Coasts

• Coasts are an open systems

  • inputs originate from outside the system - sediment is carried into coastal zones by rivers
  • outputs to other natural systems - eroded rock material transported offshore to the ocean
• The coast has important links with other natural systems like the atmosphere, tectonics, ecosystems and oceanic systems

  • linked together by flows of energy and by the transfer of material
• what are inputs?


  material or energy moving into the system from the outside

  • precipitation and wind
• what are outputs?

  material or energy moving from the system to the outside

  • ocean currents, rip tides, evaporation, sediment transfer
• what are stores/components?


  the individual elements or parts of a system

  • beach, sand dunes, nearshore sediment
• what are flows/transfers?


  links or relationship between the components

  • wind blown sand, mass movement processes, longshore drift
• what is positive feedback?


  Amplifies the change in inputs and outputs - moving the system further from its previous state
• what is negative feedback?


  counteracts the change in inputs and outputs to keep the system closer to its previous state
• Dynamic equilibrium: represents a state of balance within a constantly changing system
• Store:

  • beaches, sand dunes, spits, tidal flats, bars and tombolas, headlands and bays, cliffs, wave cut platforms
• 3 main material or energy inputs:

  1. marine = waves, tides, salt spray
  2. atmospheric = sun, air pressure, wind speed and direction
  3. humans = pollution, recreation, settlement, defences
• primary source or energy is the sun
• Factors affecting wind energy:

  • strength of the wind - determined by pressure gradient
  • duration of the wind - longer the wind blows = more powerful waves
  • fetch - distance of open water over which the wind blows
• Sources of energy 2 - waves:

  • frictional drag creates ripples or waves
  • orbital motion of water
  • water becomes shallower and orbit changes to elliptical shape
  • wavelength and velocity decreases
  • wave height increases
  • rises and topples over - swash up the beach and backwash down
• constructive waves:

  • low surging waves with long wavelength
  • strong swash and weak backwash
  • beach gain
  • gentle beach profiles
• destructive waves:

  • local storms responsible
  • huge plunging waves
  • short wavelength
  • beach loss
  • weak swash strong backwash
  • steeper beach profiles - overtime they will flatten the beach
• Sources of energy 1 - Wind

  • created by air moving from areas of high pressure to areas of low pressure
  • During storms - pressure gradient is hing her and winds stronger
  • prevailing winds - constantly blown from one area
  • causes high energy waves
  • day - air above land heats up faster than over water
  • warm air over land expands and rises
  • heavier cooler air rushes in takes its place - creates wind
  • at night winds are reversed because air cool up faster over land
• Wave refraction:

  waves turn and lose energy around a headland or uneven coastlines

  • energy focused on the headlands - creates erosive feature
  • energy dissipates in bays - forms low energy feature like beaches
• Sources of energy 3 - tides:

  • changes in water level of seas and oceans caused by gravitational pull of moon and sun
  • UK coastline experience two low and two high tides a day
  • highest tide during spring tides - sun and moon in line, large tidal range
  • lowest during neap tides - moon at right angle to sun, small tidal range
• Sources of energy 4 - currents:

  • rip current are strong localised underwater currents that are formed when a series of plunging waves cause a temporary build up of water at the top of the beach
• sediment cells:

  • a largely self contained stretch of coastline
  • closed systems - doesn‘t usually get transfers
• sediment sources- rivers

  • high rainfall environments where active river erosion occurs
  • sediment transported in rivers often accounts for the vast majority of coastal sediment
  • sediment deposited in river mouths and estuaries where it is reworked by waves, tides, and currents
• sources of sediment - cliff erosion

  • this can be extremely important in areas of relatively soft or unconsolidated rock
• sources of sediment - lsd

  • sediment is transported from one stretch of coastline to another stretch of coastline
• sources of sediment - wind

  • can cause sand to be blown along or up a beach
  • sometimes forms sand dunes
• sources of sediment - glaciers

  • some glaciers flow directly into ocean depositing sediment that was stored in the ice
  • occurs when glaciers calve
• sources of sediment - offshore

  • waves, tides and currents eroding offshore sediment sinks like bars
  • builds onto beach
  • storm surges or tsunami waves may also deposit sediment onto the coastline
• geomorphological processes - erosion

  • collaborative processes involving removal of sediment from a coastline
• geomorphological processes - wave quarrying

  • breaking waves hit cliff face - exert pressure
  • similar to hydraulic action
  • acts with more pressure to directly pull away rocks from a cliff face or remove smaller weathered fragments
• geomorphological processes - corrasion

  • sand and pebbles picked u by sea from offshore sediment sink or temporal store
  • hurled against cliff face at high tide
• geomorphological processes - corrosion

  • mildly acidic seawater can cause alkaline rock such as limestone to be eroded
• geomorphological processes - abrasion

  • sediment along shoreline moved causing it to be worn down over time
• geomorphological processes- attrition

  • wave action causes rocks and pebbles to hit each other
• geomorphological processes - hydraulic action

  • wave crashes onto cliff face - air is forced into cracks forcing part and widening cracks
  • air expands and rocks break apart
• mangroves stopping soil erosion