Coasts

• How many destructive waves are there a minute?

  10-14
• How many constructive waves are there a minute?

  8-10
• Constructive Waves

  Swash is greater than backwash

  Builds up the beach

  Long low waves

  Shallow slope angle shoreline
• Destructive Waves

  Backwash is greater than swash

  Short high waves

  Erodes the coastline

  Steeper slope angle shoreline
• How high are destructive waves?

  Over 1 metre high
• How high are constructive waves?

  Less than 1 metre
• Attrition is when waves cause rocks and boulders on the beach to bump into each other and break into smaller particles
• Abrasion is caused by large waves hurling beach material against the cliffs which acts like sandpaper
• Hydraulic action is the force of the waves compressing air in cracks in a cliff
• Solution is when salts and other acids in seawater slowly dissolve a cliff
• A discordant coastline has alternating layers of hard and soft rock running at right angles to the coastline
• How are headlands and bays formed?

  Headlands and bays are found along discordant coastlines where the rock type varies. Wave erosion attacks the coast. Where the rock is weaker it erodes faster and a bay is made; where the rock is stronger it erodes more slowly creating a headland
• How are cliffs, wave cut notches and wave cut platforms formed?

  Waves hit the base of a cliff. At hightide they reach further up the cliff face. Erosion is concentrated at the base of the cliff. Overtime a wave cut notch is formed due to undercutting. The cliff face is weathered and the weight of the overlying rocks means that it lacks support and falls. The cliff face moves backwards and a wave cut platform is created where the cliff once stood
• Explain how longshore drift works

  The swash approaches the beach at an angle because of the prevailing wind direction. The backwash returns to the sea at a 90 degree angle to the beach due to gravity. This causes sediment to be slowly transported along the beach
• How are sand dunes formed?

  Embryo dunes form around obstacles e.g rocks. These become bigger ( foredunes and yellow dunes) and are stabilised by grasses growing through them. In time, rotting vegetation adds organic matter to the soil making it more fertile so a greater variety of plants begins to grow
• How are spits formed?

  Prevailing wind brings waves inland. Longshore drift moves the sand. The coastline changes directions due to a river mouth. Sand builds up across the river. The very end is pushed around by the waves. Soil from the river is dropped behind the spit creating a marshland. The spit will never cross the river due to the current.
• Bars are created when longshore drift moves sand across a bay leaving a lagoon
• Tombolos are spits that joins the mainland to an island
• What is the fetch of a wave?

  The distance a wave travels
• What is weathering?

  The breaking down of rocks in situ
• What is chemical weathering?

  When rainwater hits rock and eats it away due to a chemical reaction
• What is mechanical weathering?

  Breakdown of rocks into smaller pieces without changing their chemical composition.
• Mass movement is the downslope movement of rock, soil or mud under the influence of gravity
• Rotational slip is when material rotates backwards into the cliff face as it falls
• A concordant coastline has layers of hard and soft rock that running parallel to the coastline
• What natural processes contribute to the formation of caves, arches, stacks, and stumps?

  Hydraulic action and weathering processes
• How do large cracks in rock formations begin to form?

  They are enlarged by hydraulic action.
• What happens to a crack as it grows into a notch and then a cave?

  Destructive waves converge and erode the crack.
• Why do caves become larger over time?

  Wave refraction draws waves to all sides, allowing for back-to-back cave formation.
• What occurs when waves break through the back of a cave?

  Arches are formed, and the base is widened as notches develop.
• How does weathering affect the stability of an arch?

  Weathering, such as freeze-thaw, weakens the top of the arch, making it unstable.
• What happens to the top of the arch after it becomes unstable?

  It collapses.
• What is left after the top of the arch collapses?

  A pillar of detached rock called a stack.
• What occurs at the base of the stack over time?

  Notches form, making the stack unstable.
• What happens to the stack eventually?

  It falls into the sea, leaving a base called a stump.
• When is the stump typically visible?

  At low tide.
• Crack -> Cave -> Arch -> Stack -> Stump
• Sea walls prevent erosion and flooding by absorbing the wave energy. Recurve sea walls rotate the waves back into the sea

  1. Can destroy habitats ❌
  2. £5000 per metre ❌
  3. Can last may years ✅
  4. Gives people a sense of security ✅
• Groynes are fences placed at 90 degrees down the shoreline to stop longshore drift which builds up sediment on the shoreline

  1. quite cheap ✅
  2. Act as windbreaks ✅
  3. May make access to the beach difficult ❌
  4. Need regular maintainance ❌