Coastal Systems and Landscapes Flashcards
why are coasts open systems?
it receives inputs from outside the system and transfers outputs away from the coast and into other systems
in what circumstances can coasts be considered closed systems?
during scientific research, coastline management planning, etc
what is a sediment cell?
a largely self contained stretch off coastline
how do the flows of sediment act in sediment cells?
in dynamic equilibrium
is the movement of sediment contained in sediment cells?
almost
what is dynamic equilibrium?
the maintenance of a balance in a natural system, despite it being in a constant state of change
how is the balance in dynamic equilibrium achieved?
by inputs and outputs constantly changing to maintain balance, and counteracting any changes imposed on the system
what is dynamic equilibrium in a sediment cell?
inputs and outputs of sediment are in a constant state of change, but remain in balance
how can dynamic equilibrium be upset in the long term in sediment cells?
by human interventions
how can dynamic equilibrium be upset in the short term in sediment cells?
by natural variations
when are the smaller subcells, in sediment cells, used?
when planning coastal management projects
what are positive feedback loops?
coastal system mechanisms which enhance changes within a system, taking it away from dynamic equilibrium
what are negative feedback loops?
mechanisms which balance change, taking the system back towards equilibrium
what are the 6 sediment sources?
- rivers
- cliff erosion
- wind
- glaciers
- offshore
- longshore drift
what are sediment budgets?
they use data of inputs, outputs, stores and transfers to asses the gains and losses of sediment within a sediment cell
what is the littoral zone?
the area of land between the cliffs or dunes on the coast and the offshore area that is beyond the influence of the waves
why is the littoral zone constantly changing?
short term factors like tides and storm surges, and long term factors like changes in sea level and human intervention
what is shore/shoreline?
the boundary between the sea and the land
what is offshore?
the area beyond the influence of the sea
what is onshore?
the area of land not covered by the sea, but very close to it
what is the primary source of energy for all natural sources?
the sun
what is the main energy source at the coast?
from waves which are formed offshore
when do waves occur?
when wind moves across the surface of water
how is a wave formed?
winds move across the surface of the water, causing friction drag, creating ripples and waves. Leading to a circular orbital motion of water particles in the ocean
what leads to a more horizontal movement of waves?
as the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elliptical
what happens when waves move more horizontally?
the wave height increases, but the wavelength and wave velocity both decrease
what does wave height increasing, but wavelength and velocity increasing cause?
water to back up from behind the wave until the wave breaks and surges up the beach
what is the swash?
when the wave moves up the beach
what is the backwash?
when the wave moves down the beach into the sea
what are the 3 factors affecting wave energy?
- strength of the wind
- duration of the wind
- size of the fetch
strength of wind as a factor affecting wave energy
the larger the difference between two areas the stronger the winds
duration of the wind as a factor affecting wave energy
if the wave is active for longer periods of time, then the energy of the waves will build up and increase
size of fetch as factors affecting wave energy
the larger the fetch, the more powerful the waves will be
how are constructed waves formed?
formed by weather systems that operate in the open ocean
how are destructive waves formed?
localised storm events with stronger winds operating closer to the coast
what is the wavelength of constructive waves?
long wavelength
what is the wavelength of destructive waves?
short wavelength
what is the frequency of constructive waves?
6-9 per minute
what is the frequency of destructive waves?
11-16 per minute
what are the wave characteristics of constructive waves?
low waves, which surge up the beach
what are the wave characteristics of destructive waves?
high waves, which plunge onto the beach
what are the swash characteristics of constructive waves?
strong swash, weak backwash
what are the swash characteristics of destructive waves?
weak swash, strong backwash
what effect do constructive waves have on the beach?
occurs on gently sloped beaches
what effect do destructive waves have on the beach?
occurs on steeply sloped beaches
what time of year are constructive waves dominate?
summer
what time of year are destructive waves dominant?
winter
how can constructive waves become destructive?
if a storm begins
what does the presence of constructive waves cause?
deposition on the beach
what does deposition on the beach from constructive waves lead to?
the beach profile becoming steeper
how can destructive waves become constructive?
destructive waves erode the beach, reducing the beach profile and leading to the formation of constructive waves
what is gravity as a source of energy in coastal environments responsible for?
tides which occur when the gravitational pull of the sun or moon changes the water levels of the seas and oceans
what is the tidal range?
the difference in height between the tides
where do tidal ranges tend to be the highest?
in channels
when do the highest high tides and the lower low tides occur?
when the sun and the moon are in alignment
what are rip currents?
powerful underwater currents occurring in areas close to the shoreline on some beaches when plunging waves cause a buildup of water at the top of the beach
what forms an underwater current in rip currents?
the backwashed is forced under the surface due to resistance from breaking waves
when do rip currents occur?
when the sea tide pulls water through a small area
where do high energy coastlines occur?
in areas where there is a large fetch
what are the results of high energy coastlines?
these coastlines are often eroding as the rate of erosion exceeds the rate of deposition
where do low energy coastlines occur?
in sheltered areas where constructive waves prevail
what is wave refraction?
the process bu which waves turn and lose energy around a headland on uneven coastlines.
what is erosion?
a collaborative process which involves the removal of sediment from a coastline by different types of erosion
what are the 6 main processes of erosion?
- corrasion
- abrasion
- attrition
- hydraulic action
- corrosion
- wave quarrying
what is corrasion?
sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled against the cliffs at high tide, causing cliffs to be eroded
what is abrasion?
the process where sediment is moved along the shoreline, causing it to be warn down overtime
what is attrition?
wave action cause rocks and pebbles to hit against each other, wearing each other down and becoming round and eventually smaller
what is hydraulic action?
as a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults. high pressure causes cracks to force apart and widen, these may implode under high pressure causing erosion
what is corrosion?
the mildly acidic seawater can cause alkaline rock to be eroded
what is wave quarrying?
when breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m^2.
what are the 6 factors affecting coastal erosion?
- waves
- beaches
- subaerial processes
- rock type
- rock faults
- rock lithology
how do beaches affect erosion?
if there is a beach in-front of a cliff then this will absorb wave energy and thus reduce the effects of erosion
how do subaerial processes affects erosion?
weathering and mass movement weaken cliffs
how does rock type affect erosion?
sedimentary rocks are made up of cemented sediment particles and are therefore vulnerable to erosion, where as rocks with interlocking crystals are resistant to erosion
how do rock faults affect erosion?
fissures, cracks and joints are all types of weaknesses within the rock, so the more there are, the quicker erosion of rock will occur, also increase rock face surface area, promoting erosion
how does rock lithology affect erosion?
the type and condition of rocks creation directly affects its vulnerability to erosion
what is coastal transportation responsible for?
transferring sediment within a sediment cell and between other sediment cells
what are the four main processes of transportation?
- traction
- saltation
- suspension
- solution
what is traction?
large, heavy sediment rolls along the sea bed pushed by currents
what is saltation?
smaller sediment bounces along the sea bed, being pushed by currents
what is suspension?
small sediment is carried within the flow of water
what is solution?
dissolved material is carried within the water, potentially in a chemical form
how does longshore drift use transportation to move sediment along the beach?
- waves hit the beach at direction of prevailing wind
- waves push sediment up the beach in swash
- gravity carries sediment down the beach in backwash
when does deposition occur?
when sediment becomes too heavy for the water to carry, or if the wave loses energy
what is gravity settling?
the waters velocity decreases so sediment begins to be deposited
what is flocculation?
clay particles clump together due to chemical attraction and then sink due to their high density
what is weathering?
the breakdown of rocks over time, leading to the transfer of material into the littoral zone, where it becomes an input to sediment cells
positive feedback effect on weathering?
if rate of removal of weathered rock from base of cliff is higher than the rate of weathering, then it will increase the area of exposed rock
negative feedback effect on weathering?
if removal of sediment rock from base of cliff is slower than the rate of weathering, it will lead to build up of debris at the base of the cliff, reducing the exposed cliff area and reducing rates of weathering
what is mechanical weathering?
the breakdown of rocks due to exertion of physical forces without any chemical changes taking place
what are the 3 types of mechanical weathering?
- freeze thaw
- salt crystallisation
- wetting and drying
what is chemical weathering?
the breakdown of rocks through chemical reactions
what are the 3 types of chemical weathering?
- carbonation
- oxidation
- solution
what is freeze thaw weathering?
water enters cracks in rocks and then the water freezes overnight in winter, this expands by 10%in volume, creating pressure and cracks. the makes the cliff weaker and vulnerable to erosion
what is salt crystallisation?
as seawater evaporates, salt is left behind and salt crystals grow, erecting pressure on the rock, widening cracks. salt can corrode ferrous rock due to chemical reactions
what is wetting and drying?
rocks expand when wet and the contract when drying. this frequent cycle can cause rocks and cliffs to break up.
why are rivers sediment sources?
sediment may be deposited in estuaries which are brackish (salty) areas where rivers flow into the sea
why is cliff erosion a sediment source?
cliffs erode easily, providing a significant sediment input
why is wind a sediment source?
wind is a coastal energy source and sediment transport by winds which provide sediment inputs
why are glaciers sediment sources?
in some coastal systems glaciers flow directly into the ocean depositing sediment that was stored in ice, occurring when glaciers calve
why is offshore a sediment source?
sediment is transferred to the coastal zone when waves, tides and currents erode offshore sediment sinks. the sediment is transported onto the beach, helping to build up the beach
why is longshore drift a sediment source?
sediment moves along beach with prevailing wind, which alter the direction of waves, this allows sediment to move along the coastline. the swash moves sediment up and backwash moves it back down the beach
what is biological weathering?
the breakdown of rocks by organic activity
what are the 5 types of biological weathering?
- plant roots
- birds
- rock boring
- seaweed acids
- decaying vegetation
what is carbonation?
rainwater absorbs CO^2 to. create a weak carbonic acid which reacts with calcium carbonate in rocks to form calcium bicarbonate which can be easily dissolved, causing erosion
what is oxidation?
when minerals become exposed to the air through cracks and fissures, the mineral becomes oxidised, increasing volume, causing rocks to crumble
what is solution?
when rock minerals are dissolved
what are plant roots in biological weathering?
roots of plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rock
what are birds in biological weathering?
some birds such as puffins dig burrows into cliffs, weakening them and making erosion more likely
what is rock borrowing in biological weathering?
many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face
what is seaweed acids in biological weathering?
some seaweeds contain pockets of of sulphuric acid, which if hit against a rock or cliff face, the acid will dissolve some of the rocks minerals
what is decaying vegetation in biological weathering?
water that flows through decaying vegetation and then over coastal areas, will be acidic, thus causing chemical weathering
what is mass movement?
the movement of material down a slope under the influence of gravity
what 4 main areas can mass movement be categorised in too?
- creeps
- flows
- slides
- falls
what are the 7 types of mass movement?
- soil creep
- solifluction
- mudflows
- rockfall
- landslide
- landslip or slump
- runoff
what is soil creep in mass movement?
particles rise and fall due to wetting and freezing and this causes soil to move down the slope. leads to the formation of shallow terracettes
what is solifluction in mass movement?
as the top layers thaw during summer the surface layers flow over the frozen layers, forming solifluction lobes
what are mudflows in mass movement?
an increase the water content of soil can reduce friction , leading to earth and mud flow. water can get trapped within the rock increasing pore water pressure, weakening the slope
what are rockfalls in mass movement?
occurs on sloped cliffs when exposed to chemical weathering
what are landslides in mass movement?
heavy rainfall leads to water between joints and bedding planes in cliffs which can reduce friction and lead to a landslide.
what are landslip and slumps in mass movement?
a build up in pore water pressure leads to the land collapsing under its own weight
what is runoff in mass movement?
as the water in the form of overland flow may erode the cliff face and coastal area or pickup sediment
in what environment are steep cliffs most commonly found?
in high energy environments
where are steep cliffs most common?
where the rock is strong and fairly resistant to erosion
where are gentle cliffs most commonly found?
in areas with weaker rocks which are less resistant to erosion and are prone to slumping
in what environment are gentle cliffs most commonly found?
in low energy environments
what will lead to the formation of gentle cliffs?
low energy waves, a short fetch and a large beach
what will lead to the formation of steep cliffs?
sedimentary rocks that have vertical strata are more resistant to erosion. also an absence of a beach, long fetch and high energy waves
what is the rate of retreat dependant on?
the relative importance of marine factors and terrestrial factors
which cliffs are most likely to retreat?
those made of unconsolidated rock and sands
what landform is a beach?
depositional landform
how is a beach created?
when sediment is deposited near the coastline when waves lose their energy
when does beach accretion occur?
when the beach is being built up by constructive waves, usually in summer
when does beach excavation occur?
in winter when destructive waves remove sediment from the beach
what is swash aligned?
wave crests approach perpendicular to coast so there is limited longshore drift
what is drift alignment?
waves approach at a significant angle
what are berms?
ridges which mark where the high tide line is at different times of year
what are cusps?
small curved dips in the beach where the swash comes in, and are slightly lower than the rest of the beach, creating undulations
what are runnels?
smaller ridges that are often found in smooth wet sand further towards the sea, caused by the tides
where is larger sediment found?
towards the top of the beach, where it has been left from winter storms
beach profiles and sediment types are dependant on what?
distance from the shoreline
what are spits?
a long narrow strip of land which is formed when longshore drift causes the beach to extend out to sea, usually due to change in direction of the coastline
what can the sediment projection from spits create?
a salt marsh, due to the sheltered, saline environment where water flow speed is lower, allowing deposition of finer sediments to occur
what does the length of a spit depend on?
any changing currents of rivers, which will prevent sediment from being deposited
what can cause the end of a spit to curve?
a change in wind or wave direction
what is a compound spit?
when spits have multiple recurved tips
what is a double spit?
the spits from opposites sides of a bay reach out towards each other
when does a barrier beach occur?
when a beach for spit extends across a bay to join two headlands
how does a barrier beach lead to the formation of a brackish lagoon?
water gets trapped behind it, and the brackish lagoon is separated from the sea
how have some barrier beaches formed due to rising sea levels after the last glacial period?
meltwater from glaciers deposited sediment in the coastal zone
when does a barrier beach become a barrier island?
if a barrier beach becomes separated from the mainland
where are barrier islands most common?
in areas with low tidal ranges and can be very large
what is a tombolo?
a bar or beach that connects the mainland to an offshore island
what is a tombolo formed due to?
wave refraction off the coastal island reducing wave velocity
how are sand dunes formed?
when sand deposited by longshore drift is moved up the beach by the wind
how are embryo dunes formed?
- sand trapped by driftwood or berms is colonised by plants and grass
- the vegetation stabilizes the sand and encourages more sand to accumulate there
how are mature dunes formed?
overtime, the oldest dune migrate inland as newer embryo dunes are formed (can be up to 10m high)
where do mudflats and saltmarshes form?
sheltered, low energy environments
how do mudflats develop?
as silt and mud are deposited by the river or the tide
how are mudflats colonised?
by vegetation that can survive the high salt levels and long periods of submergence by the tide
how are saltmarshes formed?
plants trap more mud and silt in a mudflat, and grudually they build up to a saltmarsh that remains exposed for longer and longer between tides
what causes channels in the surface of mudflats and saltmarshes?
erosion by tidal currents
what is eustatic sea-level change caused by?
a change in the volume of water in the sea or a change in the shape of the ocean basins
are the effects of eustatic sea-level change local or global?
global
what are the main causes of eustatic sea-level change
- changes in climate change
- tectonic movements of the earths crust and alter the shape of ocean basins
how does changes in climate change affect eustatic sea-level change?
- an increase in temperature causes melting of the ice sheets, which increases sea level
- causes water to expand, increasing sea level more
what is isostatic sea-level change caused by?
vertical movements of the land relative to the sea
-any downward movement of the land causes sea level to rise locally, while up lift of land causes sea level to fall
are the effects of isostatic sea level change local or global?
local
what are the main causes of isostatic sea level change?
- uplift or depression of the earth’s crust due to accumulation or melting of ice sheets
- subsidence of land due to shrinkage after abstraction of groundwater
- tectonic processes
what causes the sea level to vary daily?
the tidal cycle
what causes sea level to rise temporarily?
- onshore winds
- low atmospheric systems
why has global sea-level changed over a long period of time?
as temperatures start to increases, ice sheets melted and sea level rose rapidly (it reached its present level around 4000 years ago) and sea-level now fluctuates
what is global warming?
global sea temperatures increasing rapidly
what is global warming a result of?
human activities
-e.g. deforestation and burning fossil fuels
how do human activities lead to global warming?
the activities increase the concentration of greenhouse gases in the atmosphere. greenhouse gases absorb outgoing long wave radiation, so less is lost to space. as their concentration increases, more energy is trapped and the planet warms up
why are increases in temperature likely to lead to increases in sea level?
melting of ice sheets and thermal expansion of water in oceans
how many mm is global sea level rising a year?
2mm
if greenhouse gas emissions remain high, how much is the sea level predicted to increase in mm by 2100?
8-16mm
why are storms likely to become more frequent and more intense?
due to changes in ocean circulation and wind patterns
why will continued sea-level rise have major impacts on coastal areas?
- more frequent and severe coastal flooding
- submergence of low lying islands
- changes in the coastline
- contamination of water sources and farmland
how are raised beaches formed?
when the fall in sea level leaves beaches above the high tide mark
where are rias formed?
where river valleys are partially submerged
what do rias look like?
they’re wide and deep at their mouth, becoming narrower and shallower the further inland they reach
what are rias?
drowned river valleys
what are fjords?
drowned glacial valleys
what do fjords look like?
they are relatively straight and narrow, with very steep sides. They have a shallow mouth and very deep further inland
why do fjords have a shallow mouth?
caused by a raised bit of ground (called the threshold) formed by deposition of material by the glacier
how are dalmation coastlines formed?
in areas where valleys lie parallel to the coast an increase in sea level can cause them
individual landforms combine to form what?
landscapes
what is the aim of coastal management?
protect homes, businesses and the environment from erosion and flooding
what is the location of coastal management dependent on?
cost-benefit analysis
-protect large settlements and industrial siyes
what are the 4 options for coastal management?
- hold the line
- advance the line
- do nothing
- managed realignement
what is hold the line in coastal management?
maintaining the existing coastal defences
what is advance the line in coastal management?
build new coastal defences further out to sea than the existing line of defence
what is do nothing in coastal management?
build no coastal defences, and deal with erosion and flooding as it happens
what is managed realignment in coastal management?
allow the shoreline to move, but manage retreat so it causes least damage
what is hard engineering?
built structures
how does a sea wall work?
- the wall reflects waves back out to the sea, preventing erosion of the coast
- a barrier to protect from flooding
what are the disadvantages of sea walls?
- expensive to build and maintain
- creates a strong backwash which erodes under the sea wall
how does revetment work?
waves break against the revetments, which absorb the wave energy and so prevent cliff erosion
what is a revetment?
slanted structures at the foot of cliffs, made from concrete, wood or rocks
what are gabions?
rock-filled cages
-wall of gabions usually at the foot of cliffs
how do gabions work?
they absorb wave energy and so reduce erosion
what are the disadvantages of revetments?
- expensive to build
- they create a strong backwash
what are the advantages of revetments?
relatively cheap to maintain
are gabions expensive?
no, they are cheap
what is a disadvantage of gabions?
they are ugly
what are ripraps?
boulders piled up along the coast
how do ripraps work?
the boulders absorb wave energy and so reduce erosion
are ripraps cheap?
fairly cheap
what is a disadvantage of ripraps?
they can shift in storms
what are groynes?
fences built at right angles to the coast
how do groynes work?
they trap beach material transported by longshore drift. This creates wider beaches which slow the waves and gives greater protection from flooding and erosion
are groynes cheap?
quite cheap
whats a disadvantage of groynes?
they starve downdrift beaches of sand. Thinner beaches don’t protect the coast as well, leading to greater erosion and flooding
what are breakwaters?
usually concrete blocks or boulders deposited by the coast
how do breakwaters work?
they force waves to break offshore. The waves energy and erosive power are reduced before they reach the shore above
what are earth banks?
mound of earth
what are the disadvanteages of breakwaters?
- expensive
- can be damaged in storms
how do earth banks work?
they act as a barrier to protect flooding
what are the disadvantages of earth banks?
- quite expensive
- can be eroded
what are tidal barriers?
built across river estuaries and contain retractable flood gates
how do tidal barriers work?
they have retractable floodgates which can be raised to prevent flooding from from storm surges
what are the disadvantages of tidal barriers?
-VERY expensive
what are tidal barrages?
dams built across river estuaries. Their main purpose is to generate electricty
how do tidal barrages work?
water is trapped behind the dam at high tide. Controlled release of water through turbines in the dam at low tide generates electricity. They also prevent flooding from storm surges
what are the disadvantages of tidal barrages?
- VERY expensive
- they disrupt sediment flow which may cause increased erosion elsewhere in the estuary
what is soft engineering?
involves coaxing natural processes along
what is beach nourishment?
where sand and shingle are added to beaches from elsewhere
what does beach nourishment do?
it creates wide beaches, which reduce erosion of cliffs more than thin beaches
what is beach stabilisation?
reducing the slope angle and planting vegetation, or by sticking stakes and old tree trunks in the beach to stabilize the sand, also creates wider beaches
what is dune regeneration?
where sand dunes are created or restored by either nourishment or stabilisation of the sand
what does dune regeneration do?
dunes provide a barrier between land and sea, absorbing wave energy and preventing flooding and erosion
why is land use management important for dune regeneration?
the vegetation needed to stabilise the dune can easily be trampled and destroyed, leaving the dune vulnerable to erosion
what is coastal realignment (managed retreat)?
involves breaching an existing defence and aloowing the sea to flood the land behind
is soft or hard engineering more sustainable?
soft engineering
why is soft engineering more sustainable?
lower environmental impact and economic cost
what are the 2 important ideas involved in deciding how to manage coastal areas sustainably?
- shoreline management plans
- integrated coastal zone management
what are shoreline management plans?
a plan is devised for how to manage different areas with the aim of protecting important sites without causing problems elsewhere in the sediment cell
what does integrated coastal zone management do?
considers all elements of the coastal system when coming up with a management strategy. It aims to protect the coastal zone in a relatively natural state, while allowing people to use it and develop it in different ways
