Coastal systems and landscapes Flashcards
what type of system are coasts ?
open systems as it can receive inputs and transfer outputs away
- these systems may be terrestrial , atmospheric or oceanic and include rock, water and carbon cycles
note ; you may need to think of coasts as closed systems at points eg. coastal management planning
what is a sediment cell ?
coasts are split up into sections ( sediment cells ) which are boarded by prominent headlands
- within the cells the movement of sediment is contained and flows of sediment act in dynamic equilibrium
what is dynamic equilibrium ?
the balance in a natural system even though there is constant change, the system counteracts any changes imposed on it
- can be affected in the long term by human interactions or in the short term by natural variations
what are the key inputs in a coastal system ?
marine: waves, tides, salt spray
atmosphere: sun, air pressure, windspeed and direction
humans: pollution, recreation, settlement, defences
what are the key ouputs in a coastal system ?
ocean currents
riptides
sediment transfer
evaporation
what are the stores and sinks in coastal system ?
beaches, sand dunes, spits, bars, tombolo, headlands, bays, nearshore sediment, cliffs, wave cut notches, wave cut platforms, caves, arches, stacks , stumps, slat marshes, tidal flats , offshore bands and bars
what are the transfers and flows in a coastal system ?
windblown sand
mass movement processes
longshore drift
weathering
Erosion: hydrolytic action, corrosion, attrition, abrasion
Transportation: bedload, suspension, solution, traction
Deposition: gravity settling, flocculation
what is the energy in a coastal system ?
wind
gravitational
flowing water
what is a negative feedback loop ?
a mechanism that balances changes by lessening it in order to bring back equilibrium
what is an example of a negative feedback loop ?
- destructive waves loos energy and deposit sediment as an offshore bar
- the bar dissapates wave energy protecting the beach behind it
- overtime the bar is eroded not the beach
- once the bar has gone normal conditions follow and dynamic equilibrium returns
what is a positive feedback loop ?
a mechanism that enhances a change making the system more unstable and taking it away from dynamic equalibruim
what is an example of a positive feedback loop ?
- people walking over sand dune destroys the vegetation and causes erosion
- without the roots from the vegetation the rate of erosion increases
- eventually the sand dunes will be completely eroded and leaves the beach open to erosion taking it away from its original state
describe rivers as a sediment source
most of the sediment in the coastal zone is a result of input from rivers, especially after rainfall (more erosion of the bed)
- sediment may be deposited in estuaries which are salts areas where the river meets the sea
describe cliff erosion as a sediment source
areas with unconsolidated cliffs are eroded easily, as coastlines retreat sediment is inputted into the sea
the most amount of erosion occurs in winter months due to storms
describe the wind as a sediment source
the wind is a coastal energy source and can cause sand to be blown up or along a beach
sediment transport by winds may occur where there are sand dunes or desert environments
describe glaciers as a sediment source
in some coastal systems such as Antarctica or Greenland, glaciers flow directly into the ocean depositing sediment that was stored in the ice
- this occurs when glaciers calve (ice breaks off)
describe offshore stores as a sediment source
when waves and tides erode offshore sediment stores like offshore bars, sediment is transported onto the beach
sediment is also transferred from storm surges or tsunamis
describe longshore drift as a sediment source
sediment is moved along the beach due to prevailing winds which change the direction of the waves, the swash approaches the beach at an angle due to the winds transferring sediment along the beach and then the backwash pulls sediment directly backdown the beach in a zig zag. this moves sediment from one side of the beach to another
what are sediment budgets ?
similar to a carbon budget it measures the gains and losses of sediment within a sediment cell. in theory it will be in a dynamic equilibrium so inputs and outputs would be equal but due to human actions and natural variation this can shift
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
what can affect the littoral zone ?
short term factors - tides and storm surges
long term factors - changes in sea level and human intervention
what is the main source of energy for coasts ?
waves which are formed offshore, commonly generated by wind but can be made by tectonic activity or underwater landslides ( tsunami waves )
how are waves formed ?
- winds move across the surface of the water creating a frictional drag, which creates small ripples or waves
- this leads to a circular orbital motion of water particles
- as it gets shallower the orbit of partials gets more elliptical
- wave height increases and the water from the back surges forward and collapses
what factors effect wave energy ?
strength of the wind : wind is are that moves from an area of high pressure to low pressure , the greater the pressure difference ( caused by the suns heating ) the stronger winds the stronger waves
duration of the wind : if the wind is active for longer periods of time then the energy of the waves will build up and increase
size of the fetch : the fetch is the distance over which the wind blows, the larger it is the more powerful the wave
what are constructive waves ?
deposit material to create depositional landforms and steeper beaches
what are destructive waves ?
remove depositional landforms through erosion and decrease the size of the beach and make them more sloped
how are constructive waves formed ?
formed by weather systems that operate in the open ocean , the swash is stronger than the backwash and they form the beach
how are destructive waves formed ?
localised storm events with stronger winds operating closer to the coast
the swash is weaker than the backwash and material is eroded
compare the wavelength and frequency of constructive and destructive waves ?
constructive waves have a long wavelength and a smaller frequency ( 6-9 per min )
destructive waves have a short wavelength and a higher frequency ( 11-16 per min )
what are the characteristics of both types of wave ?
constructive waves are low and surge up the beach
destructive waves are high and plunge onto the beach
how might the types of waves vary ?
- in summer constructive waves are more common but in winter destructive waves are
- constructive waves may become destructive if there is a storm
- climate change may increase the storm frequency within the uk
- coastal management may affect the types of waves
how is there negative feedback with beaches and waves ?
- the presence of constructive waves causes deposition which creates a gently steeper beach
- steeper beaches mean that there will be more destructive waves
- destructive waves erode the beach reducing the profile (sloped)
- leading to more constructive waves again
which beaches do the different wave types occur ?
constructive waves occur on a gently sloped beaches
destructive waves occur on steeply sloped beaches
what are tides ?
caused by the gravitational pull of the sun or moon which changes the water levels of the seas or oceans. the difference in height between the tides is know as tidal range and tends to be largest in channels like estuaries
what are spring tides ?
when the highest high tide and the lowest low tide occur due to the sun and the moon are aligned so both there gravitational forces combine, this creates the largest possible tidal range
what are neap tides ?
the lowest high tide and highest low tide occur when the sun and the moon are perpendicular to each other, so the gravitational forces act against each other. this creates the smallest possible tidal range
what are rip currents ?
powerful underwater currents occurring in areas close to the shoreline on some beaches when plunging waves cause a build-up of water at the top of the beach, the backwash is pushed under the breaking waves and flows away from the beach
- are an energy source and lead to outputs of sediment
what are riptides ?
occur when the ocean tide pulls water through a small area such as a bay or lagoon
what are high energy coastlines ?
- more powerful waves due to a large fetch
- rocky headlands and landforms
- destructive waves
- rate of erosion exceeds rate of deposition
what are low energy coastlines ?
- less powerful waves occur in sheltered areas
- constructive waves
- rates of deposition exceed rate of erosion = deposition landforms
what is wave refraction ?
the process by which waves turn and lose energy around a headland on uneven coastlines
- wave energy is focused on headlands and dissipates in the bays creating low energy features eg. beaches
how is there a negative feedback loop associated with wave refraction ?
- a headland forms as waves don’t erode the stronger rock
- the headland then faces more erosion and the bays more deposition
- the headland eventually wares away which once again increases erosion in the bays
what is erosion ?
removal of sediment from a coastline by different types of erosion
what is corrasion ?
sand and pebbles are picked up by the sea and hurled against cliffs at high tide causing the cliffs to be eroded, the size weight and quantity of the rocks picked up effects the power of erosion
what is abrasion ?
sediment is moved along the shoreline causing it to be worn down ( sandpaper effect )
what is attrition ?
rocks and pebbles hit against each other wearing each other down so they become smaller ( doesn’t have a big effect on the coastline )
what is hydraulic action ?
as waves crash into a cliff face air is forced into cracks in the rock, the high pressure caused the cracks to force apart and widen when the wave retreats the air expands
what is cavitation ?
when bubbles in the water implode under high pressure creating tiny jets that erode the rock
what is corrosion ?
mildly acidic seawater can cause alkaline rock to be eroded, similar to carbonation weathering
what is wave quarrying ?
the breaking waves can exert a pressure on the cliff face, similar to hydraulic action
what factors effect erosion ?
waves
beaches - can absorb wave energy and reduce the effects of erosion on a cliff
subaerial processes - weathering and mass movement processes weaken cliffs, rock fragments as a result of this cause increases abrasion
rock type - sedimentary is mor vulnerable as partials can break off compared to igneous and metamorphic which are made of interlocking crystals
rock faults and characteristics
how are the different types of rocks effected by erosion ?
igneous - very slowly eroded , interlocking crystals are resistant eg, granite
metamorphic - less slowly, crystal all orientated in the same direction to resist erosion eg, slate
sedimentary - very fast eroded, lots of faults making them weak and vulnerable to erosion eg, limestone
what is traction ?
large heavy sediment rolls along the sea bed pushed by currents
what is saltation ?
smaller sediment bounced along the sea bed, pushed by currents
what is suspension ?
small sediment is carried with the flow of water
what is solution ?
dissolved material is carried within the water, potentially in chemical form
explain longshore drift ?
- waves hit the beach at an angle determined by the prevailing wind
- waves push sediment in this direction up the beach in the swash
- due to gravity the wave carries sediment back down the beach in the backwash
- this moves sediment along the beach over time
what is deposition ?
occurs when sediment becomes too heavy for the water to carry or if the wave loses energy
what are the two types of deposition ?
gravity settling - water velocity decreases so sediment begins to be deposited
flocculation - clay particles clump together due to chemical attraction and then sink due to density (process in salt and tidal marshes )
how does deposition differ in high energy coastlines and low energy coastlines ?
high energy coastlines - continue to carry the smaller sediment so larger rocks and shingle are deposited
low energy coastlines - have smaller sediment which is deposited where there is lower water velocity
what is weathering ?
the breakdown of rocks over time ( mechanical, biological, chemical ) , leading to the transfer of material into the littoral zone where is becomes an input to sediment cells
what is a positive feedback loop in weathering ?
- if the rate of removal of weathers rock form the base of the cliff is higher than the rate of weathering
- promotes further weathering as area of exposed rock is increases
- more erosion
- more rocks in water = more erosion processes like abrasion
what is a negative feedback loop in weathering ?
- if the removal of rock from the base of the cliff is slower than the rate of weathering
- build up of debris at the base of the cliff reducing the exposed area
- reduced erosion
what is mechanical weathering ?
the breakdown of rocks due to exertion of physical forces without any chemical changes taking place eg. freeze thaw, salt crystallisation, wetting and drying
what is freeze thraw weathering ?
water enters rocks in cracks and freezes, it expands in volume and this puts pressure on the rock and cracks grow
what is salt crystallisation weathering ?
as seawater evaporates salt is left behind, this puts pressure on the rock causing cracks , can also corrode some rocks
what is wetting and drying weathering ?
rocks like clay expand when they get wet and then contract when they are dry this causes cracks and frequent cycles of this cause the rocks to break
what is chemical weathering ?
the breakdown of rocks through chemical reactions
eg. solution - when rock minerals such as rock salt are dissolved
what is carbonation ?
rainwater absorbs CO2 from the air to create a weak carbonic acid with reacts with rocks and they dissolve
acid rain reacts with limestone also dissolving rocks
what is oxidation ?
when minerals become exposed to the air through cracks and fissures, the minerals become oxidised which causes them to expand and crack
what is biological weathering ?
the breakdown of rocks by organic activity
eg. plant roots growing into cracks and exerting pressure, birds burrowing into cliff cracks, seaweed acids
what is mass movement ?
the movement of material down a slope under the influence of gravity
creeps, flows, slides and falls
dependent on: cliff slope, rock type and structure, vegetation, saturation of ground, weathering
what is soil creep ?
the movement of particles downhill due to the natural rise and fall or particles due to wetting and drying
leads to formation of shallow terracettes
very slow
what is solifluction ?
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what are mudflows ?
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