physical factors influencing coastal landscapes

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  • Created by: beaw18
  • Created on: 24-04-19 12:41

winds

  • winds generate wave action; the source of coastal erosion and sediment transportation
  • waves generated by frictional drag of winds across ocean surface 
  • the higher the windspeed, the longer the fetch - the larger the waves and the energy they have 
  • onshore winds blow sea towards land 
  • if wind blows at angle that is not directly to the land, this generates longshore drift 
  • wind also erodes, transports and deposits 
    • called aeolian processes 
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wave anatomy

  • waves do not move water foward, but impart a circular motion on particular molecules - rises and falls but does not move foward
  • wave anatomy: 
    • crest - highest part of wave 
    • trough - lowest part 
    • wave height - distance between crest and trough 
    • wave length - distance between adjacent crests or troughs 
    • wave frequency - number of waves per minute
    • wave period - time interval between crests 
  • swell waves - formed in open seas and travel huge distances. long wave-length with wave periods of up to twenty seconds 
  • storm waves - locally generated, short wavelength, large in height, short wave period 
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types of wave

  • breaking waves 
    • waves in shallow water (depth of half the wavelength) come into contact with sea flaw 
    • friction of seafloor changes the speed, direction and shape
    • slows down, wavelength decreases, deepest part becomes slower than crest, waves topples and breaks. 
    • 3 categories: 
      • spilling - steep waves breaking onto gently sloping beaches, water spills gently forward as wave breaks 
      • plunging - steep waves break onto steep beaches, water plunges vertically 
      • surging - low-angle waves break onto steep beaches, slide forward and may not actually break 
  • swash - water of the broken wave moving up the beach, draw back into sea is backwash 
  • constructive waves - low height, long wavelength, low frequency, break as spilling waves, swash exceeds backwash energy 
  • destructive waves - greater height, short wavelength, higher frequency, break as plunging waves, swash is less than backwash energy 
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tides

  • periodic rise and fall of sea surface produced by the gravitational pull of the moon
  • moon pulls water towards it, creating high tide, and there is a compensatory lowered tide where the moon is not facing 
  • hightide follows moon as it orbits the earth
  • highest tide occurs when sun, moon and earth are all aligned as the gravitational pull is at its strongest 
    • happens twice each lunar month, results in spring tides with highest tidal range 
  • neap tides - occur twice a month when moon and sun are at right angle to eachother, so gravitational pull is at its weakest
  • tidal range important to coastal landscape: 
    • enclosed seas such as the Mediterranean have low tidal ranges and so wave action is limited
    • where the coast is funelled, such as the Severn Estaury, tides are drastically higher or lower
    • weathering processes have the most impact on the land between tides  
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geology

  • lithology - physical and chemical composition of rocks 
    • clay has weak lithology as it has little resistance to erosion or weathering 
    • bond that make up clay are weak 
    • basalt is made of dense, interlocking crystals giving it strong lithology as it is highly resistant to erosion and weathering 
    • form coastal features such as headlands and cliffs 
    • chalk and limestone are soluable in weak acids, and are vulneral to chemical weathering 
  • structure - properties of individual rock types such as jointing, bedding and faulting as well as the permeability of rocks 
    • porous rocks - tiny air spaces seperate particles. means pores can store water - known as primary permeability
    • limestone permeable as water can seep in joints - known as secondary permeability
    • concordant coasts - rocks run parallel to coast
    • discordant coastline - rocks lie at right angles to the coast, resistant rocks headlands, less resistant form bays 
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currents

  • nearshore currents - currents which exist in nearshore zone/the surf
  • offshore currents - larger currents which exist out at sea 
  • rip currents - strong current that flows seaward from the shore 
    • important role in transportation of coastal sediments 
    • create cusps (arch pattern of sediment on beach) 
  • ocean current - larger scale phenomena generated by earth's rotation and convection 
    • set in motion by movement of winds across water surface 
    • warm currents transfer heat from equatorial regions to poles
    • cold currents transfer cold from poles to equatorial regions 
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terrestrial

  • rivers major source of sediment input - as much as 80% of coastal sediment comes from rivers in some areas 
  • sediment in rivers comes from inland erosion from water, wind and ice 
  • cliff erosion adds to sediment budget 
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offshore

  • constructive waves bring sediment to the shore from offshore locations and deposit it, adding to sediment budget 
  • tides and currents also do this 
  • wind blows sediment from other locations such as dunes 
    • aeloian material is light to be carried 
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human

  • beach nourishment is one way we tackle sediment equilibrium 
  • sand and water can also be pumped and dumped, then spread by bulldozers 
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