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- Coasts: weathering, mass movement and geology
Coasts: weathering, mass movement and geology
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Waves are not the only force shaping the coast. Weathering, mass movement and the rocks themselves all matter.
Weathering and mass movement
Weathering breaks rock down where it is.
Mechanical: freeze-thaw, when water in cracks freezes, expands and widens the crack.
Chemical: rainwater is a weak acid and slowly dissolves chalk and limestone.
Biological: plant roots and burrowing animals break rock apart.
Mass movement is rock or soil moving downhill under gravity. Sliding is a sudden movement along a flat surface. Slumping happens when soft cliffs such as clay become saturated and slip down a curved surface.
Mechanical: freeze-thaw, when water in cracks freezes, expands and widens the crack.
Chemical: rainwater is a weak acid and slowly dissolves chalk and limestone.
Biological: plant roots and burrowing animals break rock apart.
Mass movement is rock or soil moving downhill under gravity. Sliding is a sudden movement along a flat surface. Slumping happens when soft cliffs such as clay become saturated and slip down a curved surface.
Geology: concordant and discordant
A concordant coast has bands of rock running parallel to the coastline, as at Lulworth Cove in Dorset, where the sea broke through hard limestone and scooped out the softer rock behind.
A discordant coast has bands of rock at right angles to the coastline. Soft rock erodes into bays and hard rock is left as headlands, as at Swanage Bay and the chalk of Old Harry Rocks in Dorset.
Joints and faults are lines of weakness that the sea erodes first.
A discordant coast has bands of rock at right angles to the coastline. Soft rock erodes into bays and hard rock is left as headlands, as at Swanage Bay and the chalk of Old Harry Rocks in Dorset.
Joints and faults are lines of weakness that the sea erodes first.
Waves and weather
Destructive waves are tall and frequent with a strong backwash: they erode.
Constructive waves are low with a strong swash: they deposit.
The UK's prevailing wind is from the south-west, so south-west facing coasts get the biggest waves. Storms are most frequent in winter, so most erosion happens then.
Constructive waves are low with a strong swash: they deposit.
The UK's prevailing wind is from the south-west, so south-west facing coasts get the biggest waves. Storms are most frequent in winter, so most erosion happens then.
Explain why a discordant coast has headlands and bays.
- The bands of rock meet the sea at right angles.
- Soft rock, such as clay, erodes quickly and forms bays.
- Hard rock, such as chalk, resists erosion and is left sticking out as headlands.
Answer: Differential erosion: soft rock forms bays, hard rock forms headlands.
Weathering breaks rock in place; mass movement moves it downhill. Discordant coasts (rock at right angles to the sea) form headlands and bays; concordant coasts (rock parallel) form coves. Winter storms from the south-west cause most erosion.
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