Coasts

• How do waves form?

  they form when thewind blows over the sea. Friction with the surface of the water causes small ripples in the water, which develop in to waves.
• What is the Fetch?

  The distance the wave blows across
• How does the fetch affect the wave?

  The longer the fetch the more powerful the wave
• Trough:

  the base of the wave
• Swash:

  when the wave breaks the water that is washed up onto the beacj
• Backwash:

  The water that runs back down the beach
• Crest:

  The highest point of the wave
• What happens when the waves reach the coast?

  despite the relatively wavy surface in the ocean, there is little horizontal movement of water. This only occurs when the waves break and surge up the beach as they approach the shore. As the water gets shallower, the seabed interrupts the circular motion of the water making the waves more elliptical. This causes the crest of the wave to rise up and eventually collapse on the beach.
• Characteristics of destructive waves:

  • created in stormy conditions
  • created from big, strong waves when the wind is powerful and has been blowing for a long time
  • occurs when the wave has lots of energy and the wave has travelled over a long fetch
  • short wave length, high and steep
  • stronger backwash than swash
  • tend to erode the coast
  • high frequency (10-14 a min)
• Characteristics of constructive waves:

  • created in calm weather
  • less powerful than destructive waves
  • swash is stronger than the backwash
  • longer wavelength and shorter height
  • break on shore depositing material, building up beaches
  • low frequency (< 10 a min)
• Coast:

  where the land meets the sea
• Beach:

  large areas of sand and pebbles deposited by the sea
• Bay:

  a part of the coastline that has been deeply eroded by the sea
• Headland:

  an area of higher land that points out to sea
• Cliff:

  Steep rock wall that faces out to sea
• Mechanical weathering:

  The disintegration of rocks. Where this happens, piles of rock fragments called scree can be found at the foot of cliffs
• Chemical weathering:

  Caused by chemical changes, rainwater, which is slightly acidic, very slowly dissolves certain types of rocks and minerals
• Biological weathering:

  Due to actions of flora and fauna, plant roots grow in crack in rocks, animals such as rabbits burrow into weak rocks such as sandstone
• Freeze-thaw weathering:

  • water collects I cracks and holes (pores) in the rock
  • at night this water freezes and expands, making the cracks in the rocks bigger
  • when the temperature rises and the ice thaws, water will seep deeper into the rock
  • after repeated freezing and thawing, fragments of the rock may break off and fall to the foot of the cliff
• Salt weathering:

  • seawater contains salt, when the water evaporates It leaves behind salt crystals
  • the slat crystals grow and expand in cracks and holes
  • this puts pressure on the rocks and flakes m ay eventually break off
• Scree:

  fragments of rock the that have broken off in weathering processes and fallen to the foot of a cliff
• Carbonation:

  • rainwater absorbs carbon dioxide form the air and becomes slightly acidic
  • contact with alkaline rocks such as chalk and limestone produces a chemical reaction causing the rocks to slowly dissolve
• The rate of erosion will be higher if:

  The coastline is exposed to a large fetch, such as the needles on the Isle of Wight, which has an 800km fetch across the Atlantic Ocean

  Strong winds blow for a long time and create destructive waves, these conditions are common in winter

  An area has no beach to act as a buffer between the sea and the cliffs
• Longshore drift:

  the movement of sediments along a coast by waves that approach at an angle to the shore but then the swash recedes directly away from it