Geological structure and landscape

• Geological structure

  refers to the arrangement of rocks in 3 ways:

  • strata - different layers of rocks within an area and how they relate to each other
  • deformation - the degree to which rock units have been deformed (tilted or folded) by tectonic activity
  • faulting - the presence of major fractures that have moved rocks from their original positions
• Concordant coast

  • aka pacific coasts
  • generated when rock strata runs parallel to the coast
• Discordant coasts

  • aka atlantic coasts
  • forms when rock strata intersects the coast at an angle
• Headlands and bays

  • happens on discordant coast
  • less resistant rock is eroded to form bays and more resistant geology remains as headlands
  • headlands tend to be eroded more than bays so eventually the difference is reduced and the coastline 'smooths' because of wave crests
• Wave crests

  • are the highest point of waves
  • in deep water wave crests are parallel
  • as waves approach the shore and shallower water, they slow and wave height increases
  • in bays, wave crests curve to fill the bay and wave height decreases
  • the straight wave crests refract, become curved then spread out in bays and concentrate on headlands
  • the overall effect of wave refraction is to concentrate powerful waves at headlands (greater erosion) and create lower, diverging wave crests in bays (reduced erosion)
• Cliff profiles are influenced mainly by the resistance of the rock and the dip of rock strata
• Dip

  • the angle of the rock strata in relation to the horizontal
  • is a tectonic feature
  • sedimentary rocks are formed in horizontal layers but can be tilted by tectonic forces
• Dip types

  • horizontal - vertical profile with notches where strata is more easily eroded
  • seaward, high angle - sloping cliff with one rock layer facing the sea, vulnerable to rock slides
  • seaward, low angle - profile could tilt further than 90 degrees so areas overhang leaving it very vulnerable
  • landward dip - steep profile of less than 90 degrees so is a very stable cliff with reduced rock falls
• geological features of cliff profiles

  • faults - major weaknesses within layers caused by a fault line that leaves rock heavily fractured and broken, leaving it vulnerable to marine erosion
  • joints - occurs in most rock, often in regular patterns that divides rock into blocks of regular shape
  • fissures - smaller cracks often only a few centimetres or millimetres but are still weaknesses for erosion to exploit
• The coast of Dalmatia, in the Adriatic Sea is another example of a concordant coastline. It was drowned by sea level rise during the Holocene. The geology of Dalmatia is limestone. It has been folded by tectonic activity into a series of anticlines and synclines that trend parallel to the modern coastline. This underlying structure of upstanding anticlines (above sea) and lower syncline basins (which would have been eroded by rivers in the past) has been drowned by rising sea levels to create a concordant coastline of long, narrow islands arranged in lines offshore