Landforms of coastal erosion

Question 1

How do C.A.S.S form?

Answer 1

1. At pinnacle headlands, faults are eroded by hydraulic action and abrasion to create small caves.
2. The overlying rock in the cave may collapse, forming a blowhole. Water spurts out of the blowhole when a wave enters at the base of the headlands, forcing sea spray and air out of the top of the headland
3. Marine erosion widens faults in the base of the headland, widening over time to create a large cave.
4. The cave widens due to erosion and sub-aerial processes, eroding through to the other side of the headland, forming an arch.
5. The arch widens until the top of it becomes unstable and collapses by
   mass movement, leaving a stack (a side of the arch is disconnected from the mainland.
6. Marine erosion (wave energy) attacks the base of the stack so it collapses into a stump
7. A wave cut platform remains, exposed at low tide and covered at high tide.

Question 2

How is a wave-cut notch formed?

Answer 2

1. Destructive waves are mostly concentrated around the high-tide line so cliff erosion occurs by hydraulic action and corrasion to form a wave cut notch at the base of the cliff.

Question 3

How is a wave-cut platform formed?

Answer 3

1. A wave cut notch forms
2. As the notch becomes deeper and sub-aerial processes weaken the top of the cliff, the cliff face becomes unstable and collapses by mass movement
3. A platform of the unaffected cliff base forms beneath the wave-cut notch
4. The marine erosion continues (the cliff retreats and collapses) forming a wave-cut platform exposed at high-tide.

Question 4

How do headlands and bays form? What other way can they form?

Answer 4

1. At a discordant coastline, less resistant rocks are eroded at a faster rate than more resistant rocks, forming headlands. The areas where the soft rock has eroded away, next to the headland, are called bays
2. These headlands experience wave refraction and the bays experience low-energy waves.
3. At a concordant coastline, differential erosion can take place where there is a weakness within the first layers of rock, forming headlands and a bay.

Question 5

What are geos?

Answer 5

Linear inlets in a sea cliff that form as the sea erodes along a a line of weakness

Question 6

What factors determine whether a geo will form?

Answer 6

• bedding planes
• fissures/cracks/joints

Question 7

What is a blowhole?

Answer 7

A sea cave that has grown inwards and upwards in a headland.

Question 8

How do blowholes form?

Answer 8

Vertical erosion of a cave continues upwards, this can be extended to the top of the cliff due to a vertical line of weakness.