Factors affecting erosion

  • Wave steepness: steeper waves are higher energy so can erode more – breaking point is also important, as if waves break at the foot of the cliff, they will erode more than waves which break further from the shore
  • Fetch: distance travelled by the wave determines how much energy it has, and therefore its erosive power
  • Sea depth: steeply shelving seabed creates higher and steeper waves, so they have more erosive power
  • Coastal configuration: if there are headlands, these will be subject to more erosion due to refraction of waves as they alter to fit the shape of the coastline
  • Beach presence: beaches absorb wave energy so act as protection for the cliffs against erosion – steep narrow beaches dissipate energy from flatter waves – wide beaches spread out wave energy do can dissipate high and rapid energy inputs – shingle beaches dissipate energy quicker as well because of friction and percolation through the sediment
  • Human activity: people contribute to the removal of material from beaches so increasing erosion’s effect – simultaneously, humans construct sea defences which acts as a protection against erosive power
  • Geology:
    • Lithology means the characteristics of rocks, and in particular the resistance to erosion and permeability
    • Differential erosion relies on the lithology – weaker rocks with more joints, like limestone
    • Structure and variation of rock affects erosion also – rock lying perpendicular creates very different coastline to rocks lying parallel
    • Dip in rocks is a big factor – angle at which the rock strata lie – homogenous (Seven Sisters in Sussex), horizontal beds (Shetland, Scotland), vertical beds (Jersey), seaward dipping (Pennington Point, Sidmouth), landward dipping (Pondfield Cove, Isle of Purbeck)


Concordant coastline: Lulworth

  • Coastal village in Dorset
  • Seawards rock is Portland limestone, then Purbeck limestone, clays, greensand and chalk
  • Surrounding the cove, there are not really any headlands and bays as the rock is consistently parallel
  • A cove exists – Portland limestone has exposed other rocks – following meltwater stage of last Ice Age, river ran across top of rock strata into the sea – eroded Portland limestone over time and process continued, eventually forming cove
  • Shape of Lulworth Cove formed partly due to wave diffraction – energy spread out as waves go through the cove entrance, so waves diffract and create unique shape of cove

Discordant coastline: Durlston Head

  • This is along the Dorset coastline – the stretch runs north from Durlston Head, made from Portland limestone (resistant) – Swanage Bay is weaker greensand – chalk outcrop of Old Harry Rocks (Ballard Point)