coastal processes and landforms Flashcards
hydraulic action
-air trapped in cracks compressed by force of waves crashing against cliffs
-air trapped experiences greater force in next cycle of compression
-disloges blocks of rock from the cliff face
what rock type is vulnerable to hydraulic action
-heavily jointed/fissured sedimentary rocks
-in very hard igneous rocks, may be only erosive process operating
abraison
-sediment picked up is thrown against the cliff face
-chiselling away at surface
-wear down by removing small rock particles
influence of lithology on abraison
-subtly loose sediment has to be available like shingle or pebbles
-softer sedimentary more vulnerable than hard igneous rocks
influence of lithology on attrition
-softer rocks very rapidly reduced in size
attrition
-acts on already eroded sediment
-collisions between particles chip fragments of sediment
-sediment becomes smaller and rounded
what is a landscape (describe questions)
-two or more landforms
how does a wave cut platform form
-sea attacks base of cliff and undercut forming a wave notch
-notch becmes larger and weight of cliff causes it to collapse
-as cliff collapses, rubble washes away by waves causing abraison and forming a wave cut platform
steps of how a wave cut notch formed
-cracks at base of headland in inter tidal zone become exposed through hydraulic action
-cracks widened by weathering processes like salt crystallisation
-cracks develop into wave cut notches
how does a cave form
-abraison and hydraulic action deepen notch to form caves
-bc of wave refraction, destructive waves concentrate energy on sides of headland, deepens the cave
how do archs form
-wave refraction affects all 3 sides of headland and if 2 waves align, waves may cut through to form arch
how to stacks form
vertical joints exposed by tall breakers associated with destructive waves, over time arch becomes unstable and collapses under own weight to form a stack
whats swash aligned
-wind blowing directly onshore
whats drift aligned
-wind blowing in at an angle
what causes the waves to come back down at 90 degree
-friction from beach dissipates wave energy
what is wave approach angle determined by
-prevailing wind
whats traction
-when sediment rolls along pushed by waves and currents
whats saltation
when sediment bounces either due to force of water or wind
whats suspension
sediment carried in water column
whats solution
dissolved material carried in water in solution
what influences transportation
-currents
whats currents
-flows of seawater in a particular direction driven by winds or differences in water density, salinity or temperature
what are two depositional processes
-gravity settling
-flocculation
-occurs when energy of transporting water becomes too low
whats gravity settling
-large sediment deposited first followed by smaller sediment
whats flocculation
-small particles (like clay) clump together due to electrical or chemical attraction
-become large enough to sink
how does either swash or drift aligned longhsore drift affect bays
-wave refraction can cause either but typically more swash aligned
what is a spit
-sand or shingle beach ridge extending beyond a turn in the coastline
-at the turn longshore drift current spreads out and loses energy leading to deposition
what is the length of a spit determined by
-existence of secondary currents causing erosion (flow of river or wave action)
example of spit
-spurn head on the holderness coast
whats a bayhead beach and how is it formed
-swash aligned feature
-sediment moved into bay where beach is formed
-due to wave refraction erosion concentrated at headlands and bay becomes area of deposition
example of bayhead beach
-lulworth cove, dorset
whats a tombolo
-sand or shingle bar that attaches coastline to an offshore island
how do tombolos form
-due to wave refraction around an offshore island
-creates area of calm water and deposition
example of tombolo
-st ninians tombolo, shetland
whats a barrier beach/bar
-sand or shingle beach connecting two areas of land with shallow water lagoon behind
whats a cuspate foreland
-triangular shaped features extending out from a shoreline
-growth of two spits from opposing longshore drift directions
what do depositional landforms depend on
-sediment supply and direction of prevailing wind
what does a spit consist of
-largely unconsolidated material
why does river discharge prevent a spit continuing
-disrupts the sediment flow
-causing sediment starvation (which also may be due to human interaction)
what two things can happen if wave energy increases to a spit
-destructive waves either:
-cause a loss of sediment, overtopping removes vegetation, destabalising so reduced size of spit
-or cld bring sediment so build up a spit
in order for a spit to form, what must be balanced
the dynamic equillibrium
what do depositional landforms depend on
sediment supply and direction of prevailing wind
