COASTAL LANDSCAPES

• Wave processes


  Waves are formed by the wind moving across the surface of the sea. Waves cause erosion, transportation and deposition along the coastline.
• Factors affecting wave power

  • Wind speed
  • Fetch - the distance over which the wind blows
• Faster wind and longer fetch

  Bigger waves
• Swash and backwash


  Waves break at the shoreline, the water moving up the shore is the swash, the water moving back down the shore is the backwash
• Constructive waves


  Have a strong swash and a weaker backwash, deposit sediment on the shore
• Destructive waves


  Have a weak swash and a stronger backwash, erode sediment from the shore
• Constructive waves happen in calm weather and during summer, destructive waves happen in poor weather and during winter
• Erosion processes


  1. Hydraulic action - sheer force of waves pounding the coast

  2. Compressed air - air trapped in cracks expands when wave retreats, breaking rock

  3. Abrasion - pebbles/rocks dashed against the coast

  4. Attrition - pebbles/stones rubbing against each other, becoming rounded

  5. Solution - seawater dissolving rock
• Longshore drift


  Waves approach the shore at an angle, swash carries material up the shore at an angle, backwash carries some material back down the beach at a right angle, causing sediment to move along the coast
• Deposition processes


  Waves lose energy when entering shallow water, entering a bay, crossing a wide beach, or entering a shallow beach with an angle less than 90 degrees
• The sea is moved by wind and forms waves. Stronger waves cause erosion, weaker waves cause deposition.
• Cliff


  A steep or vertical edge of the coast, formed by erosion
• Formation of cliffs and wave-cut platforms

  Destructive waves erode the cliff, forming a wave-cut notch at the base. Sediment from the notch is transported and deposited below low tide, forming a wave-built terrace. Corrosion causes the notch to enlarge, undermining the rocks above which eventually collapse to form a cliff.
• Headland


  An area of hard rock that juts out into the sea
• Bay


  An area eroded between two headlands, where there is a combination of soft and hard rock
• Formation of sea caves, arches, stacks and stumps

  Wave-cut notches are eroded in the base of headlands, forming sea caves over time. If erosion continues, the cave can cut through to the other side, forming a sea arch. If the roof of the arch collapses, a sea stack is formed. Over time, the sea stack will erode to form a sea stump.
• Blowhole


  A shaft that goes through the roof of a sea cave to the land surface above, formed by compressed air expanding and shattering the rock
• Beach


  A gently sloping area of sand and shingle on a coastline, between high tide and low tide, formed by deposition
• Sand dunes


  Large mounds of sand deposited at the back of a beach, beyond the high tide mark, formed by onshore winds trapping sand with vegetation
• Tombolo


  A narrow ridge of sand or shingle that joins an island to the mainland, formed by waves approaching the island from different directions and losing energy
• Sand dunes


  • Lighter than the wet sand and blows inland
  • Trapped by vegetation (marram grass) and builds up to form sand dunes
  • Marram grass is a thick, coarse grass that has deep roots and can tolerate the salty environment
  • Roots help bind the grains of sand together and prevent them blowing further inland
• Sand dune locations


  • Rosslare, Co. Wexford
  • Tramore, Co. Waterford
• Tombolo


  A narrow ridge of sand or shingle that joins an island to the mainland
• Tombolo formation


  1. Waves approach an island from different directions

  2. Waves cancel each other out and lose energy

  3. Deposition between the mainland and the island

  4. Over time, a long, narrow sand bar builds up, connecting the island to the mainland
• Sand spit


  A long, narrow beach of sand or shingle, connected to the mainland at one end and extending across a bay at the other end
• Sand spit formation


  1. Longshore drift transports sand and shingle along the coast in a zigzag pattern

  2. At a change in the coastline (e.g. a bay), the waves slow down and deposit sediment on the seabed

  3. Over time, this material builds up and rises above the sea to form a sand spit

  4. Longshore drift continues to move sediment along the coast, developing the spit into a sand bar and separating the bay from the sea to form a lagoon
• Sand spit and lagoon examples

  • Donegal golf course in Co. Donegal is a sand spit
  • Lady's Island Lake in Co. Wexford is a lagoon
• Constructive waves and longshore drift cause transportation and deposition on coasts, forming beaches, spits and tombolos
• Swash and backwash


  The movement of water up and down a beach
• How sand spits form

  Longshore drift transports sand and shingle along the coast
• Lagoon


  A salt lake separated from the sea by a sand bar or spit
• How tombolos form


  Waves approach an island from different directions, cancel each other out and lose energy, causing deposition between the mainland and the island
• Beaches on OS maps

  Shown as a thin line along the coast
• The sea is an important source of food, with fishing and fish farming providing food and jobs
• Oil, gas and offshore wind farms provide energy from the sea
• International trade depends on sea transport, e.g. through the Suez Canal
• Coastal areas are popular for tourism and recreation
• Increasing numbers of visitors to beaches

  Can damage sand dunes by walking on the marram grass
• Sewage discharged into the sea can seriously damage marine life
• Coastal defence measures


  • Groynes - concrete or wooden walls built at right angles to the sea to trap sediment
  • Rock armour/boulders - placed at the base of cliffs or sand dunes to reduce wave erosion
  • Sea walls - built at the back of beaches to protect coastal towns, sometimes curved to turn waves back
  • Gabions - wired cages containing stones, placed in front of sand dunes or at the back of a beach to absorb wave energy