Erosional Landscapes and Landforms

Cracks, Caves, Arches, Stacks & Stumps

• joint widens to form crack

• crack erodes to form cave

• caves eroded through into an arch

• unsupported rock in the arch collapses into stack

• weathering and erosion causes stack to become stump

Cliff Profiles

• Steep Cliffs = rock is strong and resistant to erosion, no beach, long fetch, high energy environment promotes steep cliff development

• Gentle Cliffs = weaker rocks, less resistant to erosion, prone to slumping, large beach reduces wave energy so prevents steep cliff from forming

• structure involves the disposition of rock and its bedding planes which

  determines its strength and the surface area exposed to wave erosion

  and subaerial processes

• structure involves the jointing of rocks which will also impact on

  surface area and the physical resistance of rocks to erosion

• lithology is the hardness or rock strength/make up

• rock hardness affects its resistance to wave processes

• lithology will also determine the porosity of rocks

Cliff Rate of Retreat

• Rate of Retreat = cliffs more likely to retreat if they’re made of soft unconsolidated rock

Negative Feedback Mechanisms can help protect and restore a coast. If the cliff collapses the material can protect the base from erosion, reducing further cliff recession.

Wave-Cut Notch Platform

Occurs at steep cliffs:

• erosion is concentrated around the high-tide line creating a wave-cut notch

• as the notch becomes deeper the cliff face becomes unstable and collapses

• leaves behind a platform of the unaffected cliff base

• backwash carries away debris and wave cut platform is left

Negative Feedback occurs as the length of the platform is limited because eventually the waves an no longer reach the cliff, reducing erosion. Act of erosion creating the wave-cut platform has directly decreased rate of erosion in the future.

Bays + Headlands

1. weakness in rock on concordant coastline (e.g. joint)

2. erosion widens joint into crack, then a cave, then an arch, then the arch collapses and waves erode soft rock left at the coastline

3. wave refraction around jutting out hard rock forms semicircular bay

4. bay stops either because it hits another band of hard rock or because waves have lost energy as bay is to deep

Raised Beach

• beach profile has shifted due to sea levels dropping or land rising

• beach becomes land and offshore, which was underwater before, becomes the beach and erosion acts on it

• vegetation succession occurs on raised beach that has become land

Concordant Coastline

layers of rock run parallel to the coastline

Discordant Coastline

layers of rock run perpendicular to the coastline