Coasts

• What is a system?

  A set of interrelated components working together towards some kind of process.
• What is an open system?

  Where matter and energy can be transferred from the system across and beyond the boundary into the surrounding environment.
• What is a closed system?


  These have transfers of energy both into and beyond the system boundary but not transfer of matter
• What is an isolated system?


  No interactions with anything outside the system boundary. No input or output of energy or matter
• What is dynamic equilibrium?


  The balanced state of a system when it's inputs and outputs are equal. If one element changes because of an external influence, this affects the internal equilibrium and affects other components of the system. By a process of feedback, the system adjusts to the change and regains equilibrium.
• What is positive feedback?


  Where the effects of an action are amplified or multiplied by subsequent or secondary knock-on effects.
• What is negative feedback?

  Where the effects of an action are nullified by its subsequent knock-on effects.
• coastal zones - backshore

  Area between high water mark (HWM) and the landward limit of marine activity. Changes normally take place here only during storm activity.
• Give the inputs, components and outputs in a coastal environment.


  Inputs:

  - Energy from wind, waves, tides & sea currents

  - Sediment from rivers, cliff erosion, wind, LSD

  - Geology of the coastline

  - Sea level change

  
  

  Components:

  -Erosional and depositional coastal landforms

  
  

  Flows/transfers:

  - Erosion

  - Weathering

  - Mass movement

  -LSD

  
  

  Outputs:

  - Dissipation of wave energy

  - Accumulation of sediment above the tidal limit

  - Sediment removed beyond local sediment cells
• Explain wind as an input of energy in a coastal system.


  - Prevailing wind direction: controls the direction waves approach the coastline + direction of transport of material in the coastal zone

  - Fetch: Distance of open water which a wind blows. Length of fetch helps determines magnitude + energy of waves reaching the coast

  - Frictional drag: Waves are created by transfer of energy from wind blowing over the sea surface

  - Wind can pick up + remove sediment from the coast - use it erode landforms (abrasion)
• Explain waves as an input of energy in a coastal system.


  - Waves are driven by wind

  - Wave formation: The surface of sea exerts frictional drag on the lowest layer of the wind. Higher layers of the wind move faster over lower levels and fall forward, pushing down on the sea surface, creating a wave.

  - As waves approach shallow water, friction with the seabed increases + base of wave slows down --> wave increases in height + gradient (more steep)
• What are constructive waves?

  - Low height (less than 1m)

  - Long wavelength

  - Low frequency = fewer than 10 a minute

  - Low energy waves

  - Beach gradient = flat

  - Main process = deposition

  - Stronger swash +weaker backwash
• What are destructive waves?


  - High height (more than 1m)

  - Short wavelength

  - High frequency = more than 10 a minute

  - High energy waves

  - Beach gradient = steep

  - Main process = erosion

  - Stronger backwash + weaker swash
• What is wave refraction?


  - The distortion (refraction) of wave fronts as they approach an irregular shaped coastline, causing the waves to become increasingly parallel to the coastline.

  - Wave height + steepness increases and wavelength decreases

  - This causes energy to be concentrated at headlands (erosion) and dissipated in bays (low-energy waves spill into bay --> deposition)
• Explain currents as input of energy in a coastal system

  - Currents: permanent or seasonal movement of surface water in seas

  - Longshore currents: Occur when waves hit coastline at an angle, generating a flow of water running parallel to the shoreline

  - Rip currents: Strong currents moving away from shoreline. Develop when seawater is piled up along the coastline by incoming waves.

  - Upwelling: Deep, denser + colder water displaces warmer surface water creating nutrient rich cold water currents.
• Explain tides as a input of energy in coastal system

  - Tides: periodic rise + fall in the level of the sea. Caused by the gravitational pull of the sun and moon.

  - Spring tides: Occur twice a month when the sun and moon align on the same side of the Earth

  - Neap tides: Occur twice a month when the Sun and Moon are at right angles to the Earth.

  Tidal range: Vertical difference in height of sea level between high and low tide
• What are tidal / storm surges?

  - Pushing of water against a coastline to abnormally high levels, usually combination of extreme low pressure + high tides
• What are the features of a low energy coast?

  - Occur in sheltered areas

  - Low energy waves --> constructive waves

  - Rate of deposition exceeds rate of erosion

  - Often have depositional landforms e..gs beaches, spits
• What are the features of a high energy coast?

  - High energy waves and

  - Steady / strong prevailing winds

  - Large fetch

  - Rate of erosion is greater than rate of deposition

  - Often erosional landforms e.g. headlands, cliffs + wave-cut platforms
• What is a sediment cell ?

  - Distinct area of a coastline separated from other areas by well-defined boundaries e.g. headlands

  - Sediment is added by deposition e.g. from wave, current and tide action

  - Sediment is removed by erosion

  - They are closed systems

  - 11 sediment cells in the UK
• What is a coastal sediment budget?

  - Balance between sediment being added to + removed from the coastal system (within a sediment cell)
• What are marine processes?

  - Operate upon a coastline and are connected with the sea (more erosion)
• What are the factors affecting rate of erosion?

  1. Waves - Main factor affecting rate + type of erosion

  2. Beach - A beach in front of a cliff will absorb wave energy

  3. Subaerial processes - Weathering + mass movement weaken cliffs

  4. Rock type - Sedimentary (e.g. limestone, chalk) are eroded the fastest and igneous (e.g. granite) the slowest
• What is hydraulic action? (marine processes of erosion)

  When sheer power of waves crashing against the cliff cause it to break.
• What is Wave quarrying?

  - When a breaking wave traps air as it hits a cliff face.

  - Force of water compresses this air into gaps in rock face --> pressure within the joint.

  - As water pulls back, air under the pressure is released + overtime the cliff face is weakened. Storms may then remove large chunks of it.
• What is abrasion?


  - When waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff, causing the cliff to break.
• What is attrition?


  When the rocks in the sea which carry out abrasion hit each other, slowly wearing down into smaller and more rounded pieces.
• What is solution (corrosion)?


  - Minerals are dissolved in the water and carried along in water
• What is salt crystallisation?

  Where evaporation of water leads to crystallisation of salts. It increases volume on a surface which exerts pressure on a rock eventually fracturing it over time.
• What is longshore drift?

  Where waves approach the shore at an angle and swash and backwash then transport material along the coast in a zig-zag motion in the direction of the prevailing wind
• What is traction (marine processes of transportation)?

  - Large stones and boulders are rolled + slid along the seabed and beach by moving seawater (high energy environments)
• What is saltation?


  - Small stones bounce or leapfrog along the seabed and beach. (high energy conditions)
• What is suspension?

  - When very small particles of sand and silt are carried along by the moving water
• What is solution?

  - Dissolved materials are transported within the mass of moving water
• What is marine deposition?

  When sea deposits material when there is a reduction in energy resulting from a decrease in velocity or volume of water
• When does deposition occur?

  - When sand + shingle accumulate faster than they are removed

  - As waves slow following breaking

  - As water pauses at the top of the swash before backwash begins

  - When water percolates into the beach material as backwash takes it back down the beach
• What is aeolin deposition?

  Refer to the entrainment, transport deposition of sediment by the wind
• What are sub-aerial processes?

  Operate on the land but affect the shape of the coastline. Material is broken down in situ remaining in or near its original position
• What is sub-aerial weathering?

  The breakdown and / or decay of rock in situ
• What is mechanical/physical weathering?

  - Freeze-thaw weathering → Water enters cracks in the rock. The water then freezes +expands, putting pressure on the surrounding rock. As is thaws + process repeats, cracks widen, and pieces of rock start to break off