2B.4 How do waves shape the coast? (erosion)

how does cliff retreat to form wave cut platforms and wave cut notches? 8 steps

1. a wave cut is a small indent at the base of a cliff formed when a cliff is undercut by the sea 2. when a wave breaks on a cliff, all of the waves energy is concentrated one one specific point and this section of the cliff experiences more rapid erosion via corrosion, hydraulic action and attrition as the notch is attacked 3. this eventually leads to the formation of a wave cut notch, where the cliff has been undercut 4. as the cliff has been undercut, the section of the cliff above the notch (the overhanging rock) no longer has any support and will eventually collapse 5. the repeated process of the collapse of the cliff and then the undercutting of the cliff is often referred to as the 'retreat' of the cliff 6. as the cliff retreats, a gentle platform (with a shallow gradient of <5), referred to as a wave cut platform is left behind- this platform is heavily scarred by erosion from the transportation of rock across it and is inundated at high tide 7. as the platform grows, the waves have to travel further to reach the cliff and they'll lose more and more of their energy 8. once the platform reaches a certain size, the waves will have too little energy by the time they reach the cliff to undercut it and so there is a physical limit on the size a wave cut platform can be

how do landforms of erosion form by wave action: cave arch, stack stump?

1. the headland protrudes in the sea as it is more resistant 2. this means wave energy is concentrated on it due to wave refraction 3. wave action attacks weaknesses in the headland (joints, faults and cracks) due to abrasion and hydraulic action (the force of the water compressing pockets of air leading to cavitation) 4. this widens cracks into crevices and then caves 5. hydraulic action and abrasion continue especially during winter storms which produce destructive waves 6. caves can be eroded to form blowholes as the ceiling collapses 7. if caves are eroded through, an arch is created. Erosion continues and the top of the arch becomes unstable 8. if caves are eroded through, an arch is created. Erosion continues and the top of the arch becomes unstable 9. this eventually collapses to produce a stack e.g. Old Harry, Purbeck, Dorset and a stump like Old Harry's Wife

what is solution? (corrosion)

Carbonate rocks react with weak acids in rainwater and seawater. This slowly dissolves them

what is abrasion? (corrasion)

Sediment picked up by the waves and thrown at the cliff. This grinds/ scrapes against the cliff like sand paper, wearing it down. Perhaps the most effective wave erosion process

what is hydraulic action?

air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face. When the wave retreats, pressure is released explosively (cavitation). This can widen cracks and dislodge blocks from the cliff face

what does a cliffs morphology depend upon?

cliffs vary in their morphology depending on lithology and whether they are actively eroded by wave action or they are affected by sub-aerial processes

what is the effect of hydraulic action on lithology?

heavily jointed sedimentary rocks are most vulnerable. Areas with more weaknesses next to areas with less can result in differential erosion

what are the four types of erosion?

hydraulic action (wave quarrying) abrasion (corrassion) attrition solution (corrosion)

what is the effect or solution (corrosion) on lithology?

limestone and chalk are carbonate rocks that are vulnerable

what is the effect of attrition on lithology?

softer sediment is broken down quicker

what is the effect of abrasion on lithology?

there needs to be loose sediment available to cause this. Soft sedimentary rocks like sand and unconsolidated rocks are most vulnerable

what is attrition?

this works on loose sediment already eroded from a cliff. sediment gets smaller and more rounded (abrasion taking place too)