coast

• Littoral zone


  The area of shoreline where land is subject to wave action
• Coastal zones


  • Offshore
  • Nearshore
  • Foreshore
  • Backshore
• Offshore


  The area of deeper water beyond the point at which waves begin to break, friction between the waves and the sea bed may cause some distortion of the wave shape
• Nearshore


  The area of shallow water beyond the low tide mark, within which friction between the seabed and waves distorts the wave sufficiently to cause it to break (breaker zone)
• Foreshore


  The area between the high tide and the low tide mark
• Backshore


  The area above the high tide mark, affected by wave action only during major storm events
• Ways to classify coasts

  • Long term criteria
  • Short term processes
• Geology


  Characteristics of land, including lithology (rock type) and structure (arrangement of rock units)
• Eustatic change


  A change in the volume of water in the ocean
• Isostatic change


  A change in the height of the land (tectonic processes)
• Energy inputs to coasts

  • Waves
  • Tides
  • Currents
  • Rivers
  • Atmospheric processes
  • Gravity
  • Tectonics
• Other categories used to classify coasts

  • Human activity
  • Landforms
  • Tectonics
• Coastal landscapes formed by the littoral zone

  • Rocky, cliffed coastline
  • Sandy coastline
  • Estuarine coastline
• Rocky, cliffed coastline


  Areas of high relief varying from a few metres to hundreds of metres in height, usually form in areas with resistant geology, in a high energy environment, where erosion is greater than deposition and destructive waves
• Sandy coastline


  Areas of low relief with sand dunes and beaches, that are much flatter, they usually form in areas with less resistant geology, a low energy environment, where deposition > erosion, and constructive waves
• Estuarine coastline


  Areas of low relief with salt marshes and mudflats (estuaries), they form in river mouths, where deposition > erosion, in a low energy environment, usually in areas of less resistant rock
• Types of coastlines


  • Concordant
  • Discordant
• Concordant coasts


  Where rock strata or folds run parallel to the coast, also known as Dalmatian coasts or Pacific coasts
• Discordant coasts


  Where rock strata or structures are aligned at an angle to the coastline, also known as Atlantic coasts
• Examples of concordant coasts

  • South Dorset coast
  • Dalmatian coast Croatia
  • Haff coastlines (Baltic Sea)
• Headlands and bays


  Characteristic of discordant coastlines, less-resistant rocks are eroded to form bays and the resistant rocks forms headlands
• Dip


  The angle of the rock strata in relation to the horizontal, a tectonic feature
• Factors affecting rock resistance

  • Whether rocks are clastic or crystalline
  • Amount of cracks, faults, fissures
  • Lithology of the rock
  • Dip of the rock strata
• Clastic rocks


  Sedimentary rocks made up of cemented sediment particles, therefore vulnerable to erosion
• Crystalline rocks


  Igneous and metamorphic rocks made up of interlocking crystals
• Erosion rates of different rock types

  • Igneous (Granite) - very slow less than a mm a year
  • Metamorphic (marble, slate) - slow 1 mm a year
  • Sedimentary (limestone) - very fast up to 10 cm a year
  • Boulder clay - even faster
• Permeable rock


  Porous rock that allows water to enter, can weaken rocks by removing the cement that binds sediment
• Vegetation is essential in stabilising coastal landforms from further change
• Ways vegetation stabilises coastal sediment

  • Roots of plants bind soil together to reduce erosion
  • Submerged plants provide a protective layer against erosion
  • Plants reduce wind speed at the surface to reduce wind erosion
• Halophytes


  Plants tolerant of salty conditions
• Xerophytes


  Plants tolerant of dry conditions
• Plant succession is a long-term change in a plant community in an area
• Conditions for salt marsh development in estuaries

  • Sheltered from strong waves, so sediment can be deposited
  • River transport a supply of sediment to the river mouth, which may be added to by sediment flowing into the estuary at high tide
• Wave types


  • Constructive - stronger swash than backwash, depositional, low height, low frequency, gentle beaches
  • Destructive - stronger backwash than swash, erosional, high height, high frequency, steeper beaches
• Waves break because the internal orbit of the wave reaches and touches the shore, friction from the sea bed distorts the wave
• Types of erosion


  • Abrasion (corrasion) - sediment thrown at cliff face
  • Hydraulic action - air trapped in cracks compressed by wave force
  • Attrition - sediment colliding to smaller fragments
  • Corrosion - chemical erosion
• Factors affecting erosion rates

  • Rock type and organisation
  • Wave type, fetch, frequency
  • Other weathering on the cliff face
• Erosional landforms


  • Wave cut notches and platforms
  • Cave-arch-stack-stump
• Sediment transportation processes

  • Traction - sediment rolls along
  • Saltation - sediment bounces along
  • Suspension - sediment carried in water
  • Solution - dissolved material carried in water
• The angle the wave attacks is the biggest determinant of sediment transportation