Coastal landscapes of EROSION and DEPOSITION Flashcards
Explain the formation of caves, arches, stacks & stumps (EROSION)
Occurs on pinnacle headlands:
Faults in headland are eroded by hydraulic action + abrasion to create small caves.
Overlying roc in cave may collapse, forming blowhole.
Marine erosion widens faults in base of headland, widening over time to create bigger cave.
Cave widens due to marine erosion and sub-aerial processes, eroding through to the other side of headland, creating arch
The arch continues to widen until it is unable to support itself, falling under its own weight through mass movement, leaving a stack
With marine erosion attacking base of stack, eventually stack will collapse into a stump
Wave-cut platform will be left afterwards
(Cliff profile) steep cliffs
Rock is strong and resistant to erosion. Sedimentary rocks that have vertical strata are also more resistant to erosion, creating steep cliffs. Most commonly found in high energy environments.
(Cliff profile) gentle cliffs
Found in areas w/ weaker rocks less resistant to erosion. Low energy waves and short fetch lead to formation of scree mound at base of cliff, reducing overall cliff angle. Large beach also reduce wave energy + prevent develop. of steep cliffs by reducing erosion rates. Commonly found in low energy environments
What is rate of retreat dependent on?
Dependent on relative importance of marine factors (fetch, beach, wave energy) and terrestrial factors (subaerial processes, geology, rock strength). Cliffs most likely to retreat = made of unconsolidated rock
How can negative feedback loops help to protect and restore the coast?
Eg. During storm, part of cliff may collapse so material produced protect base of cliff from marine erosion, reducing further cliff recession.
Explain the formation of wave-cut notch and platform (EROSION)
Occurs at steep cliffs
When waves erode cliff, erosion mostly concentrated around high-tide line. Main processes of hydraulic action + corrasion create wave cut notch
As notch becomes deeper (+ subaerial weathering weakens cliff from top) leaving behind platform of unaffected cliff base beneath wave-cut notch
Over time same processes repeat leading to wave-cut platform to form, normally exposed at high-tide
What negative feedback loop occurs as a result of wave-cut platforms?
Length of wave-cut platform limited as eventually waves no longer reach clidd, reducing erosion. Therefore act of erosion creating wave-cut platform has acted to directly decrease rate of erosion in future - negative feedback
Explain the formation of beaches (DEPOSITION)
Depositional landform - stretches from low tide to high tide line + is created when sediment deposited near coastline when waves lose energy.
Beach accretion occurs when beach being built up by constructive waves, usually in summer months. Beach excavation occurs in winter when destructive waves remove sediment from beach. Effectiveness of transportation = dependent on angle of prevailing wind + leads to formation of different types of beach.
Describe the different types of beach (DEPOSITION)
Swash-aligned beach: Wave crests approach perpendicular to coast so limited lsd. Sediment doesn’t travel far along beach. Wave refraction may reduce speed of high energy waves, leading to formation of shingle beach w/ larger sediment eg. Brighton
Drift-aligned: Waves approach at significant angle so lsd causes sediment to to travel far along coastline, which may lead to formation of spit. Larger sediment is found at start of beach + weathered sediment moves further down beach.
What are the different features w/in a beach? (DEPOSITION)
Berms: ridges marking where high tide line is at different times of year, as result may be several berms on beach characterised by small ridge or change in sediment type.
Cusps: small curved dips in beach where swash comes in, slightly lower than rest of beach, creating undulations in beach profile
Runnells: smaller ridges often found in smooth wet sand further towards sea, caused by the tides.
Describe the formation of spits (DEPOSITION)
Is long narrow strip of land formed when lsd causes beach to extend out to sea, usually due to change in direction of coastline. Sediment projection can create salt marsh due to sheltered, saline environment where water flow speed = lower, allowing deposition of finer sediments to occur.
Change in wind direction or wave direction can cause end of spit to curve (known as recurved end).
Explain the formation of bays and headlands (EROSION)
- from along a discordant coastline
- rock strata are of differing lithology exposed to wave action together along a coastline
- tougher, more resistant rocks (eg granite + limestone) form headlands w cliffs
- weaker rock (eg clays + shales) eroded to form sandy bays
- wave refraction is key process
What is accretion?
Accretion is the growth of a natural feature by enlargement. In this case of coasts, sand spits grow by accretion as do other land forms such as sand dunes.
Explain the formation of onshore bars and barrier beaches (DEPOSITION)
- bar is created where spit has developed right across bay bc no strong currents to disturb process
- this dams brackish water behind it, forming lagoon
- bars also develop as result of storms raking up pebbles + left in ridges offshore, shingle creates barrier beach
Explain the formation of salt marsh (DEPOSITION)
- sheltered river estuaries become areas of extensive accumulations of silt + mud (mudflats), aided by flocculation + gentle tides
- these inter-tidal areas = colonised by vegetation, + a halosere develops, creating salt marsh
- as vegetation becomes more dense, impact of tidal currents reduces; humus levels increase, allowing reeds + rushes to grow, later alder + willow
