Coasts

• The coast is a narrow zone where the land meets the sea/ land and sea overlap.
• Discordant coastlines have layers of rock which run perpendicular to the coastline, therefore exposing different rock types.
• Concordant coastlines have layers of rock which run parallel to the coastline, therefore only exposing one type of rock.
• Sources of sediment in sediment cells: weathering and mass movement, rivers flowing into the sea (bring sand, silt, mud) rivers bring 90% of sediment in some sediment cells, estuaries, cliff erosion, offshore sand banks, marine organisms (coral, shells).
• Headlands and Bays

  • On a discordant coastline with different rock types exposed, the less resistant rock (e.g. clay) erodes first and retreats to form a bay
  • The more resistant rock (e.g. chalk) erodes slowly, leaving the rock sticking out at sea as a headland
  • A beach develops within the bay as the headlands help shelter the bay, offers protection from high energy waves, here the waves are constructive (low energy) which deposits material, the eroded soft rock (of bay) broken down by attrition providing material for the beach.
• Wave breaking/shoaling

  • individual water particles moves in circular motion, as we go deeper into the water the movement is less
  • eventually reach a point where water is not moving, deep water waves not interacting with sea bed (offshore)
  • water waves touching sea bed (inshore), when wave hits the seabed it creates friction
  • this slows down bottom of wave but top of the wave carries on moving the speed it was before → movement of water becomes "eliptical", more stretched out
  • This causes a shorter wave length and increased wave height.
• Beach formation

  1. Deposition occurs when accumulation of sand and shingle is faster than the removal

  2. Deposition occurs where there is low energy and a large supply of material (e.g. in bays due to wave refraction)
• Storm beaches

  • Built up by a strong swash during spring high tides
  • Consist of largest calibre material thrown up by the largest waves
  • Remain unmoved because subsequent tides cannot reach them
• Sand beaches

  • Gentle gradient (5 degrees)
  • Sand particles are small - this affects the swash and backwash to lead to a gentle beach
• Ridges and runnels

  • Occur at specific points for wave activity such as the mean turning points for low and high tides where the cycle goes from neap to spring
  • Run parallel to the shoreline
  • Broken by channels that drain water off the beach
  • Caused by strong backwash on sandy beaches
• Ridge and runnel systems are formed due to the interaction of tides, currents, sediments and the beach topography. They only form on beaches with a shallow gradient.
• Shingle beaches


  • Shingle beaches may make up the whole of the beach or just the upper part due to high spring tides
  • Steeper gradient (10 - 20 degrees)
  • Ridges are formed from lower tides as spring goes to neap
  • Built up from constructive waves with a strong swash
• Most mid latitude beaches undergo a cycle of erosion and deposition following the seasonal changes in wave action. During the winter, mid latitude storms are more vigorous producing more wave action and erosion. Hence, beaches tend to narrow during the winter. Wave action subsides during the summer as storms weaken somewhat favouring deposition over erosion and producing broader beaches.
• Cusps and ripples

  • Cusps are semi circular depressions when waves break on the beach and the swash and backwash are strong. It happens at the junction between the sand and shingle. Sides of the cusp channel the swash into the middle deepening it.
  • Ripples are developed by wave action or tidal currents
• Beaches can be:

  • swash aligned - swash is moved up and down the beach with little lateral transfer
  • drift aligned - sediment is transported along the coast by LSD.
• Tombolo

  • where a beach extends out to join an offshore island through longshore drift
  • e.g. Chesil beach in Dorset (30km long and 14m high) - Portland Island to the mainland
• Bar

  If a spit develops in a bay into which no major river flows, then it may build across the bay linking 2 headlands to form a bar. They trap water behind them to form a lagoon.
• Barrier Islands

  Coastlines paralleled by offshore narrow strips of sand dunes, salt marshes and beaches are known as barrier islands.
• Spits

  • long narrow accumulations of sand and/or shingle with one end joining to the mainland and another projecting out into the sea or extending partway across a river estuary.
  • they often have a hooked end due to the second prevailing wind, fetch, or wave refraction carrying some material into more sheltered waters.
• For a spit to be created there needs to be:

  1. LSD occurring
  2. shallow and sheltered water
  3. change in the shape of the coastline