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Geography > Coastal Landscapes and Change > Flashcards

Coastal Landscapes and Change Flashcards

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1
Q

Define Littoral Zone

A
  • dynamic area of change
  • area of dynamic equilibrium
  • different parts of the coast are undergoing constant short-term change
  • coasts vary in rate of change
  • variety creates different classifications of coastline
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2
Q

Parts of Littoral Zone

A
  • coast : land effected by sea e.g settlements/farmland
  • backshore : area above high tide level + only effected by extreme weather events e.g high tide
  • foreshore : zone between high/low tide marks + where wave processes take place
  • nearshore : just off coastline + beyond low tide + has shallow seawater
  • offshore : where waves start to break + water is deeper
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3
Q

Long term changes creates coastlines that are …

A
  • emerging/submerging depending on falling/rising sea-level
  • rocky/estuarine depending on weathering/erosion resistance
  • concordant/discordant depending on a geological strata/wave action relative position
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4
Q

Short term changes creates coastlines that are …

A
  • classified by tidal range
  • retreating / advancing depending on erosion/deposition
  • high/low energy depending on balance of erosion/deposition
  • land/marine based processes
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5
Q

Microtidal coast

A

<2m tide range

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6
Q

Mesotidal coast

A

2-4m tidal range

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7
Q

Macrotidal coast

A

> 4m tidal range

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8
Q

High energy coasts

A
  • large/powerful destructive waves
  • exposure to strong winds + long fetches + steeply shelving offshore zones
  • erosion > deposition BUT coastline geology = more resistant to erosion
  • rocky coasts + sandy coves + rocky landforms (cliffs/stacks/arches)
  • clear distinction between land and sea
  • cliffs w/ high erosion levels = steep + little vegetation
    ➕waves undercut cliff + wash away debris ∴ marine cliff profile
  • cliffs w/ high weathering = less steep as weathered material at base ∴ subaerial cliff profile
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9
Q

Low energy coasts

A
  • small gentle constructive waves
  • created by gentle winds + sheltered location + short fetches + gentle sloping offshore zones + may be protected by reef or offshore island
  • deposition > erosion
  • sandy beaches + salt marshes + estuaries + tidal mud flats + NO cliffs next to beach
  • Land w/ gentle relief + low elevation ∴ harder to identify parts of littoral zone
  • hit deposition levels due to stillness of water in estuaries + nearshore zone
  • sediment comes from land + sea
  • coastal accretion takes place (expansion or land into sea)
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10
Q

How waves are formed

A

1) wind blows over surface of water which creates waves
2) friction between wind + sea surface gives water circulation motion ad energy is transferred
3) ripples created which turn into larger waves over time
4) as waves approach shore , they break
5) friction w/ seabed slows bottom of waves , making motion fore elliptical
6) crest continues at same speed + rises up + collapses (wave breaking)

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11
Q

Conditions of waves

A
  • fetch
  • wind speed
  • ?
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12
Q

Destructive waves

A
  • high + steep
  • circular cross profile
  • short wave length ∴ high frequency = 10-14 per min
  • strong backwash ∴ removes material from beach
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13
Q

Constructive Waves

A
  • low frequency ∴ 6-8 per min
  • low + long = ellliptical cross profile
  • strong slash ∴ deposits material
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14
Q

Short term change to waves

A
  • storm event = more destructive waves
  • wind levels can change wave characteristics e.g high speeds = taller waves
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15
Q

Long term change to waves

A
  • seasonal changes e.g more destructive waves in winter + waves create berm in summer
  • climate change = more storm like conditions ∴ more destructive waves
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16
Q

Sediment cells

A
  • divide coasts into separate sections which are lengths of coastline that are self contained units
  • 11 cells in England+wales
  • sediments don’t move between cells
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17
Q

Sources of Sediment Cells

A
  • rivers carry eroded sediment from inland
  • cliff face erosion + weathering
  • accumulation of organism’s crushed shells
  • movement from offshore deposits(sandbanks) by waves/tides/currents
  • erosion of sand dunes (but only small)
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18
Q

Transfers of Sediment Cells

A
  • LSD
  • Offshore currents move sediment inland
  • wind
  • tidal currents move material in/out of coast daily
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19
Q

Sinks of Sediment Cells

A
  • flocculations of sediment in salt marshes
  • spit/bar formation
  • sand dunes form by wind action
  • offshore bars beneath waves
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20
Q

Define Sediment Budget

A

Amount of sediment entering + leaving system

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21
Q

Positive sediment budget

A

Sediment entering > sediment leaving = +ve sediment budget

∴growth

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22
Q

Negative sediment budget

A

Sediment leaving > sediment entering = -ve sediment budget

∴shrink

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23
Q

Dynamic equilibrium in sediment cells

A

Balance is maintained in a system w/ changing processes

E.g as waves erode beach , so does cliffs ∴ as material is taken away , material from cliffs is deposited so beach grows + system in balance

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24
Q

Positive feedback in coastal systems

A

As beach forms , friction causes waves to slow down + deposit. As beach grows bigger , even larger waves slowed down + more deposition continues

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25
Q

Coastal Landscapes of Discordant Coastlines

A

HEADLANDS and BAYS
- bands of alternating hard/soft rock perpendicular to shoreline
- once headland formed , it erodes quicker due to more exposure + wave refraction
- higher waves at headland as waves slow down , water behind crest builds up ∴ greater erosion power ∴ steeper cliff faces at headlands + arches/caves
- shape of bay dissipated wave energy = less height = less erosion
- over time difference between headlands and bays are less distinguishable

26
Q

Coastal Landscapes of Concordant Coastlines

A

COVES
- bands of rock parallel to shoreline
- waves break through hard rock then easily erodes the exposed soft rock fast till they reach hard rock again which is harder to erode

27
Q

Dalmatian Coastline

A
  • valley lies parallel to coast + increase in sea level can cause Dalmatian coastline
  • valleys formed by tectonic folding
  • folding creates anticlines (slope down) + synclines (slope up)
  • valleys flood as sea levels rise
28
Q

Haff Coastline

A
  • deposits of sand run parallel to to coastline on top of offshore bars
  • lagoons from between bars and shoreline
29
Q

Examples of Discrodant Coastlines

A

SWANAGE BAY:
- Isle of Purbeck , East Dorset
- formed from erosion of less resistant Wealden Clays
- faces east + sheltered from prevailing south westerly wind + highest energy waves.

30
Q

Examples of Concordant Coastlines

A

SOUTH DORSET COAST

31
Q

Strata

A

Layers of rock

32
Q

Deformation of Strata

A
  • Strata folding (bend/crumple) + dip (angle towards/away from sea)
  • as strata fold/dip , diff amounts of pressure experienced
33
Q

Joints

A

split rock into diff verticle blocks

34
Q

Bedding Planes

A

split rock into diff horizontal planes

35
Q

What does the profile of a cliff depend on

A
  • resistance of the rock
  • relative energy of a coastline
  • position of rock strata in relation to coastline
36
Q

Horizontal strata dip

A
  • waves erode softer rock creating notches on cliff face
  • if wave-cut notches = too large then cannot support rocks above ∴ rockfall
37
Q

Strata dipping away from sea

A
  • landward
  • no undercutting ∴ stable cliff
38
Q

strata dipping towards sea

A
  • seaward
  • gentle dipping = rocks breaking away in a wedge
  • steep dipping = rocks mass movement
39
Q

Coastal recession depending on bedrock lithology

A
  • igneous rock = highly resistant (1-5mm yearly) as hard crystalline structure = few joints
  • metamorphic rock = some resistance (1-10mm yearly) as crystalline structure aligned in one direction = more prone to folding + faulting
  • sedimentary rock = limited resistance (2-6cm yearly) as made of clastic rock which has many fractures + porous = permeable + vulnerable to erosion
40
Q

Clastic Rock

A

rock made form fragments of other rock

41
Q

Coastal recession depending on lithological structure

A
  • ROCK TYPE ORDER IN STRATA : if less resistant rock at bottom then more undercuttung = more cliff collapse = accelerating coastal recession OR multiple folds = more cracks + fractures = easier to exploit
  • ROCK PERMEABILITY : impermeable rocks = more surface runoff , permeable rock results in pore water pressure = weaker rock structure = enlargerning cracks/joints or permeable rocks results in more weight taken in by rainwater ∴ slumping / landslips / slip planes
  • ROCK REACTIVITY : some rocks contain compound that chemically react w/ seawater ∴ more vulnerable to erosion
42
Q

Mechanical Weathering

A
  • breaking rock material without changing chemical composition
  • freeze-thaw weathering
  • saline water causes salt weathering as water enters cracks at high tide , crystals from as rocks dry when tide leaves , expanding crack
  • clay rocks expand when wet
43
Q

Chemical weathering

A
  • breakdown of rock by changing its chemical composition
  • carbonation is where CO2 dissolves into rainwater to produce weak carbonic acid which reacts w/ calcium carbonate to slowly dissolve rock
  • Oxidation is when rocks containing iron react w/ oxygen in air and form iron oxide that makes rocks crumble easily
44
Q

Biological Weathering

A
  • weathering through actions of plants + animals
  • organisms may use cracks in rocks for burrowing/habitats which break apart rock
  • seeds may fall into cracks + plants grow ∴
    breaking rock open
45
Q

Mass Movement on Coasts

A
  • material moves downhill due to gravity
  • can occur when wave action undercuts cliffs and unsupporting overhand collapses
  • landslides + rockfall + rotational slumping
  • more likely for unconsolidated rocks as little friction between particles
  • heavy rain saturates rocks ∴ reducing friction
46
Q

Landslides

A
  • material moving in a straight line down a slope
  • quick
  • occur on steep slopes after heavy rainfall / storm conditions
  • rainfall reduces friction ∴ creating slip planes
  • landslide scar left behind (area of unvegetated rock)
47
Q

Rotational Slumping

A
  • materials sliding down slope at curved angles
  • material retains shape whilst sliding
  • takes long period of time
  • slip plane created when permeable soft rock lies ontop of impermeable hard rock
48
Q

Rockfall

A
  • broken blocks moving down slope
  • more common on steep cliffs w/ many joints + bedding planes
  • rock topple results in regolith (material at base of cliff)
49
Q

Weathering

A
  • weakens cliff face ∴ more vulnerbale to wave action
  • provides scree for waves to use as erosive tool (abrasion)
50
Q

Mass Movement

A
  • adds rock material to beaches
  • strengthens beaches by increasing size ∴ waves have more friction = less energy = less erosion
51
Q

Erosive Processes

A
  • hydraulic action = waves compress air into cliff face cracks = more pressure = rocks break off
  • abrasion = rock + sediment transported scrapes against cliffs = breaks sections of cliffs away + smoothens surface
  • attrition = rocks smash against each other into smaller/rounder pieces
  • corrosion = seawater dissolves soluble rocks (limestone/chalk)
52
Q

Formation of a Wave Cut Platform

A
  • wave erosion causes notch to form at high water mark
  • further erosion causes notch to get bigger
  • eventually forms cave
  • rock above cave = unstable ∴ collapses
  • new notch forms etc , leaving behind a wave cut platform
53
Q

Wave refraction

A

as wave approaches headland ,it enters shallow water + slows down due to fricion. waves far away are faster due to deep water ∴ refract

54
Q

Wave refraction landmarks

A
  • caves on opposite sides meet to form arch
  • sea spray erode top of arch + create blowhole
  • further erosion of blowhole makes arch collapse = stack
  • exposure of stack makes it smaller
  • undercut stack = stump
55
Q

Factors for Rate of Erosion

A
  • WAVE TYPE = destructive waves = more energy = strong backwash = more erosion
  • WAVE SIZE = larger waves = more energy = quicker erosion
  • LITHOLOGY = soluble rocks = softer + less resistant AND defined strata = more weaknesses
56
Q

Factors for Rate of Recession

A
  • TIDES : high tide = more area to erode AND frequency of spring/neap tides by climate change
  • WIND DIRECTION AND FETCH : long fetch = stronger waves AND winds from SW = stronger as fetch = 6500km long
  • WEATHER SYSTEMS + SEASONS + STORMS : low pressure = strong winds + more common in winter AND High pressure more common in summer + weak winds AND depression = low pressure AND climate change = more storms
57
Q

Human actions influencing coastal recession

A
  • building a dam interferes w/ sediment movement + less sediment for LSD to move ∴ quicker erosion further along coastline
  • coastal defences e.g groynes can retain sediment ∴ preventing LSD + more erosion further along
  • sand/shingle dredged from offshore bars = more erosion as sand removed from cell permanently
58
Q

Economic Loss of Coastal Recession

A
  • low lying coastlines = densely populated
  • coastal settlements have long term economic problems as lack of investment
  • land has different values e.g agricultural land is £23,000 per hectre wheres residential land in Dorset is £3.8m
  • heavy industry + essential services(power plants) not located near receding coasts as expensive to build
  • small businesses on receding coastline are abandones = less jobs + services
  • selling coastal property = hard + impossible to get insurance + property quickly loses value w/ a knock on effect of devaluing whole village
  • infrastructure on receding coasts = hard to reroute ∴ high economic burden on local govt
59
Q

Social loss of coastal Recession

A
  • isolation or disconnectedness as people + services leaving
  • amenity value lost as coasts recede + areas abandoned = visually unattractive
  • spiral of decline as people leave = service close down = loss of jobs = more people leave etc
  • rarely cliff collapse = fatalities
60
Q

Factors influencing sediment transport

A

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Geography (5 decks)

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