1. Coastal Landscapes Flashcards
The littoral zone
- a series of sub-zones to represent the features of the wider coastline from sea to land
- 4 key sub-zones : offshore nearshore foreshore and backshore
- reaches dynamic equilibrium when there is a balance between outputs and inputs
Littoral zone inputs / outputs
Sediment is the key input and output of the system and us determined by
Inputs - the action of waves, currents and wind
Outputs - washed out into sea by erosion
High energy coasts
Destructive waves ling fetches high rates of erosion caves, arches stacks and stumps Cliffs Wave cut platforms
Low energy coasts
Constructive waves Shorter ferches Higher rates of deposition Spits and bars Beaches Sand dunes Salt marshes
Concordant vs Discordant
Shape of coastline continually changing due to the surrounding geology which contributes to its morphology
Concordant - alternate bands of hard and soft parallel to coastline
Discordant- alternating bands of hard and soft rock at 90’ to coastline
Example of discordant
Dorset consists of Portland limestone and greensands
Greensands is less resistant to erosional processes
This has resulted in creation of bay and headlands
Dalmatian coasts
- Concordant/pacific coasts lead to the formation of Dalmatian coasts
- Made up of offshore islands and coastal inlets running parallel to coastline
- e.g. Lulworth cove on SW Dorset coastline where more-resistant limestone rock acts as barrier to protect less-resistant rock
Atlantic Coasts
Headlands and bays form on discordant/Atlantic coasts
As faster eroding-less resistant rock retreats (e.g clay at swanage bay) it leaves behind the more-resistant rock as headlands
Bays and headlands
- on discordant coastlines, the retreating rock and exposed resistant rocks cause a change in the shape of the coastline leading to wave refraction
- this change in the way in which waves approach the coastline can cause increase in rate of erosion on the headlands
- leads to headland features e.g. caves, arches, stacks and stumps
Joints and faults
- geological structure of the rock is caused by deformation and stress places on them from tectonic plates
- rocks with the presence of more joints and faults, like sedimentary rocks, are more susceptible to the process of erosion and weathering
- this is because these processes exert forces on the weakness found in layers of the rocks
Dip
- the angle the rock layer forms with the horizontal bedding plane is refered to as the dip
- bedding planes that dip towards sea create gentler cliff profile but vulnerable to mass movement processes like rockfalls
- bedding planes that dip towards land tend to create steeper cliff profile which are more vulnerable to processes like hydraulic action and abrasion
Bedrock lithology
- the physical properties of different rocks
- existence of sedimentary, igneous and metamorphic rocks affect the rate of recession along a coastline
Igneous rocks
- form from crystallisation of magma
- more resistant to erosion and weathering
- contain crystals which increase the strength of the rocks and reduce the number of lines of weakness which would be exploited by physical processes
- average rate of erosion 0.1-0.5 cm per year
- basalt and grantie
Sedimentary rocks
- Form from the build u0, compacting and hardening of sediments into layers over time by lithification
- when formed in shorter geological time scale they tend to be more susceptible to erosion and weathering than those formed over longer
- average rate of erosion 2-6 cm per year
- limestone and chalk
Metamorphic rock
- Formed from change in structure of sedimentary / indigenous rocks caused by variations in heat and pressure
- resistant to erosion
- marble is a metamorphic rock that has been formed from the changing structure of limestone caused bu the re-crystallisation on calcite
