Geological Structure and Landscape [8.2 + 8.3]

• 3 Key Elements of Geological Structure:

  • Deformation: Degree to which rock units have been deformed (tilted/folded) by tectonic activity
  • Strata: layers of rock in an area and how they relate to each other
  • Faulting: when major fractures that move rocks from their original position are present
• Concordant Coast: rock strata run parallel to coastline
• Discordant coast: different rock strata intersect coast at angle so geology varies along coastline
• Faults: major rock fractures produced by tectonic forces and involves displacement of rocks on either side of fault line
• Unconsolidated sediment: uncompacted and uncemented material e.g sand ; loose and easily eroded
• Pore water pressure: pressure water experiences at a particular point below water table due to weight of water above
• Rate of recession: how fast a coast moves inland
• Geological structure influences the development of coastal landscapes at a variety of scales
• Coastal morphology: the shape and form of coastal landscapes and their features
• Lithology: The physical characteristics of particular rocks
• The morphology of a coastline will be determined by:

  1. The lithology or physical characteristics of the rock
  2. The relief and slope (cliff profiles)
  3. The rock type (sedimentary, igneous or metamorphic) and permeability (impermeable or permeable)
  4. How resistant to erosion the rocks is
• Rock type at the coastline is one of many dynamic factors that influences rates of erosion and weathering (processes) and the landforms that they create (outputs)
• Type of rock will influence its permeability which in turn will affect the rate at which it is eroded as well as the features that will be formed at the coastline
• Igneous rocks (granite, diorite, basalt) are crystalline, resistant and impermeable
• Sedimentary rocks (limestone, chalk, sandstone, shale) are formed in strata (layers). Jointed sedimentary rocks (sandstone and limestone) are permeable. Other sedimentary rocks (chalk) have air spaces between their particles making them porous. Shale is fine and compacted, making it impermeable.
• Metamorphic rocks (marble, schist, slate) are very hard and resistant; impermeable
• Geology and lithology will also affect the rates of erosion and the speed at which the coastline recedes. Weathering and mass movement processes will also affect the rate of erosion.
• Other factors that affect the erosion rate include:

  • High energy waves (driven by strong prevailing winds/long fetch)
  • Absence of a beach
  • Rising sea levels
  • Coastal management/sea defences elsewhere along the coast
• Geological structure produces two dominant types of coast:

  • Concordant are generated when rock strata run parallel to the coastline
  • Discordant form when different rock strata intersect the coast at an angle so geology varies along the coastline
• Discordant

  • Rock layers are perpendicular to the coast
  • Headlands and bays
  • E.G SW Ireland - Bantry Bay and Dingle Bay
• Concordant

  • Rock layers are parallel to the coastline
  • Unusual
  • Coves
  • Can be featureless
  • E.G Lulworth Cove, Dorset
• Part of Dorset coastline in UK running north from the Portland limestone of Durlston Head is a clear example of a discordant coastline
• Portland limestone is resistant to erosion; then to the north there is Swanage Bay where the rock type is a softer greensand
• North of Swanage, the chalk outcrop creates the headland which includes Old Harry Rocks
• A concordant coastline occurs where bands of differing rock types run parallel to the coast
• The outer hard provides a protective barrier to erosion of the softer rocks further inland
• Sometimes the outer hard rock is punctured allowing the sea to erode the softer rocks behind
• This creates a cove which is a circular area of water with a relatively narrow entrance way from the sea
• Wave refraction:

  • Bending of a wave as it spreads over different depths
  • Happens due to shallow water depths actually slowing down the wave whilst the part of the swell moving over deep waters continues at the same speed
• Dalmatian coast is namd from Dalmatia on Adriatic sea
• Dalmatian coast features long offshore islands and coastal inlets parallel to the coastline
• Adriatic sea itself is a concordant landform and consists of a body of water between parallel ranges
• Formed where the geology creates valleys parallel to the coast so that when sea level rises, a series of elongated islands remain offshore
• Haff Coastlines

  • Haff coasts: Long spits of sand and lagoons aligned parallel to the coast
  • Sand ridges form bars across some bays and river mouths, with trapped water forming a lagoon behind (called haffs)
  • E.G: these are named after the Haffs (lagoons) of the Southern shore of the Baltic Sea, which are enclosed by sand dunes or spits
• Rate of erosion igneous rock - very slow < 1 mm/yr
• Sedimentary rock rate of erosion - moderate to fast - 10 cm to several m per year
• Metamorphic rock rate of erosion - slow - 1 mm to 10 cm per year
• Halophytes: tolerate salt water
• Xerophytes: tolerate very dry conditions
• Vegetation stabilizing sediment:

  • Roots bind sediment particles together hence making them harder to erode
  • Plants protect sediment from wind erosion (aeolian process) by decreasing surface wind speed and reducing friction
  • Plants growing in sediment when submerged provide protective layer against moving water hence preventing erosion as it limits direct exposure