Coastal landscapes

• Inputs to coastal systems

  • wind
  • Waves
  • Tides
  • Sea currents
• Outputs from coastal systems

  • Sediments washed out to sea
  • Sediments deposited further along the coast
• Flows/transfers within coastal systems

  1. Erosion

  2. Weathering

  3. Transportation

  4. Deposition
• Stores/components of coastal systems

  • Beaches
  • Dunes
  • Spits
• Dynamic equilibrium

  Inputs and outputs are balanced in coastal systems
• Change in one input or output

  Often causes negative feedbacks that restore the balance of the system
• Negative feedback

  System causes other changes to have the opposite effect
• Positive feedback

  Change in the system causes other changes to have a similar effect
• Wind


  • Created by air moving from high to low pressure
  • Stronger during storms due to high pressure gradient
• Strong winds

  Generate powerful waves
• Prevailing winds

  • Consistently blow from the same direction, causing higher-energy waves
• Waves

  • Created by wind blowing over sea surface
  • Wave height affected by wind speed and fetch
  • Waves break as they approach shore, with swash and backwash
• Constructive waves

  Low frequency, low height but long, powerful swash carries material up beach
• Destructive waves

  Higher frequency, high and steep, strong backwash removes material from beach
• Tides

  • Periodic rise and fall of ocean surface, caused by gravitational pull of moon and sun
• Tides

  Affect position where waves break on beach
• Currents

  • General flow of water in one direction, caused by wind or variation in temperature and salinity
  • Move material along the coast
• High energy coasts

  Receive high inputs of energy from powerful waves, have sandy coves and rocky landforms, erosion rate greater than deposition
• Low energy coasts

  Receive low inputs of energy from small, gentle waves, have salt marshes and tidal mudflats, deposition rate greater than erosion
• Sediment sources

  • Rivers
  • Sea level rise flooding river valleys
  • Cliff erosion
  • Crushed marine organism shells
  • Offshore deposits
• Sediment budget

  • Difference between sediment entering and leaving coastal system
  • Positive budget = coastline builds outwards
  • Negative budget = coastline retreats
• Sediment cells

  Lengths of coastline that are self-contained for sediment movement, processes in one cell do not affect another
• 6 main ways waves erode the coastline

  • Corrosion (abrasion)
  • Hydraulic action
  • Cavitation
  • Wave quarrying
  • Solution
  • Attrition
• Corrosion (abrasion)

  Bits of rock and sediment being carried by waves, are smashed and grinded against the seabed and cliffs, therefore becoming smoother
• Hydraulic action

  Air cracks in cliffs are compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces
• Cavitation

  As waves recede, the compressed air expands violently, again exerting pressure on rocks and causing them to break off
• Wave quarrying

  The energy of a wave as it breaks against a cliff is enough to detach bits of rock
• Solution

  Soluble rocks being dissolved in seawater
• Attrition

  Rocks smash against each other and break into smaller bits
• Processes of sediment transportation

  • Solution
  • Suspension
  • Saltation
  • Traction
• Solution

  Substances that can be dissolved are moved along with the water
• Suspension

  Very fine material, such as silt and clay particles are whipped up by turbulence and carried along the water. Most eroded material is transported this way
• Saltation

  Larger particles, such as pebbles or gravel are too heavy to be carried by suspension. Instead, they bounce along the seabed
• Traction

  Large boulders are rolled along the seabed by the force of water
• Longshore drift

  Process of sediment transported along the shore
• Swash

  Carries sediment up the beach parallel to prevailing wind
• Backwash

  Carries sediment back down beach at a right angle to shoreline
• Types of deposition

  • Marine deposition
  • Aeolian deposition
• Marine deposition

  Sediment carried by seawater is deposited
• Aeolian deposition

  Sediment carried by wind is deposited