coasts

• coastal classifcation

  littoral zone

  • series of sub zones representing features of wider coastline from sea to land

  1. offshore
  2. nearshore
  3. foreshore
  4. backshore

  reaches dynamic equilibruim when theres a balance between inputs and outputs
• inputs and outputs of littoral zone

  sediment is both input and output determined by

  • input=actions of waves currents and wind
  • output= washed out into the sea by EROSION
• high energy coasts

  have

  • destructive waves
  • long fetches
  • high rates of erosion
  • caves
  • arches
  • stacks
  • stumps
  • cliffs
  • wave cut platforms
• low energy coasts

  have

  • constructive waves
  • shorter fetches
  • higher rates of DEPOSITION
  • spits and bars
  • beaches
  • sand dunes
  • salt marshes
• concordant coastlines

  alternating bands of hard and soft rock parallel to coast
• discordant coastlines

  alternating bands of hard and soft rock perpendicular to coast

  • erosional landforms more common bc erosion happens at different rates along coast
• pacific coasts

  concordant coastlines aka pacific coasts lead to formation of dalmatian coasts

  • made up of offshore islands and coastal inlets running parallel to coastline
  • eg lulworth cove on SW dorset coastline bc more resistant rock acts as a barrier to protect less resistant rock
• atlantic coasts

  discordant aka atlantic form headlands and bays

  • as faster eroding less resistant rock retreats eg the clays at swanage bay it leaves behind the more resistant rock as headlands
• bays and headlands

  discordant coastlines

  • retreating less resistant rock and exposed resistant rock cause a change in shape of coastline -> wave refraction
  • this change in the way waves approach coastline can cause an increase in the rate of erosion of headlands
  • leads to formation of headland features eg caves arches stacks and stumps
• dip

  angle created when rock layer forms with the horizontal bedding plane

  • can dip towards land or sea
  • to sea = gentler cliff profile more vulnerable to mass movement
  • to land = steeper cliff profile more vulnerbale to erosion eg hydrauloic action and abrasion
• joints and faults

  geological structure of rocks(formation if joints, angle of dip, faulting and folding) is caused by the deformation and stress placed on them from tectonic processes

  • rock with more joints and faults eg sedimentary rocks = more susceptible to erosion and weathering BC these processes exert forces on the weaknesses found in the layers of the rock
• lithology snf coastal recession

  bedrock lithology = when geographers talk bout physical properties of different rocks

  existnace of sedimentary igneous and metamorphic rocks affects rate of recession along a coastline
• igneous rocks

  eg basalt and granite formed from crystalisation of magma = more resistant to erosion and weathering bc

  • contain crystals which increase strength of rocks and reduce the number of lines weaknesses that would be exploited by physical processes

  can be intrusive = formed by magma inside the earth

  or

  extrusive = formed when magma escapes thro vents on earths surface

  • average rate of erosion of igneous rocks = 0.1-0.5cm per year
• sedimentary rocks

  eg limestone and sandstone form from build up compacting and hardening of sediements into layers over time by lithification

  • sedimentary rocks formed in shorter geological time period = more susceptible to erosion and weathering and erode at a faster rate comapred to rocks formed over a longer geological time eg limestone and chalk
  • average rate of erosion = 2-6cm per year
• metamorphic rock

  eg slate and marble formed by change in structure of sedimentary and igneous rocks caused by variations in heat and pressure

  process of change = metamorphosed

  • marble formed from changing of structure caused by re crystalisation of calcite

  resistant to erosion
• vegetation- sand dunes

  need continuous supply of sand powerful winds to transport sand and obstacles to trap the sand eg plants

  • transects traditionally go from mobile dunes nearest the sea eg embryo, fore and yellow to fixed dunes nearesr backshore eg grey dunes and dune slack
  • contain 2 types of plant

  1. xerophytes = withstands periods of dry weather
  2. halophytes = withstands high conc of salt from seawater
• vegetation succession on dunes

  fore dunes = sea rocket and sea crouch

  • have deep roots and can tolerate high conc of salt

  yellow dunes = marram grass

  • long deep roots and salt tolerant

  grey dunes + heathers

  • bc of higher rates of humus
• constructive waves

  characteristics

  • low frequency 6-9 waves per min
  • long and low
  • will eventually form gently sloping beaches
  • deposit material on coasts bc backwash is less powerful then the swash
  • move in elliptical motion with waves breaking w/ their little height
  • results in 'spilling' and breaking out further along the beach
• destructive waves

  characteristics

  • repsonsibel for erosional processes
  • high frequency 10-15 waves per min
  • steep and high w/ circular motion so waves break at a greater height
  • cuases wave to 'plunge' and travel a shorter distance along the beach
  • removes material from coasts bc swash is less powerful then backwash
• erosional processes

  corrosion = chemical reaction between the seawater (weak acid) and susceptible rock eg limestone
• erosional process

  hydraulic power = cuases breakdown of cliffs due to force pf water being compressed into the cracks of the rock

  • repeated action of water forced in and out of the cracks in the rock leads to breakdown of surrounding cliff
• erosional processes

  attrition = where pieces of bedload (material carried in the water) are hit against one another

  • causes them to break apart and become smaller and more rounded
• erosional processes

  abrasion = pieces of rock are picked up by waves and hit against the bed beach or cliffs which wears them away over time
• wave cut platforms and cliffs

  1. formation of wave cut notches

  cliffs created when erosion, weathering and mass movement processes cause udnercutting and collapse of unsupported rock

  destructive waves responsible for most erosion at base of cliffs

  when destructive waves lead to abrasion undercutting the cliff face a curved indent in cliff forms = wave cut notch
• wave cut shenannignansnsns

  2. collapse of wave cut notch

  • continued erosion of wave cut notches causes rock above it to become less and less stable till it collapses
• wave cut thingggngngng

  3. formation of new wave cut notch

  • waves wash away collapsed material and begin eroding away at the cliff again = new wave cut notch
• wave cut things :/

  4. formation of wave cut platform

  • over time multiple collapsing events lead to the cliff retreating leaving behind a wave cut platform
• erosion of stupid headlands

  corrosion and hydraulic action

  • destrutive waves erode weaknesses in headlands by HA and C
• headland ero- shit

  abrasion

  • becomes more important when weaknesses in the rock widen
• headlanddddd erosion yeahh

  formation of coastal landforms

  • over time it leads to caves arches stacks and stumps
• coastal landforms caused by headland erosion (CLCBHE)

  caves

  • erosion attacks lines of weaknesses in the headlands
  • when crack widens into small hollowed out area = cave formed
• CLCBHE

  arches

  • caves that have been eroded the whole way thro
  • eg durdle door on dorset coast
• CLCBHE

  stacks

  • when the top of an arch collapses bc of gravity it leaves a stack behind
• CLFBHE

  Stumps

  • continued erosion and weathering cause stack to breakdown = stump
  • can be submerged at high tide
  • stump will erode
• longshore drift

  transports material along coastlines when waves approach beach at an angle
• swash direction

  wind approaches coast at angle bc prevailing wind direction

  waves are controlled by wind so this angle will be the direction the swash moves up the beach
• backwash direction

  gravity only force that acts on the backwash so it falls back tp the sea at a right angle to coastline
• overall effect

  bc of the differenct between the anlge of the swash and the angle of the backwash the sediement repeatedly moves in the shape of a right angled triangle

  over time sediment is carried along a beach
• depositional landforms


  spits

  • when a coast changes directions at an estuary ( where a river meets the sea) LSD continues to move sediment across the inlet
  • river doesnt let spit completely join to the coast on the other side bc the river has the energy to move the sediment
  • spits are the long fingers of sadn sticking out from one side in a coastline that have been curved by secondary winds and often have salt marshes behind them
• depositional landforms

  bars

  • formed when spit grows across a bay
  • lagoons often form behind bars