Coasts Flashcards
inputs
sediment and energy
sediment: rivers, sea level rise, erosion, crushed shells, waves/tides/current transport sediment from offshore deposits
energy: winds, waves, tides, currents
outputs
sediment can be washed out to sea or deposited further along the coast
stores
landforms such as beaches, dunes and spits
flows/transfers
erosion, weathering, transportation and deposition
positive feedback
amplifies a change
negative feedback
counteracts a change
dynamic equilibrium
inputs and outputs of a system are balanced
small variations but remains balanced on average
sources of energy
wind
created by air moving from areas of high pressure to low pressure
pressure gradient between high and low stronger during storms
strong winds generate powerful waves
prevailing winds (constantly blowing in the same direction) cause higher energy waves
sources of energy
waves
created by wind blowing over the surface of the sea
friction between wind and surface creates circular motion
wave height = wind speed and fetch
friction between waves and sea bed slows them and makes their shape more elliptical
crest of wave rises then collapses
swash = up
backwash = down
constructive: low frequency, low and long, deposits sediment
destructive: high and steep, high frequency and circular cross profile, removes material from the beach
currents
general flow of water in one direction
caused by wind, variations in water temperature or salinity
move material along the coast
tides
periodic rise and fall of ocean surface caused by gravitational pull of the moon and the sun
affect the position at which waves break of the shore
area between max high tide and min low tide is where most landforms are created and destroyed
low energy coasts
low inputs of energy in the form of small gentle waves
caused by gentle winds, short fetches or gently sloping offshore zones
reef/island offshore which protects coast from full power of the waves
often have salt-marshes/mudflats
rate of deposition is higher than erosion
high energy coasts
high inputs of energy from large powerful waves
caused by strong winds, long fetches and steeply shelving offshore zones
sandy coves and rocky landforms
rate of erosion higher than deposition
sediment sources
rivers carry material from inland
sea level rise can flood valleys and form estuaries
sediment eroded from cliffs
sediment formed from crushed shells
waves tides and currents transport sediment from offshore deposits
sediment cells
(littoral cells)
lengths of coastline between two headlands that are self contained
sediment budget
the difference between the amount of sediment that enters and leaves the system
more enters = positive and builds
more leaves = negative and retreats
geomorphological processes
weathering
salt weathering
caused by saline water
saline water enters pores/cracks in rocks at high tide
tide goes out and rocks dry/water evaporates forming salt crystals. as the salt crystals form they expand exerting pressure on the rock which causes pieces to fall off
geomorphological processes
mass movement
the shifting of material downhill due to gravity
more likely to occur when cliffs are undercut by wave action, causing an unsupported overhang which is likely to collapse
can also move gradually by soil creep
unconsolidated rocks are prone to collapse as there is a little friction between particles to hold them together
heavy rain can saturate unconsolidated rocks further reducing friction and making them more likely to collapse
run off can erode fine particles and transport them downslope
geomorphological processes
erosion
a process where natural forces like water, wind, ice, and gravity wear away rocks and soil
geomorphological processes
transportation
the process of eroded material being moved
geomorphological processes
deposition
when material being transported is dropped on the coast
when sediment load exceeds the ability of the water or wind to carry it, either because sediment load increases or because wind/water slows down due to friction increasing or flows becoming turbulent
coastal processes
marine
solution
soluble rocks e.g. limestone and chalk get gradually dissolved by sea water
coastal processes
marine
attrition
bits of rock in the water smash and grind against each other and break into smaller bits
coastal processes
transportation
traction
very large particles e.g. boulders are pushed along the sea bed by the force of water
coastal processes
transportation
suspension
very fine material such as silt or clay particles s whipped up by turbulence and carried along in the water
most eroded material is transported this way
coastal processes
transportation
solution
substances that can dissolve are carried along in the water e.g. limestone is dissolved into water that’s slightly acidic
coastal processes
transportation
saltation
larger particles such as pebbles/gravel are too heavy to be carried in suspension. instead the force of the water causes them to bounce along the sea bed
longshore drift
swash carries sediment up the beach parallel to the prevailing wind and backwash carries sediment back down the beach at right angles to the shoreline
when there’s an angle between the prevailing wind and the shoreline a few rounds of swash and backwash move sediment along the shoreline
geomorphological processes
mass movement
types
slides: material shifts in a straight line
slumps: material shifts with a rotation
rockfalls: material breaks up and falls
mudflows: material flows downslope
geomorphological processes
weathering
freeze thaw weathering
occurs in areas where temperatures fluctuate above and below freezing
water enters joints and crevices in rocks
temp drops below 0, water in cracks freezes and expands
overtime repeated freeze thaw action weakens the rocks and causes pieces to fall off
coastal processes
transportation
deposition
when material being transported is dropped on the coast
when sediment load exceeds the ability of the water or wind to carry it, either because sediment load increases or because wind/water slows down due to friction increasing or flows becoming turbulent
run off
the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earth’s surface.
the primary agent in soil erosion by water
landforms of erosion
headlands and bays
formed on discordant coastlines
where there are bands of alternating hard rock and soft rock and right angles to the shoreline
soft rock is eroded quickly forming bays and the harder rock is eroded less and sticks out as a headland
landforms of erosion
blow holes
sea caves along the shore can have an opening in the ground above. when waves enter the sea cave with sufficient force, water can travel upward with great pressure and escape through the opening
landforms of erosion
caves, arches and stacks
cliff profile features
weak areas in rocks are eroded to form caves
caves on opposite sides of a narrow headland may eventually join up to form an arch
when an arch collapses it forms a stack
landforms of erosion
cliffs and wavecut platforms
cliffs form as the sea erodes the land and over time they retreat due to the action of waves and weathering
weathering and wave erosion cause a notch to form at the high water mark, this eventually turns into a cave
rock above the cave becomes unstable with nothing to support it and collapses
wave cut platforms are flat surfaces left behind when a cliff is eroded
landforms of deposition
beaches
form when constructive waves deposit sediment on the shore
landforms of deposition
spits
simple
tend to form when the coast suddenly changes direction
longshore drift continues to deposit material across the river mouth leaving a bank of sand and shingle sticking out into the sea
landforms of deposition
offshore bars
bars are formed when a spit joins two headlands together across a bay or a river mouth
a lagoon forms behind the bar
offshore bars form off the coast when material moves toward the coast and may remain partly submerged by the sea
landforms of deposition
barrier islands
long narrow islands of sand/gravel that run parallel to the shore and are detached from it, tend to form in areas where there’s a good supply of sediment, a gentle slope offshore, powerful waves and a small tidal range
landforms of deposition
sand dunes
formed when sand deposited by longshore drift is moved up the beach by the wind
sand trapped by driftwood/berms is colonised by plants/grasses, the vegetation stabilises the sand and encourages more to accumulate there
overtime oldest dunes migrate inland
estuarine mudflats and saltmarshes
formed in sheltered, low energy environments
silt and mud are deposited by the river or tide mudflats develop
mudflats are colonised by vegetation that can survive high salt levels and long periods of submergence
plants trap mud and silt and build upwards to create an area of saltmarsh that remains exposed for longer and longer between tides
eustatic sea level change
caused by a change in the volume of water in the sea or by a change in the shape of the ocean basins
global effects
main causes: 1) climate change (increase or decrease in temp causes melting/formation of ice) 2) tectonic movements that alter the shape of ocean basins, e.g. sea floor spreading increases volume of basin so decrease sea level
isostatic sea level change
caused by vertical movements of the land relative to the sea
downward movement of land causes sea level to rise locally whilst uplift of land causes sea level to fall
effects are local
causes: 1) uplift/depression of earths crust due to accumulation/melting of ice sheets or accumulation of sediment, 2) subsidence of land due to shrinkage after abstraction of groundwater, 3) tectonic processes e.g. one plate forced under another
major sea level change in the last 10,000 years
last glacial period (110,000 to 12,000 years ago) water was stored in ice sheets so sea level was lower than present, last glacial maximum sea level was 130m lower than present
temps began to increase 12,000 years ago ice sheets melted and sea level rose rapidly and reached its present level around 4000 years ago
over last 4000 years has fluctuated around present value but been rising since about 1930
coastlines of emergence
when sea level falls relative to the coast, new coastline emerges from the sea
this creates different landforms:
raised beaches: when the fall in sea level leaves beaches above the high tide mark. over time beach sediment becomes vegetated and develops into soil.
wave cut platforms
relict cliffs: cliffs no longer eroded by the sea and slowly covered by vegetation
wave cut notches, caves, arches and stacks within relict cliffs
e.g. falmouth
coastlines of submergence
rias
formed when river valleys are partially submerged
gentle, long cross profile
wide and deep at the mouth
becoming narrower and shallower further inland
processes create and alter landforms and landscapes over time
individual landforms combine to form landscapes
coastal landscapes can be dominated by processes of deposition or erosion but most are formed by both
processes can change/create landforms which means coastal landscapes change over time
e.g. a change in one factors can lead to a change in others e.g. a change in wave direction may increase deposition and eventually change a landscape dominated by erosive landforms to one dominated by depositional landforms and 2) relict landforms can still experience coastal processes
coastal landscapes therefore often made up of a mixture of active and relict landforms that reflect different periods of change
changes occur over a range of temporal and spatial scales
recent physical and socioeconomic impacts of climate change on coasts
2mm sea level rise each year
predicted physical and socioeconomic impacts of climate change on coasts
8-6mm rise per year by 2100
frequent and intense storms
more frequent and severe coastal flooding
submergence of low lying islands e.g. maldives
changes in the coastline e.g. bangladesh lost
contamination of water sources and farmland, saline water damage ecosystems and crops and make water unsuitable for use
increase coastal erosion
human causes of climate change
deforestation and burning of fossil fuels increasing the greenhouse effect
physical causes of climate change/sea level change
global warming =
melting of ice sheets
thermal expansion
four options for coastal management
hold the line
advance the line
do nothing
managed retreat
hard engineering
sea walls
reflects waves back out to sea preventing erosion
barrier to flooding
expensive to build and maintain
creates a strong backwash which erodes under the wall
hard engineering
revetments
slanted structures built at the foot of cliffs
absorb wave energy
expensive to build, cheap to maintain
create a strong backwash
hard engineering
rip rap
boulders piled up along the coast absorb wave energy
fairly cheap
can shift in storms
hard engineering
gabions
rock filled cages
cheap
ugly
hard engineering
groynes
fences built at right angles to the coast that trap beach material transported by longshore drift which gives protection to flooding and erosion
quite cheap
starve down drift beaches of sand
hard engineering
barrages
dams built across river estuaries to generate electricity
very expensive
disrupt sediment flow
soft engineering
beach nourishment
sand and shingle added to beaches from elsewhere
creates wider beaches and reduces erosion of cliffs
soft engineering
dune regeneration
where sand dunes are created or restored by nourishment or stabilisation of the sand
absorbs wave energy creating barrier between land and sea
soft engineering
marsh creation
planting appropriate vegetation which stabilises sediment which reduces the speed of waves which reduces erosive power and flooding
soft engineering
land use management
important for dune regeneration to keep vegetation in tact
wooden walk ways and fenced off areas
sustainable management strategies
shoreline management plans
plan devised for each sediment cell with the aim of protecting important cites without causing problems elsewhere in the cell
can hold, advance, retreat the line or do nothing
all local authorities in one call cooperate
sustainable management strategies
integrated coastal zone management
considers all elements of the coastal system
aims to protect the coastal zone in a natural state while allowing use and development
integrated: environment viewed as a whole, different uses are considered and local, regional and national levels of authority all have input
dynamic strategy
geomorphological processes
weathering
wetting and drying
when rocks containing clay get wet the clay expands and the pressure caused by this breaks fragments off the rock
geomorphological processes
weathering
chemical weathering
the breakdown of rock by changing its chemical composition
e.g. carbon dioxide in the atmosphere dissolves in rainwater forming a weak carbonic acid. this acid reacts with rock that contains calcium carbonate e.g. limestone so the rocks are gradually dissolved
coastal processes
marine
hydraulic action
air in cracks in cliffs is compressed when waves crash in
the pressure exerted by the compressed air breaks off rock pieces
coastal processes
marine
wave quarrying
the energy of a wave as it breaks against a cliff is enough to break pieces off
coastal processes
marine
corrasion/abrasion
bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces.
coastal processes
marine
cavitation
as waves recede the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off
landforms of deposition
spits
compound
occasional changes to the dominant wind and wave direction may lead to a spit having a recurved end
overtime several recurved ends may be abandoned as the waves return to their original direction, a spit with multiple recurved ends is called a compound spit
landforms of deposition
beaches
shingle
steep and narrow made up of larger particles which pile up at steep angles
landforms of deposition
beaches
sand
formed from smaller particles, wide and flat
landforms of deposition
beaches
berms
ridges of sand and pebbles about 1-2m high found at high tide marks
landforms of deposition
beaches
runnels
grooves in the sand running parallel to the shore formed by backwash draining to the sea
landforms of deposition
beaches
cusps
crescent shaped indentations that form on beaches of mixed sand and shingle
landforms of deposition
tombolos
a bar that connects the shore to an island
e.g. st ninians isle in the shetland islands is joined to a larger island by a tombolo
coastlines of submergence
fjords
drowned glacial valleys
straight and narrow
steep sides
shallow mouth but very deep further inland
coastlines of submergence
dalmatian coastlines
where valleys lie parallel to the coast, an increase in sea level can form a dalmatian coastline
the valleys are flooded leaving islands parallel to the coastline
e.g. croatia
landforms of deposition
spits
behind the spit
behind the spit is sheltered from waves and often develops into mudflats and saltmarshes
