booklet 7 - landscapes

• wave cut platform


  - flat rock surface exposed at low tide, extending out to sea to form cliff base

  
• wave cut platform - formation

  - erosion between high tide line and low tide line form wave cut notch

  - notch deepens further until cliff is formed, repeats and the cliff retreats

  - overlying material eroded, rock below low tide mark doesn't, it stays flat forming a wave cut platform
• Why do wave-cut platforms rarely extend for more than a few hundred metres?

  because the notch becomes unstable and collapses
• wave cut platform - negative feedback

  - wave energy dissipates the wider the wave cut platform

  - erosive power of cliff base declines + rate of retreat slows

  - change in inputs can induce system and result in more rapid cliff erosion again
• wave cut platform - INPUTS

  - wave energy

  - sea level

  - tidal range
• wave cut platforms - PROCESSES

  - weathering

  - erosion

  - hydraulic action

  - abrasion
• wave cut platforms - OUTPUTS

  - material from cliff collapse
• most dominant process in formation of wave cut platform

  - erosion

  - as the platform cant form without the formation of a notch which occurs through the waves eroding the coastline
• examples of wave cut platforms

  Worms Head - The Gower, Swansea

  --- formed with limestone

  Cape of Good Hope - South Africa

  --- formed with sandstone
• geo

  - a gully, inlet or narrow + deep cleft in face of cliff

  - common on coastline of Shetland and Orkney Islands

  - created by wave driven erosion of cliffs along faults and bedding planes in rock
• caves arch stacks and stumps

  
• caves, arch, stacks, stumps - formation

  - cracks exposed through hydraulic action pressurizing air, forcing cracks to widen

  - these widen overtime + form wave- cut notches

  - wave refraction causes waves to concentrate energy on sides, deepens caves

  - wave cut notches widen base of arch, joints exposed and blowholes may form

  - arch becomes unstable and collapses, forms stack

  - stack eroded further, weakens through subaerial processes

  - stack collapses to form stump, material transported + deposited
• caves, arch, stacks, stumps - INPUTS

  - cracks within headland
• caves, arch, stacks, stumps - PROCESSES

  - hydraulic action

  - wave refraction

  - weathering

  - abrasion
• caves, arch, stacks, stumps - OUTPUTS

  - wave cut notch

  - cave

  - arch

  - stack

  - stump
• most dominant process in formation of caves, stacks, stumps and arch

  - hydraulic action

  - because this is what causes crack to initially widen

  - also helps to erode caves, creating wave cut notches + weaken headland
• caves, arch, stacks + stumps - examples

  old Harry Rocks - Jurassic coast, Dorset

  --- formed with chalk

  The Twelve Apostles - mainland Australia

  --- formed with limestone
• formation of bays and headlands

  - form when less resistant rock retreats (forming bay) and more resistant rock is left behind (headland)

  
• where are bays and headlands found?

  - on discordant coastlines

  - headlands more vulnerable to forces of erosion as are more exposed to powerful waves

  - the bays are protected by headlands
• bays and headlands - examples

  Swanage Bay - Dorset

  --- Chalk and limestone

  San Francisco bay - California , USA

  --- clay, Franciscan rock
• what is a cove?

  A wide, circular bay with a narrow entrance
• coves


  example - Lulworth Cove

  
• how do coves form on concordant coastlines?

  - occur when bands of differing rocks run parallel to each other

  - outer hard provides a protective barrier to erosion of the softer rocks further inland

  - sometimes outer hard rock is punctured, allowing sea to erode softer rock behind

  - creates a cove
• where is it that steep cliffs are likely to occur?

  - where rock is strong and resistant to erosion

  - sedimentary rocks that are dipping steeply or even vertically tend to produce steep and dramatic cliffs
• where is it that gentle cliffs are likely to occur?

  - usually reflect weak or unconsolidated rocks that are prone to slumping

  - a sheltered location w low energy waves and a short fetch
• what factors determine the rate of cliff retreat?

  marine factors

  - wave energy

  - fetch

  - presence of beach

  terrestrial factors

  - rock geology

  - lithology

  - subaerial processes

  other factors include

  - rising sea levels

  - human activities
• what is coastal morphology?

  - Shape and form of coastal landscapes and features

  - related to underlying geology, rock tyre and lithology
• strata


  layers of rock
• bedding plains


  horizontal, natural breaks in strata, caused by gaps in time during periods of rock formation
• joints


  vertical fractures caused by contraction as sediments dry out or by earth movements during uplift
• folds


  formed by pressure during tectonic activity which makes rocks buckle and crumple
• faults


  formed when stress or pressure to which a rock is subjected, exceeds its internal strength
• dip


  refers to angle at which rock strata lie
• how do these factors influence rates of cliff retreat?

  there is a direct relationship between rock type, lithology and cliff profiles