2.2 - Structure Influencing Landforms Flashcards
Key words:
- strata
- bedding planes
- joints
- folds
- faults
- dip
Bedding planes – horizontal cracks
Joints – vertical cracks
Folds – formed by pressure during tectonic activity, makes rocks buckle and crumple
Faults – cracks in the earths structure slip along fault planes
Dip – angle at which rock strata lie (horizontally; vertically; dipping towards sea or inland)
Concordant coasts
- where beds layers and rocks are folded into ridges that run parallel to the coast
- they usually have the same type of rock along its length - - dalmatian and haff morphology occurs on these coastlines.
Discordant coastline
- discordant: have bands of rock and layers that run perpendicular to the coastline
- the geology alternates between strata of soft and hard rock
- headlands and bays occur at these coastlines as erosion resistance is different between rocks
Dalmatian coasts
- off shore islands that run parallel to the coast
- concordant formed due to sea level rise
- when the valley flooded the tips of ridges remained above sea level
Half coasts
- these form where deposition produces unconsolidated geological structures parallel to the coastline
- concordant coastlines.
Concordant coastline case study - lulworth cove
- More resistant Portland Limestone runs parallel to the sea with less resistant Purbeck Limestone and Wealden Clay behind it
- The formation of coves has occurred where the water has broken through at weaker points in the Portland Limestone
Discordant coastline case study - swanage bay
- more resistant chalk forms the headland at Ballard point as well as old Harry’s rocks which are stacks
- wheldon beds and greensand are less resistant and erode more rapidly forming swanage bay
- preveril point and durlston head is a headland formed from the slower erosion of more resistant purbeck limestone
Wave refraction around headlands
- Wave refraction changes the amount of energy reaching the shore on a small local scale
- Wave energy concentrates at the headland and increases the rate of erosion
- waves bend towards the headland as the water depth becomes shallower more quickly
- this concentrates the energy at the headland and reduces the amount of energy reaching the bay
What is a cliff profile
the height and angle of a cliff as well as its features such as wave cut notches or changes in the slope angle
Cliff profile: horizontal dip
- uniform horizontal layers or bedding planes produce steep sided cliffs
- vertical/near vertical profile with notches reflected strata that are more easily eroded.
Cliff profile: seaward dip high angle
- rock slabs slide down the cliff along the bedding planes to form steep seaward dipping cliffs
- one layer of rock facing the sea vulnerable to rock slides
Cliff profile: seaward dip low angle
- joints opened up by weathering and pressure release slabs to from cliffs dipping seaward
- areas of overhanging rock very vulnerable to rock falls
Cliff profile: landward dip
- bedding planes dipping inland produce stable steep cliffs
- reduced rock falls at these cliffs as cliff is not overhanging
