Coasts

• Coastal Sources of Energy


  The power behind any change or transfer in the coastal system
• Waves


  The main source of energy at the coast, mainly generated by wind
• Waves


  • They can be caused by tectonic activity but this is much less regular
  • Wind occurs because of the rotation of the earth and differences in atmospheric pressure when different parcels of air are heated differently by the sun

  
• Wave characteristics


  Features of the wind that affect how much energy a wave has: fetch, duration and strength of the wind

  
• Tide and tidal range


  They have an important role in the energy of the waves at a coast

  
• High tidal range


  Waves only reach a particular part of the cliff for a small amount of time, and less energy is focused on that spot

  
• Low tidal range


  Waves will be concentrated on a small part of the cliff for longer, increasing the energy directed at that point

  
• Rip currents


  Localised channels of powerful, fast-moving water that cut through the breaking waves and have localised high energy

  
• High energy coastlines


  • Erosion exceeds deposition and the landforms reflect this such as headlands with arches and caves eroded into them and wave cut platforms

  
• Low energy environments


  • Deposition exceeds erosion and the coast is more sheltered, creating beaches and spits
• Waves


  Created due to friction between the wind and the surface of the sea

  
• Types of waves


  • Constructive
  • Destructive
• Constructive waves


  Formed by distant weather systems, calm local weather, short fetch; have long wavelength, low, spilling waves; strong swash, weak backwash; build up the beach with a gentle beach profile
• Destructive waves


  Formed by local storms, strong winds, high fetch; have short wavelength, high, plunging waves; weak swash, strong backwash; beach is lost and a steeper beach profile is likely in the short term

  
• The type of wave in an area can vary depending on time of year or coastal management

  
• Wave refraction


  Changes the amount of energy reaching the shore on a small local scale, concentrating wave energy at headlands and increasing the rate of erosion

  
• Sources of coastal sediments


  • Rivers
  • Cliff erosion
  • Wind
  • Glaciers
• Sediment cells


  An important way of understanding the coastal system, considered a closed system as most sediment movement is contained within the cell
• There are 11 sediment cells around the UK coastline

  
• Sediment cell


  Can be divided into sub cells where the inputs (sources), stores (sinks), transfers and outputs within the system can all be identified
• Sediment budget


  The balance between the inputs and outputs of sediment in the system
• Coastal systems should be in a state where the sediment budget is in a state of dynamic equilibrium
• Human activity and natural changes like climate change can disturb the state of dynamic equilibrium
• Types of weathering


  • Mechanical
  • Biological
  • Chemical
• Mechanical (physical) weathering


  When rocks break up with no chemical changes
• Biological weathering


  Rock breakdown due to organic activity
• Chemical weathering


  Rock breakdown due to a chemical reaction
• Freeze-thaw/frost shattering/ice wedging


  • Happens in places where nighttime temperatures often reach below freezing
• Wetting and drying


  • Occurs in the inter-tidal zone; the area is exposed at low tide but covered at high tide, causing rocks to expand when wet and contract when dry
• Salt crystallisation


  • Occurs because the salt crystals are bigger than the water molecules, exerting pressure on the rock and causing it to break down
• Exfoliation/onion skin weathering

  • Occurs in hot climates, when rocks warm up during the day and expand, then cool and contract at night, causing thin pieces to flake off
• Biological weathering


  • Nesting birds and small burrowing animals can cause rock breakdown
• Types of chemical weathering


  • Carbonation
  • Oxidation
  • Solution
• Mass movement


  The downhill movement of material under the influence of gravity
• Factors affecting mass movement


  • Angle of slope
  • Nature of regolith
  • Amount and type of vegetation
  • Water
  • Type and structure of rock
  • Human activity
  • Climate
• Soil creep


  Common in humid climates with movement of less than 1cm per year, caused by soil expanding when it freezes, gets wet or is heated up, then shrinking back down
• Flow


  Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year, usually happens after the soil has become saturated with a flow of water across the surface
• Slide


  A movement of material 'en masse' which remains together until hitting the bottom of a slope
• Fall


  Slopes are steep and movement is rapid, caused by extreme weathering, rainfall, earthquakes, or hot weather
• Slump


  Usually found on weaker rock types (i.e. clay), that become saturated and heavy, involving a large area of land moving down the slope in one piece