Processes

• Coastal processes are divided into two parts: Marine processes (offshore, water-based) and Terrestrial processes (onshore, land-based)
• Coastal processes


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


  Marine process that erodes, transports and deposits material
• Waves


  • Height and strength depend on fetch, time the wind blows, and strength of the wind
  • As a wave enters shallow water, friction from the seabed causes the wave to lean forward and eventually crest and break onto the beach
  • Movement of water up the beach is called swash, and the return movement is the backwash
• Types of waves


  • Destructive waves (erode the beach)
  • Constructive waves (are beach builders)
• Constructive wave


  • Long wavelength and low height
  • Low frequency (6-8 per minute)
  • Creates sandy, depositional beaches
• Destructive wave


  • Short wavelength and high height
  • High frequency (10-12 per minute)
  • Strong backwash
  • Creates shingle, erosional beaches
• Weathering


  The breakdown of rock in-situ (does not involve the movement of the material)
• Types of weathering


  • Mechanical (e.g. freeze-thaw)
  • Chemical
• Mechanical weathering (freeze-thaw)


  Water gets into cracks and joints in the rock, when it freezes it expands and the cracks open wider, when it thaws the crack contracts, over time this widens the crack until pieces of rock split off
• Chemical weathering


  Rainwater is slightly acidic and reacts with minerals in the rock creating new material
• Sub-aerial weathering


  • Coastal processes not linked to the action of the sea
  • Includes freeze-thaw weathering (mechanical) and chemical weathering
• Weathering


  Weakens cliffs and makes them more vulnerable to erosion
• Freeze-thaw weathering


  1. Water gets into cracks and joints in the rock

  2. When the water freezes it expands and the cracks open a little wider

  3. When the water thaws, the crack contracts, releasing pressure on the crack

  4. Over time, repeated freezing and thawing, widens the crack until pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel
• Chemical weathering


  1. Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere

  2. This reacts with minerals in the rock creating new material

  3. Rock-type affects the rate of weathering e.g. limestone chemically weathers faster than granite

  4. The warmer the temperature, the faster the chemical reaction
• Biological weathering


  1. Trees and other plants can grow within the cracks in a rock formation

  2. As the roots grow bigger, they push open cracks in the rocks making them wider and deeper

  3. Over time the growing tree eventually prizes the rock apart

  4. Burrowing animals, such as rabbits, disturb the ground above the burrow, which puts pressure on any cracks, eventually leading to pieces falling off the rock
• Mass movement


  The downhill movement of material under the influence of gravity
• Throughflow and runoff caused by heavy rain


  Can make cliffs more unstable and increase the likelihood of mass movement
• Types of mass movement

  • Landslides
  • Slumping
  • Rockfalls
• Factors affecting type of mass movement

  • Angle of slope (the steeper the slope the faster the movement)
  • Nature of regolith
  • Amount and type of vegetation
  • Water
  • Type and structure of rock
  • Human activity
  • Climate
• Soil creep


  1. Common in humid climes with the movement of less than 1cm per year

  2. Soil expands when it freezes, gets wet or is heated up in the sun

  3. As the soil expands, it lifts at right angles to the slope

  4. When the soil shrinks, it falls straight back down

  5. Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time
• Flow


  1. Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year

  2. Usually happens after the soil has become saturated with a flow of water across the surface

  3. Vegetation is flattened and carried away with the soil
• Slide


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


  1. Slopes are steep and movement is rapid

  2. Caused by a number of reasons: Extreme weathering, Rainfall, Earthquakes, Hot weather
• Slump


  1. Usually found on weaker rock types (i.e. clay), that become saturated and heavy

  2. This is common at the coast and is also known as rotational slip

  3. It involves a large area of land moving down the slope in one piece

  4. Because of the way it slumps, it leaves behind a curved indented surface
• Erosion


  Destructive waves are responsible for the majority of erosion that happens along a coast. They carve the coastline in four main ways: Hydraulic Power/Action, Attrition, Abrasion, Corrosion.
• Longshore drift


  The process where the waves transport material, such as sand along the beach in the direction of the prevailing wind. The swash moves material up the beach at an angle as the waves approach in a similar direction to the wind. The material then moves back down the beach at 90° due to gravity, this is the backwash. This movement continues along the beach in a zig-zag motion in the direction of the prevailing wind.
• Deposition


  Occurs when transported material is dropped from the sea water when the velocity (speed) of the water flow slows down and there is not enough force to hold/suspend the material in the water anymore. Beaches are formed of sediment deposited in bays. Saltmarshes and mudflats are formed in sheltered estuaries, usually behind spits.