L2 - Purbeck Rocks Flashcards
What is a discordant coastline?
A coast where bands of hard and soft rock lie at right angles to the coastline forming headlands (hard rock cliffs) and bays (soft rock with beaches)
What is a concordant coastline?
A coast where the rock type runs parallel to the coastline
How does a cave form?
Destructive waves break against a headland (hard and resistant rock) (cliff) and joints/faults are attacked. Through hydraulic action and abrasion erosion occurs opening a crack to become wider and wider causing a cave.
How does an arch form?
When the wave hits the back of the cave, air is trapped within, compressed and at high pressure. When it is released erosion occurs.
Pebbles swirled around by the water causes abrasion eventually breaking through the back of the cave (headland) causing an arch.
How do stacks and stumps form?
Continual erosion at the base of the arch puts pressure on the weak roof, eventually causing it to collapse leaving 2 stacks.
Further weathering and erosion leaves smaller flatter versions of stacks called stumps.
Define the two types of weaknesses in rocks.
Joints - small vertical cracks found in rocks
Faults - larger cracks due to past tectonic movements where rocks have moved
How does a wave cut notch form?
Continual erosion at the base of the cliff through hydraulic action and abrasion causes a small notch to form as the cliff is undercut between high and low water marks.
How does a wave cut platform form?
As the wave cut notch forms the cliff is left with an overhang which is unsupported, therefore it falls creating a gentle slop by the base of the cliff called a wave cut platform.
Explain wave refraction.
- Waves are coming in to headlands and bays at the coastline
- The headlands are shallower than the bays
- The waves come in at parallel crests but as the wave hits the headland the crests bunch up with lots of energy
- This forces the rest of the waves on either side by the bays to bend (refract), with less energy as it is dissipated.
