Geography Physical - Coasts

• Coastal zone


  Dynamic landscape influenced by many factors
• Littoral zone


  • Offshore
  • Backshore
  • Nearshore
  • Foreshore
• Littoral zone


  • Area of coastline where land is subject to wave action
• Rates of erosion are affected by wave action in high tides
• Rate of recession


  How fast the coastline is retreating, affected by geology and rock type
• Main types of rock


  • Igneous
  • Metamorphic
  • Sedimentary
• Igneous rock


  • Very slow erosion rate, crystalline, few joints
• Metamorphic rock


  • Slow erosion rate, crystalline, foliation (crystals orientated in one direction, produces weaknesses), often folded & fractured
• Sedimentary rock


  • Fast erosion rate, clastic, geologically young, many bedding planes and fractures
• Coastal vegetation supports sandy coastlines and protects against recession
• Sediment cells


  Sections of the coast that can be considered an open system with inputs and outputs of sediment
• The littoral zone reaches equilibrium when inputs and outputs of sediment are balanced
• Inputs to sediment cells


  • Action of waves
  • Wind currents
• Outputs from sediment cells


  • Erosion
• Sand dunes need a constant supply of sediment which is trapped by obstacles
• Plants that colonise different dune types


  • Embryo & fore dunes: sea couch, sea rocket (halophytic)
  • Yellow dunes: marram grass (teerophytic halophytic)
  • Grey dunes: heathers
• Negative feedback


  Lessens any changes that have occurred within the coastal system
• Positive feedback


  Enhances any changes that have occurred within the coastal system
• Rocky coastlines


  • High relief, form in areas of high energy, resistant rock, destructive waves
• Sandy coastlines


  • Low relief, form in areas of low energy, less resistant rock, constructive waves
• Estuarine coastlines


  • Low relief, form in river mouths, low energy areas, less resistant rock
• Faults


  Major weaknesses within strata, rocks are heavily fractured
• Joints


  Occur in most rocks in regular patterns
• Key elements of geological structure


  • Strata (different rock layers)
  • Deformation (how much rocks are tilted/reduced by tectonic activity)
• Criteria for classifying coasts

  • Formation processes (primary or secondary)
  • Sea level change (emergent or submergent)
  • Tidal range (microtidal, mesotidal, macrotidal)
  • Wave energy (low or high)
• Valentin's classification of coasts


  Recognises that coasts can be erosional, depositional, emerging or submerging, and that these effects can magnify or neutralise each other
• Cliff profile types


  • Seaward dip, shallow angle (vulnerable to rock slides)
  • Seaward dip, steep angle (very vulnerable to rock falls)
  • Landward dip, steep profile (very stable)
• Concordant coastlines


  Pacific coasts, rock strata parallel to continent
• Discordant coastlines


  Atlantic coasts, rock strata perpendicular to coastline
• Waves


  Energy moving through water, affected by wind strength, wind duration, and water depth
• Fetch


  Uninterrupted distance over which waves are generated by wind
• Swash


  Uprush of water up the beach as a wave breaks
• Backwash


  Flow of water down the beach
• Constructive waves


  • Deposition, small fetch
• Destructive waves


  • Erosion, large fetch
• Tides


  Periodic rise and fall of sea level caused by gravitational pull of sun and moon
• Amphidromic points


  Points in the ocean where the tidal bulge rotates
• Spring tides


  Highest monthly tides, when sun and moon are aligned
• Neap tides


  Lowest monthly tides, when sun and moon are at 90 degrees
• Tidal range


  Difference in level between high and low tides