Coasts

• What are the four transport processes?

  • Suspension
  • Solution
  • Traction
  • Saltation
• What is the process suspension?

  Fine particles of silt hang in the water. (cloudy water)
• What is the process solution?

  Minerals dissolve in the water.
• What is the process Saltation?

  Stones and pebbles bounce along the channel and hit each other
• What is the process Traction?

  This is when rocks and boulders are rolled along the riverbed by the force of the water.
• Sediment cells

  Sediment moves along the coast in sediment cells. These act as systems which inputs (sources), processes (transfers or flows) and outputs (sinks).

  
  

  Sediment budget is the amount of sediment available within a cell.

  If sediment budget falls, waves will continue to transport sediment (erosion may occur). One change has led to another called positive feedback.

  
  

  If sediment budget increases, negative feedback occurs, the sea can not carry so much and thus deposits.

  This whole process is called dynamic equilibrium.
• Sediment cells

  There are examples of positive feedback at the coast

  • As waves erode the cliff, material is released
  • This material abrades the cliff which results in even more cliff erosion

  There are also examples of negative feedback at the coast

  • As the shore is eroded, the material makes the wave-cut platform wider
  • This can absorb wave energy and reduce the impact at the base of the cliff
• Sediment cells

  A) Stores

  B) Inputs

  C) Outputs

  D) Transfers

  
• Littoral zone

  A) Offshore

  B) Nearshore

  C) Foreshore

  D) Backshore

  E) High tide

  F) Low tide

  
• Characteristics of high energy coastlines

  Destructive waves

  Exposed to strong winds and long fetches

  Higher rates of erosion than deposition

  Tend to be rocky coasts

  Steep cliffs - marine cliff profile

  Less steep cliffs - subaerial cliff profile

  Headlands, wave-cut platforms
• Characteristics of low energy coasts

  Constructive waves

  Sheltered locations with short fetch

  Higher rates of deposition than erosion

  Sandy beaches, salt marshes, estuarine and tidal mud flats

  Gentle relief

  Sediment from land and sea

  Beaches, spits, coastal plains
• Rocky coasts:

  • Rocky coasts form where there is more resistant geology
  • Steep cliffs tend to be found in high energy environments
  • Cliffs with a gentler slope tend to be found in low energy environments
  • Erosion is more dominant than deposition

  Two types of erosion may dominate along rocky coastlines:

  Marine erosion - the action of waves

  Sub-aerial erosion - weathering and mass movement
• Discordant coastlines

  A discordant coastline is one where the rock structures meet the coast at an angle - run perpendicular to oncoming waves

  Alternating rock types lead to the formation of headlands and bays
• Concordant coastlines

  Concordant coastlines are where the rock structures run parallel to the coast
• What is strata?

  Layers of rock
• What are bedding planes?

  horizontal cracks created by pauses in rock formation
• What are joints?

  vertical cracks caused by tectonic movement or contraction
• What are folds?

  the result of pressure during tectonic movement causing the rock strata to fold
• What are faults?

  the result of stress or pressure causing it to fracture
• What is the dip?

   the angle of the rock strata
• Rock classification - sedimentary

  • Erode and weather more rapidly than other types of rock
  • Form in layers
  • Have weak bedding planes
  • They are clastic which means they are made of clasts (sediment particles)
  • Are heavily jointed
  • Often have many bedding planes and fractures
• Rock classification - metamorphic

  • Have a crystalline structure
  • Are often folded and faulted
  • Are more resistant than sedimentary rock and less resistant than igneous rocks
  • The crystals have a parallel arrangement (foliation) which means they are weaker than igneous rocks 
• Rock classification - igneous

  • Erode and weather very slowly
  • Can be categorised into two types:
  • Intrusive igneous rock - forms within the ground, cools slowly, and has large course crystals 
  • Extrusive igneous rock - forms on the Earth's surface, and cools quickly, forming smaller crystals
  • Has interlocking crystals 
  • Fewer joints and weaknesses than in other rocks
• Role of vegetation on coasts

  Vegetation helps to stabilise coastlines because:

  • The plant roots help to bind the soil/sand together reducing the impact of erosion
  • Wind speeds are reduced by vegetation which decreases erosion and increases deposition
  • Dead plant material adds organic matter to the sand and eventually leads to the formation of soil
• What is attrition?

  sediment and stones are picked up by the waves and wear away at the cliff/headland
• What is hydraulic action?

  shear force of the waves forcing air at high pressure into cracks in the cliff over time this weakens the rock and causes the joint to widen
• What is corrosion?

  weak acids in seawater dissolve the rock particles
• What is attrition?

  as rocks are moved around by the water they knock into each other gradually becoming smaller and rounder
• Formation of a stump

  j

  A) crack

  B) hydraulic action

  C) larger

  D) arch

  E) stack

  F) stump

  G) crack

  H) cave

  I) hydraulic action

  J) abrasion

  K) headland

  L) stack

  M) arch

  
• Formation of a spit

  j

  A) prevailing winds

  B) angle

  C) zig-zag

  D) salt marsh

  E) deposited

  F) spit

  G) wind

  H) direction

  
• What is biological weathering?

  Rock breaks down due to organic activity 
• What is mechanical weathering?

  When rocks break down, with no chemical changes
• What is chemical weathering?

  Rock breaks down due to a chemical reaction - rock changes
• Sea level change: Eustatic

  Eustatic sea change occurs when ice on land melts and returns to the ocean, increasing the volume of water present in the sea. Usually this is accompanied by thermal changes which primarily melts land ice.
• Sea level change: Isostatic

  Isostatic sea change occurs from the downward movement of land, causing localised sea level rise. Land can be stressed downward from post-glacial adjustments, subsidence
• Emergent coastlines

  Raised beaches and fossil cliffs
• Submergent coastlines

  Lead to rias, fjords, and dalmatian coasts