Coasts- Landforms & Landscapes Flashcards
Concordant coastlines
Rocks on these coastlines run parallel to the sea
Discordant coastlines
Rocks on these coastlines fun perpendicular to the sea
Wave cut platform formation
- waves breaking at the foot of a cliff produce a wave-cut notch (due to erosion by waves)
- as the cliff is undercut, the rock above collapses and so the cliff gradually retreats
- a sloping rocky platform (wave cut platform) is left behind, which is covered at high tide
How do wave cut platforms impact rates of erosion?
- as the platform grows the waves have further to travel in shallower water
- this means they tend to break earlier and dissipate their energy
- the rate of erosion of the headland is therefore reduced
- this limits further growth of the wave cut platform
What is a cliff profile?
The cliff profile refers to his steep the cliff face is at its meeting point with the sea
Impact of different bedding planes on cliff stability
- of bedding planes are horizontal then the cliff profile will be stable with a steep cliff face
- rock that has been lifted (due to tectonic movement) with its bedding planes tilted downwards away from the coast create very stable cliffs
- bedding planes that tilt upwards have a cliff profile similar to the angle of tilt- due to the frequency of mass movements that occur at the base of the cliff (from wave action)
How does a headland erode to form a stack?
- a headland is attacked by waves along lines of weakness
- this frequent erosion (eg. hydraulic action) forms a cave
- if the weakness runs through the headland, two caves may form back to back- eventually forming an arch
- wave attack continues at the base of the arch while sub-aerial weathering (eg.freeze thaw) attacks the roof
- eventually this roof collapses leaving a stack (an isolated column of rock)
What is a spit?
- a long narrow piece of land joined to the mainland which projects out to sea/across a river estuary
- a depositional landform made of sand and shingle
- form at drift-aligned beaches
Formation of a spit
- longshore drift moves material along the coastline in the direction of the prevailing wind
- as the coastline changes direction the finer material will continue to be transported out to sea
- this will build outwards and upwards and form a permanent feature
- material can’t extend to meet the mainland due to river currents in the estuary and increasing water depth
- wave refraction and secondary wind forces the material to move in a different direction-results in s curved end
Beach formation
- beaches form in a low energy environment where sediment must be present
- deposition must be the dominant feature where effects of waves are reduced
- beaches form when there is insufficient energy to move sediment further so it is deposited
- occur in the littoral zone (between low and high tide)
Beach profiles in the summer
- steeper in the summer
- waves are more constructive
- energy dissipates and deposits sediment over a wider area
Beach profile in winter
- destructive waves more common
- beaches eroded by high-energy waves
- sometimes backwash exerts a rip current dragging sediment back as the next wave arrives over the top
- so the beach profile flattens
Ridges and runnels
Ridges- sand accumulations at the lower edge of the beach (form longshore bars)
Runnels- channels through which backwash goes out to sea
What is sediment at the top of the beach like?
- larger pebbles
- backwash weaker than swash so large sediment can’t be dragged back into the sea
What is sediment at the bottom of the beach like?
- smaller pebbles
- more rounded due to constant actions of waves causing abrasion and attrition
- scree falling from cliff face can explain more angular sediment
Properties of swash aligned beaches
- form in low energy environments eg. bays
- waves arrive roughly parallel to the shore
- beach may consist of sand or shingle
- beach is self contained and length will not change as no longshore drift is taking place
Properties of drift aligned beaches
- form where the waves approach the coast at an angle
- longshore drift moves sediment along the beach- often accumulating in the form of a spit
- finer shingle particles likely to be carried further along the beach and become increasingly rounded
Compound spits
Spits with hooks on their land ward side
Simple spits
Bars of sand without barbs or hooks
Formation of tombolos
- formed when spits extend from the coast to an island
- may form in the ‘shadow’ of wave refraction caused by an offshore island
- can only form along low energy coastlines (constructive waves means deposition is dominant process)
- must be a supply of sediment to deposit
- must be a drift aligned coastline
Formation of bars
- when waves approach a gently sloping coast, friction between waves and the sea bed cause waves to break some distance from the coast
- overtime more material builds up parallel to the coast to form ridges called offshore bars
Lagoon
- form when a bar connects to headlands on either side of a bay and is large enough to be above sea level
- this bar is called a barrier beach
What are sand dunes?
Accumulations of sand blown into mounds by the wind (aeolian landforms)
Sand dune formation
- sand accumulates on the beach from longshore drift
- at low tide, the sand dries out allowing the prevailing winds to move the loose sand up the beach
- large inter tidal zone for sand to be dry (time between high and low tide)
- sand transported by saltation
- debris on beach traps sand (called strand line)
- grass grows which stabilises the dunes
How could you determine the age of a sand dune?
- size of the dune
- type of plants growing
- amount of vegetation
- luminescent dating (measure radiation to see when sand was last exposed to the Sun)
Embryo dune
- sand continuously moving
- high pH over 8
- high wind speed
- no more than 1m high
- 80% of sand exposed
- plant type: sea twitch and Lyme grass
Fore dune
- drought resistant plants colonise eg. Lyme grass and marram grass
- root systems bind sand together
- as they grow, more sand is trapped and dunes increase in height (up to 5m)
- 20% of sand exposed
Yellow dunes
- more diversity of plants
- humus layer builds
- pH slightly alkaline
- marram grass dominates other vegetation
- dunes 5-10m high
- 80% of sand vegetated
- rabbits and other mammals enrich soil
Grey dunes
- 100% vegetation
- 50-100m from sea
- sheltered from winds
- humus darkens allowing soil to form
- pH more acidic
- water content low
- 10m high and wider
Dune slacks
- found between mature dunes and where the water table reaches the surface
- plants adapted to damp and shelter
- peaty soil
Mature dunes
- 100m from shore
- if undisturbed can support shrubs, trees etc.
- humans may plant fast growing conifers
Pioneer species
The first plants that colonise an area, usually with special adaptations
Halophytes
Salt tolerant species eg. glasswort and cordgrass
-they can also tolerate the periodic soaking of the sea caused by tides
What are the required conditions for mudflat formation?
- sheltered areas where deposition occurs
- where salt and freshwater meet
- low energy coastline
Salt marsh succession
- as tidal currents slow, mud and small particles are deposited close to high tide line
- floccuation-particles of clay stick together to form a mass that can sink into the seabed
- pioneer plants colonise which trap further deposits of mud
- mud level rises above high tide and salt marsh developed- and a wider range of plants develop
- soil conditions improve and vegetation succession continues
- shrubs and trees colonise
- by this time the upper levels of the marsh are rarely covered by sea
How might sea level rise threaten salt marshes?
- land is of relatively low value so that have been declared areas of managed retreat
- the salt marsh will act as a buffer against erosion of the mainland
What are mudflats?
Created by the deposition of fine salts and clays in sheltered, low energy coastal environments (eg. estuaries)
What is a salt marsh?
An area of coastal grassland that is regularly flooded by sea water eg. Darwin, Australia
What human threats are there to salt marshes?
- industrial pollution eg. oil pollution- may harm marsh species
- dredging- removes sediment which may reduce mudflat accumulation and disrupt marsh ecosystem
- commercial and recreational shipping- erodes marshes
- grazing- causes trampling of species
