Coastal Processes

• Coastal processes

  Divided into marine (offshore, water-based) and terrestrial (onshore, land-based) processes
• Coastal processes

  • Wave action
  • Erosion
  • Transportation
  • Weathering
  • Mass movement
• Waves

  Formed by winds blowing over the surface of the sea
• Factors affecting wave height and strength

  • Fetch
  • Amount of time the wind blows
  • Strength of the wind
• Swash

  Movement of water up the beach
• Backwash

  Return movement of water down the beach
• Types of waves

  • Destructive
  • Constructive
• Destructive waves erode the coastline in four ways: hydraulic action, attrition, corrosion, abrasion
• Abrasion

  Erosion by rubbing, like sandpaper
• Attrition

  Erosion by particles colliding and wearing each other down
• Transportation of material

  1. Traction

  2. Saltation

  3. Suspension

  4. Solution
• Longshore drift

  The movement of sediments along a coast by waves that approach at an angle to the shore but then the swash recedes directly away from it.
• Longshore driftcharacteristics


  1. Prevailing wind pushes waves at an angle to the beach

  2. Swash carries material up the beach at the same angle

  3. Backwash carries material down the beach at right angles

  4. Repeated zig-zag movement transports material along the beach
• Weathering

  Is the physical or chemical breakdown of rock in-situ (in the place where they are)
• Types of weathering

  • Freeze-thaw (mechanical)
  • Salt weathering (mechanical)
  • Chemical weathering
  • Biological weathering
• Weathering weakens cliffs and makes them more vulnerable to erosion
• Freeze-thaw weathering

  Water gets into cracks, freezes and expands, opening cracks wider
• Chemical weathering


  Rainwater reacts with minerals in rock, creating new material
• Biological weathering

  Plants and organisms grow in cracks, forcing rock apart
• Mass movement

  Downhill movement of material under the influence of gravity
• Types of mass movement

  • Soil creep
  • Flow
  • Slide
  • Fall
  • Slump
• Soil creep

  Slow downhill movement of soil, below 1cm per year
• Flow

  Occurs on slopes 5-15 degrees, after soil becomes saturated
• Slide

  Movement of material 'en masse' that remains together until hitting the bottom
• Fall

  Rapid movement on steep slopes, caused by weathering, rainfall, earthquakes, hot weather
• Slump

  Rotational slip of a large area of land on weaker rock types like clay
• Sub-aerial processes affecting cliff shape

  1. Freeze-thaw weathering weakens cliff, allowing easier erosion

  2. Chemical weathering dissolves less resistant rock faster, changing cliff shape