booklet 3- coastal landforms Flashcards
(39 cards)
1
Q
what are the erosional landforms?
A
wave cut platform
blowhole
cave, arch, stack , stump
headlands and bays
2
Q
wave cut platform how are they developed?
A
- high energy coastlines , hydraulic action and abrasion can cause the formation
- powerful destructive waves attack base of cliff at high tide
- hydraulic action and abrasion creates wave cut notch which over time increases in size (called undercutting)
- eventually overhand created by undercutting collapse due to weathering and gravity
-cliff retreats = leaves wave cut platform that’s exposed at low tide
3
Q
another step by step development of wave cut platforms
A
- hydraulic action and abrasion= wave cut notch
- wave cut notch increases in size= overhang
- unsupported overhang collapses due to gravity and weathering at top of the cliff
- backwash transports material from cliffs base = leaves wave cut platform
4
Q
is wave cut platform positive or negative feedback?
A
negative because length of wave cut platform is limited as eventually waves can no longer reach cliff = reduces erosion
5
Q
what is a blowhole?
A
a cavity formed when a joint between a sea cave (formed by erosion) and land surface above cave becomes enlarged. Sea cave and land surface becomes conjoined when roof of cave collapses
6
Q
is a blowhole a positive or negative feedback system?
A
positive
7
Q
step by step process on how blowholes are formed?
A
- initial weakness joints etc
- wave action erodes weaknesses= widens them into caves
- weathering = pothole like depression of cliff surface
- wave erodes further into cliff. Pothole deepens and they eventually meet
- blowhole= channel for waves to travel into cave
- powerful wave action = pressure of water inside cave can force water out through the top of the blowhole
8
Q
example of a blowhole?
A
Cayman blowhole , ‘ironshore’
—> limestone foundation around island= eroded = holes= tide comes up through hole, overtime roof collapses and geo is formed
9
Q
what kind of coastline are headlands and bays formed on?
A
- discordant coastlines alternating hard and soft rock
10
Q
headlands and bays over time impacts
A
- more freeze thaw in winter
- more rainfall= mass movement due to more lubricant surfaces
- sea levels rising and climate change
- UK November - May= higher rates of erosion
- more biological weathering in summer
11
Q
headlands and bays formation
A
- headlands = harder rock, cracks and joints widen from hydraulic action
- wave energy focused on headlands as they stick out= speeds up breakdown
- bays= softer rock and erode faster at start, then waves lose energy in bays as more sheltered = deposition of sediment and beaches form = further protection from erosion
- eventually headland eroded away = more erosion in bays again —> dynamic equilibrium if conditions stayed constant
12
Q
what contributes to the formation of cave arch stacks and stumps
A
- at a headland where rock is hard, erosions slow and can create varied landforms
- wave refraction concentrates wave energy onto headland and can contribute to formation of caves, arches, stacks, stumps
—> joints in headlands = susceptible to erosion by hydraulic action —> joints widen = form cave= enlarged by hydraulic action and abrasion = cuts through headland and forms an arch
—> roof of cave collapses due to gravity and lack of support
—> leaves a stack which overtime is eroded by weathering , abrasion and hydraulic action = forms a stump
13
Q
step by step formation of cave arch stacks stumps
A
- large crack opened by hydraulic action
- crack grows into cave from abrasion and hydraulic action
- cave breaks through headland and forms an arch
- arch is eroded and collapses
- leaves a tall rock stack
- stack is eroded forming a stump
14
Q
factors affecting landform development
A
- resistant rock e.g. basalt, granite= withstands waves, vertical cliffs e.g. Cornwall , Atlantic coast
vs
less resistant rock e.g. clay, sandstone = erode easier , may create gently sloping cliffs - structure
—> discordant = alternate bands more and less resistant geology = bays, headlands, arch, cave, stacks, stump , beaches form
—> concordant coastline = geology runs parallel to the coastline = steep cliffs if hard geology , crumbly low cliffs if softer geology , narrow beaches - human coastal management
- more erosion elsewhere
- wind strength, fetch
- vegetation (bind soil= less erosion)
- climate
- tectonic activity
- mass movement
- rock structure
15
Q
what are the erosional landforms?
A
beaches
spit
tombolos
bars
sand dunes
estuarine mudflats and salt marshes
16
Q
where do depositional landforms occur?
A
at low energy coastlines when waves don’t have enough energy to carry a large sediment load
17
Q
what is a beach?
A
where the land meets the sea
a store in coastal systems
form when constructive waves deposit material on shore
18
Q
shingle vs sand beaches
A
shingle e.g. Chesil Beach, UK
- steep and narrow as made of large particles which pile up at steep angles
sand e.g. Honko beach, Finland
- wide and flat as they’re made from smaller particles
—> when wet sand becomes compressed and allows little percolation = most swash returns as backwash = forms ridges and tunnels
19
Q
what is accretion?
A
process where sediment is added to a landform building it up over time
20
Q
what is swash aligned vs drift aligned beaches?
A
- see diagram
swash aligned - low energy environments
- generally waves more parallel to shore
- experience minimal longshore drift
drift aligned
- form where longshore drift moves sediment along the beach as waves approach at an angle
- often turns into a spit where coastline changes direction
21
Q
beach features?
A
- Berms- ridges of sand/sediment found at back of beach above high tide line —> look like ‘beach steps’ = flat platforms or steps making former high tide lines
- Ridges= elevated areas of sand running parallel to shoreline, often form with runnels
- Runnels- shallow trough/channels between beach ridges, help drain water off beach
- Cusps- semi-circular depressions in beach face , formed when waves break at an angle = swash and beach wash material mixes
22
Q
beach profile?
A
- constructive waves carry material lots of sizes up beach due to strong swash but water percolating into beach, weaker backwash so only small sediment is carried back= larger sediment at top of beach, smaller at bottom —> smaller at bottom = more rounded as more wave action on them
- seasonal changes —> sediment put offshore by destructive waves in winter and returned by constructive waves in summer
- steeper in summer (more constructive waves) vs more destructive in winter
23
Q
how do spits form?
A
- see diagram on mindmap
-created due to longshore drift (+ prevailing winds) - sediment transported by waves along coastline
- coastline changes direction= waves no longer have energy to carry sediment and its deposited
- build up of deposited material out to sea often into estuary= spit
- spits often have curved end/ hook due to secondary prevailing wind
24
Q
what type of coastline do spits form on?
A
discordant
and often on drift - aligned coastlines
25
simple vs complex spit
simple has only one recurved end vs complex has multiple curved ends
26
example of a spit ?
Hurst Castle Spit, Hampshire, England —> South Coast england
- has lots of groynes and boulders to protect it
bay meant it was almost lots BUT stabilisation scheme rebuilt it with dredged shingle
—> has lots of plants, a hook and has been impacted by storms
27
what is a tombolo?
beach between small island and mainland (often due to a spit continuing to develop)
e.g. Chesil beach south coast, links Portland to mainland
—> can be covered at high tide
28
what is a barrier beach (a bar)?
where a beach / spit extends across a bay to join two headlands
e.g. Start Bay, Devon
- they can trap water behind them = forms a lagoon
- lots of sediment in bar = deposited by meltwater from rising sea levels after glacial period
29
are barrier beaches and offshore bars the same thing?
NO
- beach is separated from mainland = barrier beach often parallel to coastline and not submerged
- offshore bars= submerged ridges of sand/sediment created by waves offshore from coast —> they can absorb energy
KEY DIFFERENCES
- offshore bars = underwater, mobile, offshore
- barrier beaches (bars)- above sea level, parallel to mainland, larger, more continuous, separated by lagoons
30
what are sand dunes?
accumulations of sand shaped into mounds
- dynamic equilibrium
31
sand dunes inputs
- plentiful supply wand
- strong inshore winds / prevailing winds
- large tidal range
- obstacle to trap the sand
- vegetation growth= encourages further dune growth
- sand = moved inland by saltation
- during day wind on coastal range = from sea due to differential heating of land sea and differences in localised atmospheric pressure
- large tidal range = large amounts of sand exposed at low tide = dune formation
- vegetation succession and development of sand dune psammosere ecosystem
32
sand dunes development
- sand trapped by obstacle (sea week, rock, drift wood, litter etc)
- embryo dunes develop —> suitable for colonisation by grasses = grow up and accumulate sand , stabilise surface —> long roots of marram grass= bind sand together
—> plants add organic matter to dunes = adds water retention
- embryo dunes raise and become fixed and more vegetation accumulates
- dune slacks develop (depression within dunes where water table is on/near surface and conditions = damp
- behind yellow/grey dunes sand supply= cut off smaller dune features
- blowouts can also be found where wind has funnelled through areas and removes the sand —> human activity can catalyse this
33
sand dunes vegetation succession
- first colonising plants= pioneer species —> have special adaptations to survive e.g. sea rocket and couch grass can cope with dry salty conditions —> when die they add organic matter to developing soil
- pioneer plants bind sand = forms fore dunes. Marram grass found here —> it has long roots to seek water and binds sand
- overtime more species colonise until stable —> final community adapted and is called climatic climax community area
34
order of sand dune succession
embryo dunes —> fore dunes —> yellow dunes —> grey dunes —> dune slack —> woodland (mature dunes)
35
order of plant succession on a sand dune
fore dunes= sea rocket, couch grass —> yellow dunes = marram grass —> grey dunes= low shrubs (brambles) —> dune slack= aquatic plants —> woodland= oak trees, pines
36
what is an example of sand dunes?
camber sands, UK
37
estuarine mudflats and salt marshes some points.
- river estuaries = sediment stores
—> where river sediment is deposited (as velocity slows as river meets sea)
—> most sediment that accumulates = mud due to low velocities= mud flats form and develop into salt-marshes (areas of flat, silty sediment)
38
environments salt marshes develop in?
- sheltered areas when deposition occurs
- where salt and freshwater meet (e.g. estuaries )
- where they are no strong tides / currents to prevent sediment deposition and accumulation
- salt marshes = covered at high tide and exposed at low
39
estuarine mud flats and salt marshes development?
- mud deposited close to high tide line , dropping out of water by process, flocculation (tiny particles of clay (mud) sticking together and combine = mass enables them to sink)
- pioneer plants (eelgrass, cordgrass) colonise in transition zone between high and low tide -> these tolerate inundation by salty water and trap further deposits of mud as they help slow tidal flow
- mud level rises above high tide and lower salt marsh develops with more range of plants that don’t need to be as adapted to salty conditions
- soil conditions improve and vegetation succession continues = forms meadow
- shrubs and tress eventually colonise area as succession reaches climatic climax
- as sediment accumulates surface becomes drier = meadow grass etc accumulates
- creeks = divide up the salt marsh
