geography - coasts

• what are coasts

  • a zone where the land meets and interacts with the sea
  • the coastal environment is the result of interactions between the land, water, air and living things
• zonations of a coast

  • offshore: submerged zone below low tide shoreline
  • foreshore: area between low tide and high tide shoreline
  • backshore: area from high tide shoreline to highest waterline
• why are coastal environments dynamic

  • the constant influence of natural processes and human activities means that coastal environments are everchanging and dynamic
• waves

  • waves are generated by wind blowing across the sea or oceans
  • waves can shape the coastal areas when they hit land
• tides/sea level changes

  • tides refer to the daily alternate rise and fall in the sea level
  • caused mainly by the effects of the gravitational pull of moon and earth
  • tides affect processes such as coastal erosion, sediment transport and sediment deposition
• ocean currents

  • large scale, continuous movements of water in seas and oceans
  • produced by a combination of winds, the coriolis effect and temperature differences
  • ocean currents carry cool water away from the north and south poles towards the equator and warm water away from the equator towards the poles.
• geology

  • arrangement and composition of rock found in the area
  • well jointed rocks offers more lines of weaknesses to erosion processes
  • some rock types are less resistant rocks as they are vulnerable to solution and carbonation
• types of ecosystems

  • communities of plants can interact with the environment
  • they can affect the rate of change of coastal environments (eg. burrowing)
  • coral reefs and mangroves provide as natural barriers
• human activities

  • people change coastal environments by living, trading, fishing and engaging in recreational activities in these environments.
  • eg. people alter coastlines when they build marinas and port facilities
• what are waves

  • ocean waves form when the wind blows over the surface of the ocean. the friction from the wind causes the water particles near the surface to move in an orbit, which creates the waves
• crest: highest part of the wave

  trough: lowest part of the wave
• wave height: the vertical distance between the crest and the trough

  wave length: the horizontal distance from crest to crest, or from trough to trough
• wave steepness: the ratio of wave height to wave length

  wave period: the time waves take to travel through one wavelength

  wave frequency: the number of wave crests or troughs that pass a fixed point in one second
• factors affecting wave energy

  • wind speed: how fast the wind is blowing
  • wind duration: how long the wind blows
  • length of fetch: the distance wind blows over the seas or oceans. the greater the fetch, the more energy waves have
• movements of waves: waves in the open ocean

  • long wave length, low wave height. water particles in the open ocean move in an orbit. waves approaching the shore
  • as waves moves closer to the shoreline, the water gets shallower. this causes friction between the water particles and the sea bed. the base of the waves start to slow down, resulting in the wave height increasing and wavelength decreasing. eventually, the wave becomes so steep the crest topples over. this causes the wave to break onto the coast, releasing the energy of the wave
• beach gradient

  constructive waves: gentle coastline

  destructive waves: steep coastline
• wave height

  constructive waves: low wave height

  destructive waves: high wave height
• wave length

  constructive waves: long wave length (up to 100m)

  destructive waves: short wave length (<20m)
• wave period

  constructive waves: high period (every 8-10s)

  destructive waves: low period (every 5-6s)
• wave frequency

  constructive waves: low frequency (6-9waves/min)

  destructive waves: high frequency (10-15waves/min)
• energy

  constructive waves: low energy waves

  destructive waves: high energy waves
• swash/backwash

  constructive waves: swash>backwash power

  destructive waves: backwash>swash power
• dominant process

  constructive waves: deposition

  destructive waves: erosional
• the coastal processes of erosion, transportation and deposition

  • operate at varying degrees to produce a different coastal landforms and features
  • cause changes to landforms and feature overtime
• erosion

  • hydraulic action: air in the cracks are trapped and compressed by the oncoming waves, exerting pressure on the cracks. this causes the rock to weaken and break down.
  • corrasion/abrasion: as waves break, sediments are hurled against the coast, weakening the cliffs surface and breaking down a coast. overtime, the impact is powerful enough to undercut a cliff.
  • attrition: rock particles break down and become smaller, smoother and rounder as they hit against each other
  • solution/corrosion: soluble materials in coastal rocks dissolve in the sea water, weakening and disintegrating the rocks
• transportation

  longshore current: movement of water

  longshore drift: materials are carried along the coast (movement of sediment)

  • the swash carries the sediments up onto the coast at the angle of the wind. the backwash then carries the sediments back to the sea at right angles to the coast due to the influence of gravity
  • results in zig-zag movements of sediments along the coast
• deposition

  • deposition occurs when small or low energy waves do not have the energy to carry the load.
  • sorting of the load occurs: swash brings materials onto the coast, backwash transports materials back towards the sea. backwash loses energy, deposits coarser materials first