systems and processes

• what are some sources of energy in a coastal system?

  Wind, Waves, Tides and currents
• Wind

  • created by air move form high to low pressure
  • during storms wind speeds can be strong and powerful
  • prevailing winds can also cause stronger waves
• Formation of Waves

  • Waves are created by wind blowing over the sea surface.
  • friction between the wind and surface creates circular motion
• Factors affecting the waves

  • Wind speed
  • fetch
• What is fetch? 


  Maximum distance of sea the wind has blown over.
• Constructive waves

  • low frequency
  • low and long
  • elliptical profile
  • deposits material
• Destructive waves

  • high and steep
  • more circular cross profile
  • higher frequency
  • removes material from the beach
• Tides

  • They are the rise and fall of ocean surfaces.
  • Caused by gravitational pull of the moon and the sun
  • Tides will affect the position which the waves break on the beach
  • Between high and low tide is where the landforms are being created and destroyed
• Currents

  • It is the general flow of the water direction caused by the winds or the variation in water temperatures and salinity
  • currents will move the material along the coasts
• High energy profiles

  • they receive high inputs levels and form large powerful waves
  • Caused by strong winds, long fetches and steeply shelving offshore zones.
  • Rate of erosion is higher than the rate of deposition.
• Low energy profile

  • small gentle waves
  • caused by gentle winds, short fetch and gently sloping shores
  • Can be due to the present of reef or island offshore that protects the coast from full power waves
  • deposition is greater than rate of erosion.
• Inputs of sediment

  • Rivers
  • sea level rise flooding river valleys and forming estuaries
  • Eroded cliffs
  • crushed shells
  • offshore deposits
• Sediment budget


  Difference between the inputs and outputs in the system

  Positive sediment budget is when there is more input than output, causing building of coastline

  negative sediment budget is when there is more output than input , causing coastal retreat
• Sediment cells 


  The coastline is divided into 11 sediment cells

  They are mainly self contained within 2 headlands creating a close system.

  Movement of one cell does not affect the movement of the other cell
• Ways to erode the coastline

  Abrasion

  hydraulic action

  caviation

  wave quarrying

  solution

  attrition
• Abrasion 


  Bits of rocks and sediment transporting by the wave smashing into each other and breaking bits off and smoothing the surfaces
• Hydraulic action


  Air is forced into the cracks and is compressed when the waves crash in. The pressure is then exerted by the compressed air and breaks off
• Cavitation


  The waves recedes and the compressed air expands violently and exerts the pressure on the rock and causes the piece to break off.
• Wave quarrying 


  Energy of the waves high enough to break off the rocks
• Solution 


  Soluble rocks dissolved in the water
• Attrition 


  Rock are being smashed against each other and breaks into smaller bits
• How is sediment transported?

  solution, suspension, saltation and traction
• solution (transportation) 


  Substances that can dissolve are being carried along in the water. For example limestone
• suspension 


  Very fine particles such as silt and clay particles are being whipped by the turbulence and carried along the water. Most eroded material is carried like this
• Traction 


  Very large bolder are being pushed along the sea bed by the force against the water
• Longshore drift 


  Swash carried the sediment up the beach which is parallel to the prevailing wind.

  Backwash will carry the sediment back into the ocean in a right angle

  Moves in a zigzag shape
• Types of Deposition 


  Marine deposition when water deposited sediement

  Aeolian deposition when wind deposit the sediment
• Cause of deposition 


  When sediment load exceeds the energy capacity carrying it. The sediments get dropped. Reasons for this include:

  • Friction increases as water reaches shallow areas and there is greater friction between the water and ground and slows down the water
  • Flow becomes turbulent as the wind or wave encounter an obstacle and the flow becomes more rougher and decreases the overall speed
• Sub-aerial processes

  Freeze-thaw, Salt weathering, chemical weathering, wetting and drying, Biological weathering
• Salt weathering

  Caused by saline water entering the pores and cracks at high tide. When the water evaporates it leaves behind the salt crystals and they expand and apply pressure of the rocks and causes it to fall off.
• Freeze-thaw weathering 


  Example of mechanical weathering. When temperatures fluctuates. Water enter the pores or cracks. The water then freezes and expands. When the water melts it leaves the pores and cracks bigger and more likely to fall off.
• Wetting and drying 


  clay containing rocks expands when wet and breaks of fragments off the rocks
• Chemical weathering

  Limestone containing rocks will dissolve when in contact with water and form carbon dioxide gas. Widens the cracks and joints and causes the joints to weaken.
• Biological weathering 


  When the spores are deposited and form roots. The roots into the joints and cracks, weakening the joints.
• Types of mass movements

  Slides, Slumps, Rockfall and mudflows
• Slides 


  material shifts in a straight line
• Slumps 


  material shifts with a rotation
• rockfall 


  material breaks up and falls
• Mudflows 


  material flows downslope
• Mass movement


  This is the movement of material due to gravity. On coastlines it caused when coast is undercut and causes an overhang which is most likely going to collapse. Unconsolidated rock are prone to collapsing due to little friction holding them together. Heavy rainfall can saturate unconsolidated rock and further reducing friction. Runoff can erode fine particles and transport them downslope.