Lithosphere (coastal)

Question 1

Coastal processes of erosion

Answer 1

1. Hydraulic action — pounding waves compress trapped air in the rocks, creating an explosive blast which weakens and loosens rock fragments.
2. Abrasion/corrasion — rock fragments thrown against the headland create a sandblasting (abrasive) action, wearing away the rock.
3. Solution/corrosion — carbonic acid in sea water weathering limestone and chalk.
4. Attrition — rock fragments slowly being ground down by friction from wave action into smaller and rounder pieces to form sand.

Question 2

Wave cut platform

Answer 2

1. Weaknesses such as joints, faults or cracks in cliffs are undercut by erosion to form a wave-cut notch.
2. Coastal erosion
3. The rock above overhangs over the notch and, as erosion continues, the notch enlarges until the unsupported overhang collapses due to the weight.
4. The new cliff face is then eroded and through time, the cliff retreats inland, leaving a gently-sloping rocky surface called a wave-cut platform, which extends out to sea away from the cliff.
5. The platform is abraded by rock materials, with rock pools and pot holes forming, evident at low tide.
6. Eg. Seven Sisters.

Question 3

Headland and bay

Answer 3

1. Formed by differential erosion, where softer, less resistant rocks erodes
2. more quickly than harder, more resistant rocks.
3. Coastal erosion
4. A headland is an area of hard rock which juts out into the sea and a bay is a sheltered area of softer rock between headlands.
5. Often form in areas with a discordant coastline where alternate bands of rock are found at right angles to the coast.
6. Constructive waves build a small beach in the sheltered bay between the headlands.
7. Eg. Lulworth Cove.

Question 4

Stacks

Answer 4

1. Coastal erosion
2. Rocks contain weak points that are more easily eroded.
3. Over time, lines of weakness are enlarged and develop into small sea caves.
4. In some cases, a blowhole can form in the roof of the cave as compressed air is pushed upwards by the power of the waves, causing vertical erosion.
5. There may be erosion on both sides of the headland due to wave refraction until eventually the sea cuts through the back walls of the caves, forming an arch.
6. Continued erosion enlarges the arch.
7. The base of the arch is also undercut by the erosion, causing the arch to become unsupported.
8. Eventually the arch collapses due gravity to form a stack.
9. Eg. Old Harry.

Question 5

Sand spit

Answer 5

1. Sand spits are formed by the process of longshore drift.
2. Swash is where waves, driven by prevailing wind push material up the beach at an angle.
3. The returning backwash is dragged back by gravity down the beach at right angles.
4. Spits form when there is a change in direction on a coastline allowing a sheltered area for deposition.
5. Material slowly builds up to appear above the water.
6. The spit develops as long as the supply of deposits is greater than the amount of erosion.
7. The shape can become hooked or curved at the end in response to changes in wind direction/currents.
8. A salt marsh may form in a sheltered area behind a sand spit.
9. Eg. Spurn Head.

Question 6

Sand bar

Answer 6

1. Sand spit
2. A sand bar is formed when a spit grows across the entrance to a bay, connecting two headlands, enclosing a sheltered lagoon behind it.
3. This happens when there is no strong flow of water from a river into the sea and through time, this stagnant lagoon water is infilled by deposition.
4. Bars form when there is a change in direction on a coastline, which allows a sheltered area for deposition.

Question 7

Tombolo

Answer 7

1. Sand spit.
2. A tombolo is formed when a spit extends out from the mainland, connecting to an island .
3. Eg. St Ninian’s Isle