes and collapses, extending the cave further into the cliff

  
  

  Blowholes:

  >Roof of tunnel-like cave collapses along a master joint forming a vertical shaft reaching the cliff top

  >Hydraulic pressure is released in gaps within the clifftop as aerated water
• Formation of erosional landforms - Caves, arches, stacks and stumps

  1> Hydraulic action, freeze thaw and salt crystallisation expands crack to a cave

  2> mass movement of weakened material as a result of weathering ans hydration causes arch to appear

  3> further pounding and weathering causes further collapse forming stacks and stumps
• Formation of erosional landforms - Cliffs and shore platforms

  1> undercutting of cliffs by abrasion, corrasion and pounding forms a wave cut notch

  2>further undercutting weakens support for above rock strata

  3>this collapses and a steep profile and cliff forms

  4>mass movement of debris at cliff foot ensures a steep cliff profile that retreats inland parallel to the coast

  intertidal zone is formed by erosion of cliffs that are exposed to sub-aerial weathering, friction and abrasion of high and low tides.
• Rock strata of cliffs

  Horizontal: undercutting from waves

  rocks fall and retreat parallel to the coast

  
• Rock strata of cliffs

  Seaward dipping strata: undercutting from waves removes basal support of cliff, so rocks slide into bedding planes in the sea

  
• Rock strata of cliffs

  1> Landward dipping strata: erosion from waves and weathering undercuts the cliffs

  2> rocks dip gently seaward with nearly vertical joints

  3> steep profile is formed due to mass movement as gravity pulls loose rocks down slope

  4> rocks dip inland producing a stable, steep cliff profile

  
• Deposition - lack of velocity and energy causes sediment to settle in low energy environment.

  Occurs in LSD, swash, backwash
• Formation of depositional landforms - Beaches

  Swash aligned : formed by constructive waves which build up large profiles

  Drift aligned : formed by angle waves which move sediment down coast building narrow profiles

  Sandy: gentle sloping profile where some sediment goes back down beach forming ridges and runnels

  Shingle: steeper profile with larger materials deposited at the top
• Depositional landforms in beaches

  Ridge: depression between intertidal bars

  formed by the interaction of waves, currents and sediment

  
• Depositional landforms in beaches

  Ridge: raised surface of sand from underlying beach material deposited by waves and runs parallel to the shoreline.

  
• Movement of sediment by wave action - littoral transport
• Formation of a spit

  material is deposited near a coastline with the contribution of LSD

  deposition is caused by a decrease in water velocity and energy.