Coasts

• Natural system


  A model for transfer of material and/or energy in a cycle
• Coasts as an open system


  There is transfer of energy AND matter in and out of a system across a boundary into the surrounding environment
• Energy inputs


  • Wind
  • Waves
  • Tides
• Material inputs


  • Sediment
  • Biogenic
  • Change in sea level
  • Human input
• Processes and stores


  • Beaches
  • Dunes
  • Salt marshes
  • Cliff and wave cut platforms
• Outputs include energy and material - some retained within the system eg sediment moved onto beaches or longshore drift movement OR some may be transferred out of the system
• Dynamic equilibrium


  Beaches want to remain in dynamic equilibrium where inputs and outputs are equal
• Negative feedback


  Counteracts the change, eg when cliffs are weathered or rockfall occurs scree builds up which prevents further erosion
• Positive feedback


  Adds to the issue, eg human exacerbated issues
• Wind


  Caused due to difference in atmospheric pressure, the larger the gradient the stronger the wind
• Waves


  Form due to wind blowing over the water, causing frictional drag which creates ripples, if the wind is strong enough waves will form
• Factors contributing to wave size and strength

  • Wind fetch (The distance overseas the wind has travelled)
  • Wind duration
  • Depth of water
  • Strength of wind (Pressure gradient)
• Characteristics of constructive and destructive waves

  • Constructive: Strong swash/ Weak backwash, Long wavelength, Flat beach gradient, Small wave height, Low frequency, Low energy

  Destructive: Weak swash and strong Backwash, Short wavelength, Steep beach gradient, Large wave height, High frequency, High energy
• Landforms associated with constructive and destructive waves

  • Constructive: Berms

  Destructive: Storm beach
• Wave refraction


  Occurs due to irregular coastlines because all waves try to break parallel to the coastline but due to coastal landforms such as headlands and bays
• Headlands


  Cause convergence because waves want to break parallel, which causes a lot of wave energy in a small area which causes high erosion
• Bays


  Cause divergences, large area and less energy, low rate of erosion
• Longshore drift


  Occurs due to diagonal waves, backwash occurs at a right angle, causes transfer of sediment
• Spring tide


  Every 14 days when moon and sun align, causing larger tidal range with lower low tides and higher high tides
• Neap tide


  All other parts of the lunar cycle, decreased tidal range with high low tides and low high tides
• The moon has the most impact on tides due to its proximity to earth, it has a 28 lunar cycle and causes a tidal bulge, the moon orbits the earth every 24 hours
• Storm surge


  An abnormal high tide caused by low deepening atmospheric pressure and high winds, which push sea water up the coast causing it to pile up and flood
• A storm surge on the UK east coast killed 300 people, damaging houses, farmland and drowning animals due to flooding of Lincoln and Norfolk


  1953
• Sediment cells


  Closed systems which have input, outputs and transfers of sediment, in the UK there are 11 distinct cells around the coast
• Subaerial processes


  • Mechanical weathering: Freeze-thaw, Salt crystallisation, Wetting and drying cycles

  Chemical weathering: Carbonation, Oxidation

  Biological weathering: Organic matter growth
• Types of mass movement

  • Landslide

  Rockfall

  Mudflows

  Solifluction

  Rotational slumping

  Soil creep

  Runoff
• Erosional processes


  • Hydraulic action

  Abrasion

  Attrition

  Corrosion

  Corrasion
• Factors affecting rate of erosion

  • Geology

  Dipping

  Wave and wind energy

  Fetch

  Beach presence

  Human activity

  Wave steepness

  Tides

  Storm surges
• Modes of sediment transport

  • Traction

  Saltation

  Suspension

  Solution
• Deposition


  Occurs when wave energy is low and sediment becomes too heavy to transport, deposited on the beach through onshore drift and constructive waves
• Types of deposition


  • Gravity setting

  Flocculation
• Erosional landforms


  • Coves

  Wave-cut platforms

  Caves

  Arches

  Stacks

  Stumps
• High energy coastlines


  Continue to transport small sediment such as sand or shingles but larger is deposited causing rock beaches
• Low energy coastlines


  Sandy beaches due to waves with low velocity
• Types of deposition


  • Gravity setting
  • Flocculation
• Gravity setting


  The waters velocity decreases so sediment is deposited
• Flocculation


  Important process in salt and tidal marshes, clay particles clump together due to chemical attraction and then sink due to their density
• Erosional landforms


  • Abrasion
  • Hydraulic action
  • Corrosion
  • Corrasion
• Abrasion


  Sandpaper effect (causes smooth stones)
• Hydraulic action


  Pressure exerted due to trapped air from waves