A Level CIE Geography: Coastal Environments

pg.243

coast

narrow zone where land and sea meet and directly interact [varied and rapidly changing of al landscapes]

coasts are the most…

rapidly changing of all landscapes

four factors affecting the coastline

marine, human, atmospheric, terrestrial

two atmospheric factors affecting the coastline

• climate - wind, temperature, rainfall etc.

• climate change e.g. global warming, ice ages

three terrestrial factors affecting the coastline

• tectonic movements

• geology - rock type and rock structure

• ecosystems - sand dunes, salt marshes, mangroves

five marine factors affecting the coastline

• wave action

• longshore drift

• currents

• tides

• salinity

nine human factors affecting the coastline

• coastal settlements

• recreation and tourism

• port construction

• farming

• land reclamation

• sand and gravel extraction

• pollution - land-based and marine

• conservation

• coastal management

what are the main agents of change in coastal environments

waves

what are waves caused by

frictional drag of the wind as it blows across open water

wave direction is a reflection of

wind direction

what three factors do the size of wave and wave energy depend on

• wind speed

• length of time that wind blows in constant direction

• length of the fetch

fetch:

distance of sea over which wind can blow

which coastlines have larger fetches and which have smaller

coastlines that face large ocean e.g. west ireland = larger. coastlines around enclosed sea e.g. south france = smaller

the greater each of the three wave size factors is…

the bigger the waves

where are the biggest waves and why

southern ocean at forty and sixty s where westerly winds blow continuously, avg five m in height w/ some twice the height

where are the smallest waves and why

around equator where wind speeds are low particularly where winds fetch is limited by islands e.g. indonesia and enclosed seas e.g. mediterranean and caribbean bc reduced fetch available for wave gen.

once created, waves move in what direction

same of the wind that created them

why is it only the wave form that moves

water particles simply rotate in circular/elliptical movement as the wave passes through, it is the energy of the wave that moves towards the shore, not the water.

when does wave energy translate into the movement of water towards the shore

when a wave breaks

wave crest:

as the water in a wave rises, it forms the wave crest. top of the wave

wave trough:

as the water in a wave falls, it forms wave trough - low point between two wave crests

wave height:

difference in height between wave crest and wave trough

wave length:

distance between two wave crests. not usually evenly spaced

wave period:

time taken for a wave to travel through one wave length

wave velocity:

speed of movement of the wave crest calculated by avg wl/avg wave period

wave frequency:

no. waves that break on beach in given period of time

wave steepness:

calculated by wave height/wl. ratio cant exceed [1:7/0.14] bc at that point wave breaks

wave energy:

in deep water energy of wave is proportional to the wave length multiplied by the wave height squared meaning a small increase in wave height = large increase in wave energy. wave energy directly related to wave height and energy released when breaks.

plunge line:

point which wave breaks

swash:

body of foaming water that rushes up beach when a wave breaks. obtains energy from energy released by breaking wave.

backwash:

water which returns down beach after wave has broken

how are waves classified

often depending on how they break when they approach the shore and move into shallow water

nature of breaking wave is related to…

its energy

as waves moves into shallow water what happens to the movement of the water and why [depth of water less than half the wavelength]…

the movement of the water within the wave is slowed because of friction with the sea bed which reduces wave velocity reducing wavelength and increasing wave height.

as waves move into shallow water what happens to the movement of water particles and base of wave

the movement of water particles becomes elliptical rather than circular and the base of the wave slows down compared to crest.

what happens as wave steepens when moving into shallow water

breaks and rushes up the beach as swash dissipating wave energy as it moves against the friction of the beach.

what happens when waves break directly against cliff or sea

wave energy is directed against the vertical surface and erosion can be extremely effective

what kind of beach protects the coastline behind the beach against erosion and why

wide, gently sloping bc it can absorb most of the energy

high energy wave example

storm wave [type of destructive wave]

how are storm waves formed

strong winds blowing from the ocean directly onto the coastline

how are plunging breakers formed

when storm waves break on a steeply sloping beach

what happens when storm waves break

become vertical and plunge down onto beach

destructive wave features seven

• remove sediment from beach

• steep

• high

• short wl

• high wave frequency [over ten per min]

• often storm waves

• driven onto beach by strong onshore wind

what happens when destructive waves break

they crash down onto beach and much of water in breaking wave returns to sea rather than rushing up the beach so as a result they have weak swash and strog backwash

what happens to sediment in destructive waves

removed from beach by strong backwash and often builds up as longshore bars near low tide mark1

low energy waves example

swell waves

how are swell waves formed

when wind that made waves dies down over ocean, wave1s will continue to move in same direction until coastline reached without stimulus of wind so wave height decreases and wave length increases.

what is the effect of swell waves on a beach

they arent very steep so as they approach the beach, the crest of the wave stays smooth and the wave slides or surges up beach even if beach is steep resulting in surging breakers

constructive waves example

surging breakers

constructive wave features five

• low

• gentle

• add sediment to beach

• long wave length

• low wave frequency [less than eight per min]

what happens when constructive waves break

spill up on the beach producing a strong swash but the backwash is weak especially on gently sloping beaches.

breaking waves diagram

breaking waves

what do constructive waves do to sediment and how are berns formed

push sand and sediment up the beach and the backwash is not strong enough to pull it back down so they tend to form berns at the top of the beach.

in winter and summer which waves frequent

winter - destructive, summer - constructive

what happens when waves approach an irregular coastline

they are refracted and increasingly take on the shape of the coastline

waves slow down in shallow water infront of a ______ because… so…

headland, friction with sea bed, so the waves in deeper water move ahead

orthogonals:

lines drawn at right angles to wave crests showing how energy is concentrated upon a headland enhancing its erosion

how are bay beaches formed

refraction sets up longshore currents that move sediment from the headlands into bays

what provides bays with sediment

longshore currents help maintain bay beaches

wave refraction at a headland diagram

what seven processes affect the coastline

• weathering

• mass movement

• erosion

• transportation

• deposition

• sedimentation

• earth movements

weathering as a coastal process

weathering on a coastline is sub-aerial and mostly operates on cliff face leading to disintegration and crumbling

mass movement as coastal process

• sub aerial

• e.g. rock falls and rotational slumping

• loosens material on cliff face as water in rocks makes them heavy and lubricates them and erosion at cliff foot undermines cliff so when conditions are right, gravity causes cliff face to collapse adding material onto beach

erosion as a coastal process

• mostly by action of waves

• marine process

• hydraulic action, cavitation, abrasion/corrasion, attrition are the main processes + solution in areas of chalk and limestone

transportation as a coastal process

• material moves up and down beach and along by longshore drift

• wave action provides energy for these movements

• tidal currents and longshore currents important

• wind moves sand up beach = sand dunes

deposition as a coastal process

• beach made by deposited material

• dynamic system as material constantly moving

• spits and tombolos produced by beach movement

• dunes made by depos. of blown sand and mudflats

• salt marshes prod. by depos. of alluvium [river silt] in river estuaries

sedimentation as a coastal process

• usually only on sea bed

• well away from coast

• large deltas can eventually produce beds of sediment

earth movements as a coastal process

• delta depos. can weigh down crust

• leads to subsidence and relative rise in sea level

• tectonic movements = uplift in land [raisd beaches]

• both = isostatic of local sea level change e.g. venice.

four ways in which waves can erode coastline

• hydraulic action

• cavitation

• corrasion

• attrition

• +solution/corrosion

hydraulic action as marine erosion

• big waves have lots of energy

• water is a dense material [one cubic metre of water weighs one ton]

• storm waves hitting sea wall or cliff foot can generate shocks of thirty+ tons per square metre

• pressure can = erosion

cavitation [form of wave quarrying] as marine erosion

• water trapped in cracks in rock is compressed by pounding of waves

• when pressure released, bubbles form in water which escape from crack w/ explosive force widening crack quickly

• air pockets compressed inside cave at high tide can weaken and quarry cave roof leading to blowhole formation

corrasion/abrasion as marine erosion

• waves throw sand, shingle and cobbles at cliff base

• effective erosion bc produces wave-cuts and notches and caves

• wave-cut platforms smoothed by this process

attrition as marine erosion

• rock falls and slumps provide material which builds up at cliff base

• wave energy moves material around and particles become smaller as they rub together

• material moved along coastline by longshore drift is susceptible to this

• pebbles become smaller and smoother as they are moved further from sediment source e.g. further from headland

solution/corrosion as marine erosion

chemicals in seawater can dissolve rocks such as chalk and limestone

marine and sub-aerial processes example

read

what weathering occurs on cool temperature coastlines

• frost shattering can be very effective as water seeps into cracks in cliff face and freezes overnight

• when liquid water turns into ice it expands by 9% which widens and weakens the crack

• repeated freezing and thawing can make the rock crumble and split.

what weathering occurs on desert coastlines

• extremes of temperature between day and night can cause expansion and contraction of the surface layers of rock on the cliff face

• the stresses caused by these changes weaken the rock and surface layers peel off

• increased availability of water at coastlines can speed up exfoliation

why does staining and crumbling happen at coastlines

• many rocks contain iron compounds

• iron oxide = rust which weakens

• decomposes rocks on cliff face

how does biological weathering happen on coastline cliffs

• cliffs often contain cracks

• halophytic/salt-loving plants can grow in these cracks widening them

how does chemical weathering occur on cliffs

• seabirds nest on ledges on cliffs away from predators

• their guano/poo is extremely corrosive

• can lead to the chemical weathering of some types of rock

how do crystals form on cliffs

• in the spray zone towards cliff bases, salt water can soak into rock pores

• when water evaporates, salt crystals form inside the rock.

• salt crystals are perfect cubes but pores are irregular

• stresses are formed as square pegs in round holes

• rock easily decomposes and crumbles

how do mass movement such as rock falls and rotational slumps occur on cliff faces

• weathering weakens rocks on cliff face by expanding cracks and disrupting rock from within

• rainwater seeping from land as through/baseflow lubricate cracks which weakens internal cohesion of rocks of cliff face

• water adds weight to rocks

• marine processes working at cliff base undermine it and remove support

what is the main mass movement in cliffs made of hard rock

rock falls, often after heavy rain

what is the main mass movement in cliffs made of unconsolidated material such as clay/glacial deposits

rotational slumping

what is cliff retreat a result of

all these processes

sources of coastal sediment diagram

read

what three sources do coastlines receive sediment from

• rivers flowing from land to sea - alluvium, most of the sediment that reaches the coastline comes from rivers

• erosion of the coast - rockfalls and slumps

• material moved on to the coastline from the sea bed - mostly by constructive waves

how does sediment move up and down the beach, how are berns, longshore bars and sand dunes formed

• swash carries material up the beach and backwash carries it back down

• waves can sort the beach material

• constructive waves move material up the beach forming berns

• destructive waves comb it downwards forming longshore bars

• wind can blow sand up beach and deposit it at top of beach forming sand dunes

suspension

fine sediment is carried as a suspension in water making it look muddy/murky

traction

larger pebbles and cobbles are rolled along the sea bed

solution

dissolved material is carried along in solution so you can’t see it

saltation

small pebbles are moved when one pebble hits another causing it to bounce which sets up a chain reaction

how does sediment move along the coastline, groynes + longshore drift

• waves arrive at an angle to the beach

• wave angle and swash direction is determined by wind direction and wave refraction

• backwash runs straight back down beach under influence of gravity

• swash and backwash operate to cause zigzag movement of material which moves it along the beach like a conveyor belt

• groynes interfere with movement of beach material by longshore drift

• deposition takes place on updrift side of obstacle making beach wider encouraging tourists and protecting coast from erosion but further along beach is starved of material and becomes thinner = increased erosion rates in downdrift areas

types of sediment, sizes & types

• cobbles

• pebbles

• shingle

• sand

• mud

where are larger sediment particles from and formed

storm beaches at the top of the beach

where are smaller sediments formed

wider, more gently-sloping loewr beach

what is sediment moved along beach by

longshore drift

when does deposition take place and where

• whenever the movement of coastal sediment slows down/stops. this happens updrift of a groyne or in sheltered locations e.g. estuary or bay.

• also where the coastline changes abruptly. spits can develop as the beach is built out across the inlet, estuary or bay

• wave refraction around an island close to coast can also lead to deposition between island and coast = cuspate tombolo

coastlines can be divided into…

sediment cells with smaller sub-cells within them

sediment movement is ______ within each sediment cell

self-contained