Coastal Erosion

Coastal Erosion

Weathering
1. Mechanical weathering
  1. Mechanical weathering is the breakdown of rock without changing it chemical composition
  2. Freeze-thaw weathering
    1. It happens when the temperature alternates above and below 0 degrees, (freezing point of water
    2. 1) Water gets into the rock that have cracks in it
    3. 2) The water then freezes and expands, which puts pressure on the rock
    4. 3) The water then thaws and contracts, which releases the pressure
    5. 4) Repeated freezing and thawing widens the crack and causes the rock to break up
2. Chemical Weathering
  1. Chemical weathering is the breakdown of rock by changing its chemical composition.
  2. Carbonation weathering
    1. carbonation weathering happens in warm and wet conditions
    2. !) Rainwater has carbon dioxide in it, which makes it a weak carbonic acid
    3. 2) Carbonic acid reacts with rock that contains calcium carbonate, for example carboniferous limestone
Mass Movement
1. Mass movement is the shifting of rocks and loose material down a slope e.g. a cliff.
2. Mass movement happens when the force of gravity acting on a slope is greater than the force of supporting it.
  1. This causes the coast to retreat rapidly
3. It is more likely to happen when the material is full of water (saturated) - this acts as a lubricant
4. Types of Mass Movement
  1. Slides: material shift in a straight line
  2. Slumps: Material shifts with a rotation
Waves
1. Destructive waves
  1. They carry out erosional processes
  2. They have a high frequency (10-14 waves per minute)
  3. They are high and steep
  4. Their backwash is more powerful than the swash, this means the material removed from the coast
    1. backwash: the movement of water back down the beach
    2. swash: the movement of water up the beach
2. Constructive waves
  1. They have a low frequency (6-8 waves per minute)
  2. They are low and long
  3. Their swash is powerful and it carries material up the coast
    1. swash: the movement of water up the beach
  4. The backwash is weaker and it doesn't take a lot of material back down the coast, this means material is deposited along the coast
    1. backwash: the movement of water back down the beach
Processes of erosion
1. Hydraulic power
  1. waves crash against rock and compress the air in the cracks. This puts pressure on the rock. Repeated compression widens the cracks and makes bits of rock break off
2. Abrasion
  1. eroded particles in the water scrape and rub against rock, removing small pieces.
3. Attrition
  1. eroded particles in the water smash into each other and break into smaller fragments. Their edges also get rounded off as they rub together
4. Solution
  1. weak carbonic acid in seawater dissolves rock like chalk and limestone
Coastal Erosion Landforms
1. Wave-cut platforms
  1. 1) waves cause most erosion at the foot of a cliff 2) This forms a wave-cut notch, which is enlarged as erosion continues 3) The rock above the notch becomes unstable and eventually collapses 4) The collapsed material is washed away and a anew wave-cut notch starts to form 5) Repeated collapsing results in cliff retreat 6) A wave-cut platform is the platform is the platform that is left behind
2. Headlands and Bays
  1. Some rocks are more resistant than others
  2. Alternating bands of hard and soft rock are eroded leaving headlands and bays
  3. less resistant rock is eroded faster
    1. bays are sandy and are found where constructive waves are
3. Caves, Arches and Stacks
  1. 1) Headlands are usually made from resistant rock that have weaknesses like cracks 2) Waves crash into the headlands and enlarge the cracks - mainly by hydraulic power and abrasion 3) Repeated erosion and enlargment of the cracks causes a cave to form 4) Continued erosion deepens the cave until it breaks through the headland - forming and arch 5) Erosion continues to wear away the rock supporting the arch, until it eventually collapses 6) This forms a stack - an isolated rock that's seperate from the headland.
  2. Caves: caves occur when waves force their way into cracks in the cliff face. The water contains sand ans other materials that grind away the rock until the cracks become a cave.
    1. Hydraulic action is the predominant process
  3. Arches: If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
  4. Stacks: The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.

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	Created by izzylangley about 10 years ago