2.1 Coastal Landforms - Erosional Landforms

Define Cliffs

Cliffs are steep or sloping rock faces, by which the shape depends on geology and wave energy

→ high-energy waves erode the cliff base more than low-energy waves

How do cliffs and wave-cut platforms form?

1. Waves attack the base at high-water mark, forming a wave-cut notch (knick-point)

2. Hydraulic action, abrasion and corrosion widen and deepen the notch

3. Continued undercutting makes the cliff unstable

4. The overhanging rock collapses due to the lack of support

5. Backwash removes the debris (remainders), leaving a wave-cut platform

6. Repeated collapse causes a cliff retreat (coastal retreat)

Define Discordant coastlines

A discordant coastline is where different types of rock lie at right angles to the sea

Define a bay

A bay is an inlet of the sea where the land curves inward, usually with a beach.

Where do headlands and bays take place?

Occur on a discordant coastline (an alternating hard rock and soft rock at right angles to waves)

How do Headlands and bays form?

1. Soft rock (clay) is eroded more quickly by wave action

2. Softer rock is therefore worn back to form a bay (backwards dent)

3. Hard rock (limestone) erodes more slowly

4. Therefore, resistant rock is left jutting out into the sea as a headland (remains outwards)

Describe a headlands appearance

• projects out to sea

• has cliffs along its sides

• is usually longer than it is wide

• has a geology of resistant rock

Describe a bays appearance

• a wide, open entrance from the sea

• a roughly semi-circular shape extending into the coastline (backwards)

• land that is lower than the headlands surrounding it

• a bay may or may not have a beach

How do caves, arches, stacks and stumps form?

1. As waves approach the coast, wave speed decreases

2. waves bend so crests become more parallel to the coast → causing wave refraction

3. Refraction concentrates wave energy on headlands

4. Hydraulic action, abrasion and corrosion exploit weaknesses (cracks)

5. Cracks widen to form a cave

5. Continued erosion enlarges cave until it breaks through, forming an arch

6. weathering from above and erosion at the base weaken the arch

8. the arch collapses, leaving a stack

9. the stack is undercut and weathered until it collapses into a stump

State the order of arches, caves, stumps and stacks

1. cave

2. arch

3. stack

4. stump