Coasts

• Mechanical weathering
• The breakdown of rock without changing its chemical composition
• Freeze-thraw weathering-
• when the temperature above or below 0 degrees (the freezing point of water)
• Water freezes - expands and puts pressure on the rock
• Water thraws - contracts and releases the pressure on the rock
• Repeated freezing and thrawing widens the cracks - casues the rock to break up

Chemical weathering

• Breakdown of rock by changing its chemical composition
• Carbonation weathering-
• happens in warm and wet conditions
• rainwater has carbon dioxide dissolved in it - weak carbonic acid
• carbonic acid reacts with rock that contains calcium carbonate

Hydraulic power

• Waves crash against rock and compresses the air in the cracks - puts pressure on the rock
• Repeated compression - widens the cracks and makes bits of rock break off

Abrasion

• Eroded particles in the water scrape against rock - removes small pieces

Attrition

• Eroded particles in the water smash into each other and break into smaller fragments
• Their edges also get rounded off as they rub together

Solution

• Weak carbonic acid in sea water dissolves rock like chalk and limeston

• The waves that carry out erosional processes are called destructive waves

• Destructive waves have a high frequency (10-14 waves per minute)

• They're high and steep
• Their backwash is more powerful than their swash - material is removed from the coast

Cliff retreat

• Waves cause the most erosion at the foot of a cliff - forms a wave-cut notch (erosion makes it unstable over time)
• The part of the cliff above sea level is also affected by mechanical and chemical weathering - makes the cliff unstable and collapse
• The collasped material is washed away and a new wave-cut notch starts to form
• Repeated collapsing results in the cliff retreating
• The rate of retreat depends on lots of things;
• geology - soft rock retreats quickly and hard rock can be eroded over thousands of years
• vegetation - cliffs covered in vegetationa are more stable and retreat slowly
• Ciff collapses are mass movements - happen when the force of gravity acting on a slope is greater than the force supporting it
• 3 types of mass movements;
• Slides - material shifts in a straight line
• Slumps - material shifts with a rotation
• Rockfalls - Material shifts vertically

• Headlands and Bays form where there are alternating bands of resistant and less resistant rock along a coast
• The less resistant rock (e.g. clay) is eroded away quickly - forms a bay (have a gentle slope)
• The resistant rock (e.g. chalk) is eroded away more slowly - forms a headland (steep sides)
• For example, the Foreland and Swanage Bay in Dorset