Coasts

• Inputs


  Wind, waves, tides and currents.
• Outputs


  Sediment washed into the sea, deposited further along the coast
• Flows and transfers


  Processes such as erosion, weathering, transportation and deposition can move sediment within the system.
• Stores


  landforms such as beaches, dunes and spits
• Example of negative feedback


  - When a change in the system causes other changes that have the OPPOSITE effect. eg.

  1) Beach is eroded

  2) The cliffs behind are exposed to wave attacks

  3) Sediment eroded from the cliffs is deposited onto the beach, causing it to grow in size again.
• Example of positive feedback


  - When a change in the system causes other changes that have a SIMILAR effect.

  1) As a beach starts to form is slows down waves.

  2) Causes more sediment to be deposited, increasing the size of the beach.

  3) The new equilibrium is reached when long-term growth of the beach stops.
• Wind


  1) Winds are created by air moving from areas of high pressure to areas of low pressure. During events eg. storms, the pressure gradient is high and winds can be very strong.

  2) Strong winds can generate powerful waves. In some areas, wind consistently blows from the same direction (this is called a prevailing wind) - this causes higher- energy waves than winds that change direction frequently.
• Waves


  1) Waves are created by the wind blowing over the surface of the sea. The friction between the wind and the surface of the sea gives the water a circular motion.

  2) The effect of a wave on the shore depends on its height. Wave height is affected by the wind speed and the fetch of the wave. A high wind speed and a long fetch create higher and more powerful waves.

  3) As waves approach the shore they break. Friction with the sea bed slows the bottom of waves and makes their motion more elliptical. The crest of the waves rises up and then collapses.
• Constructive waves


  - Have a low frequency of 6-8 minutes.

  - They are low and long which gives them a more elliptical cross profile.

  - They have a powerful swash and weak backwash so build up beaches.

  
• Destructive waves


  - High and steep, a more circular cross profile.

  - Higher frequency of 10-14 waves per minute.

  - They have a strong backwash and a weak swash, which removes material from the beach.

  
• Tides


  - The periodic rise and fall of the ocean surface, caused by the gravitational pull of the moon and sun.

  - Tides affect the position at which waves break on the beach (at the high tide they break higher up the shore). The area of land between maximum high tide and minimum low tide is where most landforms are created and destroyed.
• Spring tides


  tides that have the greastest tidal range due to the alignment of the earth-moon-sun system
• Currents


  1) A current is the general flow of water in one direction - it can be caused by wind or by variations in water temp or salinity.

  2) Current move material along the coast.
• High energy coastlines


  - Receives high inputs of energy from large, powerful waves. These can be caused by strong winds, long fetches and steeply shelving offshore zones.

  - High energy coastlines tend to have sandy coves and rocky landforms eg. cliffs, caves, arches and stacks.

  - The rate of erosion is often higher than rate of deposition.
• Low energy coastlines.


  - Receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds, short fetches and gently sloping offshore zones.

  - Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of waves.

  - Low energy coastlines often have salt marshes and mudflats.

  - The rate of deposition is often higher than the rate of erosion.
• Sediment sources into the coastal system

  - Rivers carry eroded sediment into the coastal system from inland.

  - Sea level rise can flood river valleys, forming estuaries. Sediment in the estuary becomes part of the coastal system.

  - Sediment is eroded from cliffs by waves, weathering and landslides.

  - Sediment can be formed from the crushed shells of marine organisms.
• Sediment budget


  The difference between the amount of sediment that enters the system and the amount that leaves the system, is the sediment budget.

  - If more sediment enters than leaves, it's a positive sediment budget and an overall the coastline builds outwards.

  - If more sediment leaves than enters, its a negative sediment budget, and overall the coastline retreats.
• Sediment cells


  - The coast is divided into sediment cells.

  - These are lengths of coastline (often between two headlands) that are entirely self contained for the movement of sediment.

  - This means that processes going on in one cell doesn't affect the movement of sediment in another cell - each cell is a closed coastal system.
• Corrasion (erosion)


  Rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits of and smoothing surfaces.

  
• Hydraulic action (erosion)


  Air in cracks of cliffs is compresses, when waves crash in, the pressure is exerted by the compressed air It breaks of rock pieces.

  
• Cavitation (erosion)


  As waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off.
• Wave quarrying (erosion)


  The sheer energy of the waves as it breaks against a cliff is enough to detach bits of rock.
• Solution (erosion)


  Soluble rocks eg. limestone and chalk. get gradually dissolved by the seawater.
• Attrition (erosion)


  Bits of rock in the water smash against each other and break into smaller bits.

  
• Solution (transportation)


  - Substances that can dissolve are carries along in the water eg. limestone is dissolved into water that is slightly acidic.

  
• Saltation (transportation)


  - Larger particles such as pebbles or gravel, that are too heavy to be carried in suspension. Bounce along the sea bed because of the force of the water.

  
• Suspension (transportation)


  Very fine material are carried along in the water.

  
• Traction (transportation)


  Very large particles eg. boulders, are pushed along the sea bed by the force of the water.

  
• longshore drift


  Transports sediment along the shore.

  1) Swash carries sediment up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline.

  2) when there's an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline.

  
• Deposition


  When material being transported is deposited onto the coast.
• Marine deposition


  sediment carried by seawater is dropped.
• Aeolian deposition


  When sediment carried by wind is deposited
• Why does deposition occur?

  When the sediment load exceeds the ability of the water or wind to carry it. This can be because sediment load increases eg. landslide.

  Or because wind / water flows slow down:

  1) Friction increases- If waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases, which slows down water or wind.

  2) Flow becomes turbulent - If water or wind encounters an obstacle eg. area of vegetation or a current moving in the opposite direction) flow becomes rougher and overall speed decreases.

  3) If wind drops, wave height, speed and energy will decrease as well.
• Salt weathering


  1) Caused by saline water.

  2) Saline water enters the pores and cracks in rocks at high tide.

  3) As the tide goes out the rocks dry and water evaporates forming salt crystals, these expand, exerting pressure on the rock and so pieces fall off.

  
• Freeze-thaw weathering


  1) Occurs where temperatures fluctuate above and below freezing.

  2) Water enters the joints and cracks in a rock.

  3) If the temp drops below freezing, water in the cracks freeze and expand.

  4) Over time, repeated freeze thaw action weakens the rock and causes pieces to fall off.

  
• Wetting and drying


  1. Some rocks contain clay.

  2. When clay gets wet, it expands and the pressure caused by this breaks fragments off the rock.

  
• Chemical weathering


  1) The breakdown of rock by changing its chemical composition.

  2) For example, carbon dioxide in the atmosphere dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rock that contains calcium carbonate, so rocks are gradually dissolved.

  
• Biological weathering


  Plant roots can get into small cracks in the rock.

  As the roots grow, the cracks become larger.

  This causes small pieces of rock to break away.

  
• massmovement


  The shifting of material downhill due to gravity. In coastal areas it is most likely to occur when cliffs are undercut by wave action. This causes an unsupported overhang, which is likely to collapse.
• Slides


  Material shifts in a straight line