Coasts

• Negative feedback lessens any change which has occured within the system.
• Positive feedback exaggerates the change making the system more unstable and taking it away from dynamic equilibrium.
• What are some factors affecting wave energy?

  1. Strength of the wind -> wind moves from an area of high pressure to an area of low pressure, the larger the difference in pressure gradient the stronger the winds, stronger winds = stronger waves.
  2. Duration of the wind -> wind active for longer = waves will build up and increase.
  3. Size of the fetch -> The fetch is the distance over which the wind blows + the larger it is, the more powerful the waves will be.
• Describe the sediment sources from offshore areas in a coastal system.

  • When waves, tides and currents erode offshore sediment sinks such as offshore bars,
  • helps build up the beach,
  • storm surges or tsunami waves may also transfer sediment.
• The littoral zone is the area of land between the cliff's or dunes on the coast and the offshore area that is beyond the influence of the waves.
• What are some short-term factors?

  • tides and storm surges.
• What are some long-term factors?

  • changes in sea level and human intervention.
• What are constructive waves?

  • deposit material,
  • creates depositional landforms,
  • formed by weather systems that operate in the open ocean,
  • long wavelength,
  • 6-9 per minute,
  • low waves,
  • strong swash- weak back wash,
  • occurs on gently sloped beaches.
• Describe the sediment sources from longshore drift in a coastal area.

  • sediment is moved due to prevailing winds,
  • backwash pulls the sediment directly back down the beach.
• Describe a negative feedback loop in a coastal system.

  1. When the destructive waves from the storm lose their energy excess sediment is deposited as an offshore bar,
  2. The bar dissipates the waves energy which protects the beach from further erosion,
  3. Over time the bar gets eroded instead of the beach,
  4. Once the bar has gone, normal conditions ensue and the system goes back to dynamic equilibrium.
• Describe the sediment sources from cliff erosion.

  • important in areas with unconsolidated cliffs that are eroded easily,
  • some areas: retreat up to 10m per year -> significant sediment input,
  • most erosion occurs during the winter months = more frequent storms
• Describe the sediment sources from a river.

  • most of the sediment in the coastal zone is inputted from rivers,
  • especially in high-rainfall environments,
  • sediment is deposited in estuaries, which are brackish areas.
• Dynamic equilibrium is the maintenance of a balance in natural system, despite it being in a constant state of change.
• What can upset the dynamic equilibrium?

  long term = human interventions, short term = natural variations
• Describe the sediment budget.

  • use data of inputs, outputs, stores and transfers to assess the hains and losses of sediment within a sediment cell,
  • human actions and natural variation in a system can disrupt the state of equilibrium.
• Describe wave formation.

  • winds move across the surface of the water, causing frictional drag,
  • Leads to a circular orbital motion of water particles,
  • as seabed become shallower, the orbit of the water particles becomes more elliptical,
  • wave height increases but wavelength and wave velocity decreases.
• On a coastline:

  1. Inputs- Marine: waves, tides. Atmosphere: sun, air pressure. Humans: pollution,
  2. Outputs- Ocean currents, rip tides, sediment transfer, evaporation,
  3. Stores/Sinks- Beaches, sand dunes, spits, cliffs, arches, salt marshes,
  4. Transfers/Flows- Erosion, weathering, transportation, deposition,
  5. Energy-wind, waves.
• Describe a positive feedback loop in a coastal system.

  1. People walking over sand dunes destroys vegetation growing there and causes erosion.
  2. As the roots from the vegetation have been holding the sand dunes together, damaging the vegetation makes the sand dunes more susceptible to erosion, which increases the rate of erosion.
  3. Eventually the sand dunes will be completely eroded leaving more of the beach open to erosion taking the beach further away from its original state.
• The sediment cells are an area of the coast which is bordered by prominent headlands.
• Strength of the wind can affect wave energy. Different pressure areas can cause a variation in surface heating by the sun. The larger the difference in the pressure gradient, the stronger the winds
• Duration of the wind can affect wave energy. If the wind is active for longer periods of time, then the energy of the waves will build up and increase
• Size of the fetch can affect wave energy. The larger the fetch the more powerful the waves will be
• Constructive waves:

  • formed by weather systems that operate in the open ocean,
  • long wavelength,
  • 6-9 per minute,
  • low waves,
  • strong swash,
  • weak backwash,
  • occurs on gently sloped beaches
• Destructive waves:

  • localised storm events with stronger winds operating closer to the coast,
  • short wavelength,
  • 11-16 minute,
  • high waves,
  • weak swash,
  • strong backwash,
  • occurs on steeply sloped beaches
• The type of waves in a coastal environment may vary:

  • Summer: constructive waves dominate
  • Winter: destructive waves dominate,
  • constructive waves may become destructive if a storm begins,
  • climate change may increase the storm frequency within the UK,
  • Coastal management may affect the type of waves that occur
• Tides:

  • the gravitational pull of the sun or moon changes the water levels of the seas and oceans
  • difference in height between tides is called the tidal range,
  • the highest high tide and lowest low tides occur when the sun and moon are in alignment- both of their gravitational forces combine to effectively pull the oceans towards them,
  • the lowest high tide and highest low tides occur when the sun and moon are perpendicular to each other- both of their gravitational forces act against each other.
• Currents:

  • rip currents are powerful underwater currents occurring in areas close to the shoreline on some beaches when plunging waves cause a build up of water at the top of the beach,
  • a gap in a sandbar can cause rip currents,
  • riptides are when the ocean tide pulls water through a small area such as a bay or lagoon,
  • riptides are an energy source in a coastal environment and can lead to outputs of sediment from the beach area
• High-energy coastline:

  • are associated with more powerful waves,
  • area of large fetch,
  • have rocky headlands and landforms,
  • fairly frequent destructive waves,
  • rate of erosion exceeds the rate of deposition
• low-energy coastline:

  • less powerful waves,
  • occur in sheltered areas,
  • fairly sandy areas,
  • landforms of deposition as rates of deposition exceed the rates of erosion
• Wave refraction:

  • the process by which waves turn and lose energy around a headland on uneven coastlines,
  • wave energy is focused on the headlands,
  • energy is dissipated in bays
• Erosive marine processes:

  • Corrasion- sand and pebbles hurled against cliffs at high tides,
  • Abrasion- sediment is moved along the shoreline,
  • Attrition- rocks and pebbles are hit against each other,
  • Hydraulic action- air is forced into cracks, joints and faults where water may implode under the high pressure,
  • Corrosion (solution)- mildly acidic seawater can cause alkaline rocks to be eroded,
  • Wave quarrying- when the force of the breaking wave hammers the rocks surface, leaving it open to attack from hydraulic action and abrasion
• Factors affecting erosion:

  • waves- main factor, more destructive during winter and storms,
  • beaches- absorbs wave energy,
  • Subaerial processes- weathering and mass movement processes, may lead to increased corrasion and abrasion,
  • rock type- sedimentary rocks are vulnerable to erosion, igneous and metamorphic are made up of interlocking crystals,
  • rock faults- fissures, cracks and joints are weaknesses, increase rock face surface area, large faults can lead to formation of headlands and bays,
  • rock lithology
• Igneous rocks:

  • granite and basalt,
  • very slow erosion, <0.1cm/ year,
  • interlocking crystals which allow for high resistance to erosion
• Metamorphic rocks:

  • slate, schist, marble,
  • slow erosion, 0.1-0.3cm/year,
  • crystal all orientated in the same direction, resisting erosion
• Sedimentary rocks:

  • limestone,
  • very fast, 0.5-10cm/year,
  • lots of faults which makes them weak and vulnerable to erosion
• Processes of transportation and deposition:

  • traction- large sediment rolling along the sea bead,
  • Saltation- smaller sediment bouncing along the sea bed,
  • suspension- small sediment is carried within the flow of the water,
  • Solution- dissolved material is carried within the water
• Longshore drift:

  • waves hit the beach at an angle- direction of the prevailing winds,
  • the waves push sediment in the swash,
  • the wave carries sediment back down the beach in backwash
• Deposition:

  • occurs when sediment becomes too heavy or if the wave loses energy,
  • high-energy coastlines deposit larger rocks,
  • low-energy coastlines smaller sediment is deposited,
  • Flocculation- clay particles clump together due to chemical attraction and then sink due to their high density
• Weathering:

  • breakdown of rocks over time.
• Positive feedback in weathering:

  • promoting further weathering will increase the area of exposed rock,
  • increase amount of erosion,
  • increase the supply of rocks.