Costal landscapes in the UK

• Weathering is the breakdown of rocks in situ
• Erosion is when rocks are broken down and carried away by something, e.g. seawater
• Mechanical weathering is the breakdown of rock without changing its chemical composition.
• Mechanical weathering: freeze-thaw weathering:

  • Happens when the temperature alternates above and below 0
  • Water enters rock that has cracks
  • When the water freezes it expands, which puts pressure on the rock
  • When the water thaws it contracts, which releases the pressure on the rock
  • Repeated freezing and thawing widens the cracks and causes the rock to break up
• Chemical weathering is the breakdown of rock by changing its chemical composition.
• Chemical weathering: Carbonation:

  Happens in warm and wet conditions

  • Rainwater has carbon dioxide dissolved in it, which makes it a weak carbonic acid
  • Carbonic acid reacts with rock that contains calcium carbonate, e.g. carboniferous limestone, so the rocks are dissolved by the water
• Mass movement is the shifting of rocks and loose material down a slope, e.g. a cliff

  • Happens when the force of gravity acting on a slope is greater than the force supporting it
  • Causes the coast to retreat rapidly
  • It's more likely to happen when the material is full of water - water acts as a lubricant, and makes the material heavier
  • When a material shifts, it can create a scarp (a steep 'cut' in the side of the slope)
• Mass movement: Slides:

  Material shifts in a straight line along a slide plane

  
• Mass movement: Slumps:

  Material rotates along a curved slip plane

  
• Mass movement: Rockfalls:

  Material breaks up, often along bedding planes, and falls down a slope

  
• Waves:

  • When wind blows over the surface of the sea it creates waves
  • The stronger the wind, the longer the wind has been blowing and the greater the fetch (the distance the wind blows over the sea), the more powerful the wave
  • Storms can create storm surges - temporary sea level rises caused as strong winds push water onshore
• Destructive waves:

  • Erode the coast
  • High frequency
  • High and steep
  • Backwash (water moving down the beach) is more powerful than their swash (water moving up the beach), so material is removed
• Constructive waves:

  • Deposit material
  • Low frequency
  • Low and long
  • Their swash is more powerful than their backwash, so material is deposited
• Erosion: Hydraulic power:

  Waves crash against rock and compress air in the cracks. This puts pressure on the rock. Repeated compression widens the cracks and causes bits of rock to break off
• Erosion: Abrasion:

  Eroded particles in the water scrape and rub against rock, removing small pieces
• Erosion: Attrition:

  Eroded particles in the water collide, break into smaller pieces and become more rounded
• Longshore drift:

  • Waves follow the direction of the prevailing wind
  • They usually hit the coast at an oblique angle (any angle that isn't a right angle)
  • The swash carries material up the beach, in the same direction as the waves
  • The backwash then carries material down the beach at right angles, back toward the sea
  • Over time, material zigzags along the coast

  
• Deposition:

  • Occurs when water carrying sediment loses energy and slows down
  • Coasts build up when the amount of deposition is greater than the amount of erosion
  • The amount of material that's deposited on an area of coast is increased when:
  • There's lots of erosion elsewhere on the coast (so more material is available)
  • Lots of material is transported into the area
  • Constructive waves drop more material than they remove - there's more deposition than erosion