Coastal Landforms 🏝️ Flashcards
erosional landforms (5)
- cliffs
- wave cut notch
- headlands
- bays
- CraCASS
depositional landforms
- beaches
- spits
- offshore bars
- tombolos
- barrier island
- sand dunes
- mudflats
- salt marshes
headlands and bays
- bands of alternating hard and soft rock run at right angle to shore
- soft rocks eroded quicker to make bays
- hard rock eroded slower to make headlands
concordant coastline
alternating bands of hard and soft rock that run PARALLEL to coastline
discordant coastline
alternating bands of hard and soft rock that run at RIGHT ANGLES to coastline
wave cut platform
- destructive waves break a foot of cliff, energy concentrated
- erosion (hydraulic action and corrosion) creates wave cut notch
- rock above the cave becomes unstable (lack of support) and collapses
- leaves behind a flat surface when the cliff is eroded
example of negative feedback - cliff retreats to where waves can’t reach as easy
important factors:
- destructive waves
- winds (fetch, strength, duration)
= erosion
CraCASS - cliff profile features
form on headland, where wave energy is focused - due to wave refraction
- cracks in cliffs are eroded into caves (hydraulic action)
- caves on opposite sides of a headland may join to form an arch
- arch collapses (roof weathered by subaerial processes) and forms a stack
- stack eroded (and weathered) into a stump
important factor:
- high energy waves
- wind (fetch, duration, strength)
= erosion
- geology (alternating rocks)
beaches
accumulations of sediment that form when sediment is deposited on the shore - by constructive waves
- formed of sand or shingle
- material from offshore sand bars, longshore drift, wind, mass movement
can be drift or swash aligned
store of sediment
- berms = ridges of sand at high tide marks
- ripples due to action of tides moving across the sand
- ridges form where backwash deposits sediment (broken by runnels) at low tide mark
important factors:
- deposition
- wind - low energy to create constructive waves
- swash aligned (build up)
formation of a spit
spits are long, narrow ridges of deposited sediment which are joined to the mainland at one end
form where the coastline changes direction - eg across river mouth
the area behind a spit is sheltered, often becomes a salt marsh or mudflat
longshore drift continues to deposit sediment across river mouth, leaving a bank of sand and shingle sticking into sea
- simple spit - a straight spit that goes roughly parallel to coast
- compound spit - occasional changes to dominant wind and wave direction causes a recurved end
overtime, multiple recurved end may be abandoned a direction changes to normal
important factors:
- sediment supply
- longshore drift
- deposition (low energy env)
formation of a barrier beach (bar)
formed when a spit joins 2 headlands together
can happen across a river mouth or bay
lagoon forms behind the bar
important factors:
- longshore drift (prevailing wind)
- deposition (low energy env)
what is a tombolo
a bar that connects the shore to an island
important factors:
- longshore drift (prevailing wind)
- sediment
- depositon (low energy)
formation of a barrier island
long, narrow islands of sand or gravel that run parallel to shore, detached
form where there is a good supply of sediment, gentle slope offshore, powerful waves
- formed after last ice age when there was rapid sea level rise
- rising waters flooded land behind, transported sand offshore
- deposited in shallower water creating and island
- lagoon or marsh forms behind, sheltered from waves
- may also be bar detaches from shore by erosion
important factors:
- sediment
- deposition (low energy)
sand dunes
formed when sand deposited by longshore drift is moved up the beach by WIND
- psammosere - succession on sand
- sand gets trapped in debris, eg driftwood
- colonised by pioneer species eg couch grass
- vegetation stabilises the land and encourages more sand to accumulate - embryo dunes
- decaying plants add organic material, aids water retention
- more plants able to grow, lots of marram grass
- eventually become out of reach of the tide - yellow dunes (20% sand)
- humus increases, more plants grow - grey dunes
- overtime, oldest dunes migrate inland, have woodland, final stage of succession - mature dunes
as they get further from sea:
- pH decreases
- humus increases
- water retention increases
important factors:
- wind
- sediment
- vegetation colonisation
formation of a mudflat (estuarine landforms)
form in sheltered, low energy environments
eg behind spits, river estuaries
slow flowing water from river meets saline water - flocculation
caused sediment to be deposited
or sheltered areas behind spits cause deposition
silt and mud are deposited
important factors:
- deposition (low energy)
formation of a salt marsh (estuarine landforms)
sheltered low energy environments
silt and mud deposited to make mudflat
- mudflat colonised by pioneer species that can survive salt levels and being submerged by tide often
eg eelgrass
-trap more mud and silt - deposition continues and plants grow and die - gradually builds marsh upwards
- eventually exposed for longer between tides
- more complex plants can then grow - which are less tolerant to salt
eg sea lavender - more deposition and larger plants - raises marsh more
- eventually they are higher than highest spring tides
- most complex species can grow
eg trees
important factors:
- colonisation by vegetation
- deposition (low energy)
