Coastal landscapes and systems Flashcards
How can coasts be classified?
- geology (including lithology and structure, concordant and discordant)
- sea level changes (submergent or emergent)
- level of energy (high or low energy coastline)
- the dominant coastal process (landforms of erosion/deposition, sediment inputs)
what are the long-term criteria for categorising coasts?
- geology - sea level changes
what are the short-term criteria for categorising coasts?
- level of energy - sediment inputs (sediment added through deposition and removed by erosion)
explain the structure of the littoral zone including some features
coast backshore (storm beach) foreshore (pebbles + berms) nearshore (runnels and ridges) offshore
what is the littoral zone?
the boundary between land and seas and is the area of shoreline where land is subject to wave action. it is subdivided into: back shore, foreshore, nearshore and offshore
why does the littoral zone vary?
due to short-term factors and long-term factors
what are the short-term factors affecting the littoral zone
individual waves, daily tides, seasonal storms
what are the long-terms factors affecting the littoral zone
changes to sea levels, climate change
what areas of the littoral experience the most human activity?
the back shore and foreshore experience the most human activity
what is the overall word to describe the state of the littoral zone?
DYNAMIC. because of the dynamic interaction between the processes operating in the seas, oceans and on land.
what is the coastal system
inputs into process and then to outputs
what are inputs in a coastal system
- marine: waves, tide, storm surges - atmospheric: weather and storm surges - land: rock type, tectonic activity - people: human activity and coastal management
what are processes in a coastal system
- weathering - mass movement - erosion - transportation - deposition
what are outputs in a coastal system
- erosional landforms - depositional landforms - different types of coasts
explain Cornwall’s geology
Cornwall bears the worst of the weather from the Atlantic ocean but due to is geology, its rocky coastline can withstand frequent storms. much of Cornwall consists of: - igneous rock (such as basalt and granite) - older compacted sedimentary rocks (sandstone) - metamorphic rocks (slates)
explain what rocky coastlines are like
- areas of high or low relief which usually form in areas with resistant geology in high energy environments, where erosion is greater than deposition - destructive waves - tend to be stretches of the Atlantic-facing coast, where waves are powerful
explain what coastal plains are like
- (sandy and estuarine coastlines) at low reliefs - where the rate of deposition exceeds the rate of erosion - they result from the supply of sediment from different terrestrial and offshore sources, often in a low-energy environment - constructive waves, form sand dunes, beaches, mudflows and salt marshes - tend to be stretches of the coast where waves are less powerful or where it is sheltered from large waves, can form by sea level changes
what is the word for a supply of sediment?
coastal accretion
what are terrestrial sources of sediment?
from mass movement or rivers
what are offshore sources of sediment?
from waves or currents
what is the difference between rocky or cliffed coastlines vs coastal plain landscapes?
rocky or cliffed coastlines: when there is a clear distinction between land and sea, mainly because of the height of the cliffs. mainly in the north west , occupy 1000km of the UK’s coastline coastal plain landscapes: where the land slopes gently towards the sea and there is an almost imperceptible transition form one to the other. these are often maintained in a state of dynamic equilibrium from the sediment coming in and out. the wash is the largest estuary system in the UK, mainly in the east and south fo England.
are coastlines always either high or low energy?
no. many coastlines are a mixture of big and low energy environments. for examples, areas such as holderness which hare predominantly low energy can experience short-term high energy erosion through winter storms.
explain dynamic equilibrium
where erosion = deposition. there is a continuous flow of energy and material through the coasts but the size of stores (beach, salt marsh) remains unchanged
what is geological structure?
refers to how the rock is arranged on a macro-scale and looks at the arrangement of different rock types in relation to each other. It looks at the rock strata, deformation and presence of faulting.It looks at the rock strata, deformation and presence of faulting.
what are concordant coastlines?
- this is where rock starts runs parallel to the coast forming bays and coves - example: the souther coast of the isle of purbeck has formed lulworth cove and kimmeridge bay due to its concordant structure
what are discordant coastlines?
- this is where the rock starts runs perpendicular to the coast forming headlands and bays - example: the isle of Purbeck’s eastern coast leading to headlands at peril point and durlston head, swanage bay has formed
explain the formation of Dalmatian coasts
1) tectonic activity folded limestone layers so that ridges (anticlines) and valleys (synclines) formed parallel to the coast 2) sea level rose following the end of the ice age and drowned the valleys (creating a submergent coastline) 3) the tops of the ridges remained above the surface of the sea running parallel to the coast an example of this is the Croatian Dalmatian coast
explain the formation of haff coasts
1) the build up of these sand dunes have created lagoons (haffs) between them and the shore 2) they form where deposition produces unconsolidated geological structures parallel to the coastline 3) this forms long sediment ridges topped by sand dunes that run parallel to the coast an example is chesil beach in Dorset which has formed in this way. shingle ridge reconnected island of portland bill to land (a tombolo)
what are half coasts?
they are long spits of sand and lagoons aligned parallel to the coast
what is beach morphology?
the shape of a beach including width and slope (profile) and other features such as berms
explain the formation of headlands on discordant coastlines
1) wave action erodes the less resistant rock quicker due to hydraulic action and abrasion 2) the more resistant rock is left sticking out as a headland, causes waves to refract and as water becomes shallower and so waves energy is concentrated on the headlands and waves become higher increasing erosive power on the headland 3) the bay becomes sheltered as wave energy is dissipated, results in the formation of beaches as sediment is deposited in the low energy environment
what does the morphology of discordant coasts lead to
the altering of the distribution of wave energy and rate of erosion through wave refraction
explain swanage bay
- on the isle of purbeck in east dorset - formed by the erosion of less resistant Wealden clays - resistant limestone forms perril point headland to the south projecting out by 1km and the resistant rock forms the foreland headland which projects 2.5km to the north - structure is not the only factor influencing the indentation of swanage bay. since it faces east it is sheltered from the prevailing south westerly winds and highest energy waves
what are cliff profiles influenced by?
- geology, especially the resistance to erosion of the rock
- the dip of rock strata in relation to the coastline
explain joints
- (vertical cracks), these are fractures caused either by contraction as sediments dry out or by earth movements during uplift - they are fractures created without displacement and occur in most rocks, dividing rock strata up into blocks with a regular shape - jointing increases erosion rates by creating fissures which marine erosion processes such as HA can exploit example: in bantry bay, the limestone is heavily pointed, leading to more rapid fluvial and marine processes in adjacent sandstones
explain faults
- formed when he stress of pressure not which a rock is subjected, exceeds its internal strength (causing it to fracture). the faults then slip along fault planes. - it significantly increases erosion since faulted rocks are much more easily jointed - huge forces are involved in faulting and displacing them and therefore either side of the fault line, rocks are often heavily fractured example: in bantry bay in cork in the republic of Ireland there is a major fault which runs SW-NE down the centre of the bays. the limestone is weakened allowing rapid fluvial erosion
explain folds
- they are bends in rocks formed by pressure during tectonic activity which makes rocks buckle and crumple - the main two types are anticlines and synclines - folden rock is often more heavily fissured and jolted, meaning they are more easily eroded, also increases erosion by increasing angle of dip and causing joins through the stretching along anticline crests an compressed in syncline troughs
explain dips
- refers to the angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland) - its a tectonic feature, sedimentary rocks deposited horizontally can be tilted by faulting and folding by tectonic forces
what is horizontal dipping
a vertical or near-vertical profile, notches reflect weathering and small scale mass movement
what is a high angle of seaward dip
produces a sloping, low-angled profile with vulnerable rock layers, loosened by weathering
what is a low angle of seaward dip
produces a steep profile that may even exceed 90 degrees, creating areas of overhanging rock, vulnerable to rock falls
what is landward dipping strata?
produces steep profiles on 70º-80º as downward gravitational force pulls loosened blocks into place, very stable with few rock falls
what is a cliff profile?
the height and angle of a cliff face, plus its features such as wave cut notches or changes in slope areas
what are micro features?
- small-scale features such a scales and wave-cut notches which form part of a cliff profile - the location of these micro-features are often controlled by the location of faults and/or strata which have a high amount of joints and fissures
what is the relief of an area affected by?
the relief or height and slope of land is also affected by geology and geological structure. there is a direct relationship between rock type, lithology and cliff profiles
explain the different stages of a cliff profile
what is lithology?
refers to the physical characteristics of the rock. igenous, metamorphic, sedimentary and unconsolidated rock each have different characteristics.
it also influences geological structure on a meso (medium scale) and micro scale (some types of rocks are more likely to have joints and bedding planes)
how does lithology affect resistance?
1) mineral composition
2) rock type
3) structure
how does mineral composition affect resistance?
- some rocks contain reactive minerals eaisly broken by chemical weathering, e.g. calcite in limestone
- other minerals are more inert that chemically weather more slowly
how does rock type affect resistance?
- sedimentary rocks are clastic (sediment particles compacted together) and these are often reactive and easily chemically weathered
- igneous rocks are crystalline with strong chemcial bonding
- rocky coasltines differ in resistance
how does structure affect resistance?
rocks with fissures or air spaces erode more easily
what are rates of recession influenced by?
it is influenced by bedrock lithology (I,S,M) and the geology
- how reactive minerals in the rock are when exposed to chemical weathering
- whether rocks are clastic (less) or crystalline (more resistant)
- the degree to which rocks have cracks, fractures and fissures
give examples of areas from the most resistant rock to the least resistant rock
most resistant: IGNEOUS- Land’s End, South Cornwall (granite)
resistant rock: METAMORPHIC- St Ives, Cornwall (slate)
resistant sedimentary rock: SEDIMENTARY- Blackers hole, south Purbeck, Dorset (Limestone)
least resistant rock: Holderness, NE Coast, (boulder clay)
explain igneous rocks
- their crystalline structure (interlocking cystals) means they are well connected and impermeable with few lines of weaknesses (resistant)
- these rock types create rocky coastlines with steep profile cliffs
- erosion rates: 0.1-.0.3 cm/yr
- e.g. granite, basalt
- example: lands end, Cornwall (granite)
explain metamorphic rocks
- they are also well-connected and impermeable
- however they are often folded and faulted so have weaknesses
- these rock types create rocky coasltines with steep profile cliffs (depending on folding and dip) and erode slowly
- erosion rates: 0.5-1 cm/yr
- e.g. marble, slate, schist
- crystalline rocks are resistant to erosion
- example: St Ives, Cornwall (slate)
explain sedimentary rocks
- they are clastic meaning they are made up of cemented sediment particles rather than interlocking crystals
- formed in stratas (layers) with joints which provides weaknesses and makes limestone permeable along with other jointed sediemntary rocks whereas other ones are porous due to the presence of air spaces
- rocks that are younger erode faster than the others as they are softer and weaker, older sediment is buried deeper and is subject to more intense compaction with stronger sedimentation- making them more resistant
- limestone erosion rates: 1-2cm/yr, chalk erosion rate: 1-100 cm/yr
- example: Old Harry, Purbeck, Dorset (chalk)
explain unconsolidated sediment
- they are the least resistant, they are not cemented together in anyway so are very vulnerable to erosion, fast recession rates
- can create slumped coastlines due to mudslides/landslides causing slumping
- the boulder clay of Holderness coast in Yorkshire retreats at a rate of 2-10 m p.a
- boulder clay erosion rates: 100-1000 cm/yr, sandstone rate: 10-100 cm/yr
what are the factors influencing the rate of recession?
- geology
- lithology
- weathering
- mass movement
what is differential erosion?
where cliffs are composed of differing lithology, leads to different sections of a cliff eroding/receding at different rates. it can also be produced when there are alternating permeable and non-permeable strata
they may form a ‘bench’ feature at the cliff base and further up overhanging sections until they collapse by mass movement.
however, the overall rate of recession is determined by the resistance of the weakest rock layer
what are the 4 different examples of differential erosion?
- a spring creating erosion and saturation leads to slumping
- poor water pressure leads to slumping
- wave-cut notches from different rates of erosion
- resistant rock creating a bench feature at the cliff base
explain a spring creating erosion and saturation leading to slumping for differential erosion
when groundwater flows through the permeable sands but cannot flow through the impermeable clay which leads to the permeable layer becoming saturated, weakening it and causing slumping
explain poor water pressure leading to slumping in differential erosion
poor water pressure (the internal force within cliffs exerted by groundwater) in the saturated layers pushes rock particles apart, reduces friction and lubricates lines of weaknesses
explain the formation of wave-cut notches in differential erosion
wave cut notches are created by erosion of the weak coal layer with more resistant siltstone overhanging the coal below
explain the importance of permeability in differential erosion
permeable rocks allow water to pass throug them. groundwater flow through permeable rock can weaken the rock by removing the cement that binds the rock sediment. slumping is a common outcome.
what are the two types of cliff profiles
1) steep, unvegetated cliffs
2) shallow-angled, vegetated cliffs
explain steep, unvegetated cliffs
- produced where marine erosion dominates
- there is little or no debris at the base as it is broken by attrition and transported offshore or along the coast
explain shallow-angled, vegetated cliffs
- they have a convex profile (curved like the interor of a circle)
- there is debris at the base becuase sub-aerial processes slowly move sediment downslope, but marine erosion is unable to rmeove it from base
- produced where there is little active marine erosion
what is succession?
the changing structure of a plant community overtimes as an intially bare surface is colonised by pioneer species and continues to develop
explain the role of vegetation in stabilising sediment
- vegetation can stabilise unconsolidated sediment and protect it from erosion
1) plant roots bind together, making it harder to erode
2) plant stems and leaves covering the ground surface protect sediment from wave erosion and from tides and currents when exposed at high tide
3) prevent sediment from wind erosion at low tide
4) plant stems interrput the flow of water and wind, encouraging deposition and when the vegetation dies it adds its organic matter (humus) into the soil
what are pioneer plants?
- these are the first plants to colonise freshly deposited sediment
- they being the process of plant succession, during which other species and take over until a balance is reached, the changes allow other species to colonise
- they modify the environment by: stabilising sediment, adding organic matter that retains moisture and reduces evaporation in sand
explain the pioneer plant present in sand dunes: marram grass
- xerophyte
- has extremely long roots which binds the dune together, up to 3m long
- it has rhizomes which helps it keep anchored into the ground
- holds the beach together, allows the dune to develop as it builds up dense vegetation
- leaves roll inwards to kepp in moisture
- when it dies out, it adds lots of organic matter in the soil, leading to further plant growth
explain the pioneeer specie in salt marshes: glasswort
- when submerged, plants provide a protective layer so the sediment is not directly exposed to erosion by the tide
- succulent stems to store water, continues to grow
- dead organic matter is added to the sediment and helps to create soil which is less vulenrable than loose sediment
- halophyte as it may be on higher levels, lack water
what are halophytes and xerophytes?
halophytes- salt-tolerant species
xerophytes- drought-resistant species
what is each stage in plant succession called and what si the end stage called?
a seral stage
the end result is called a climax community
what are sand dunes?
an accumulation of sand grains shaped into mounds and ridges by the wind in coastal areas
what is plant succession on sand called?
psammosere
what are the sections of a sand dune called?
embryo dunes
fore dunes
yellow dunes
grey dune
dune slac
mature dunes (climax community)
explain plant succession on a sand dune
1) there is a plentiful supply of sand, a large area for sand to dry out and onshore winds to that blow sand landwards. sand accumulates to form an embryo dune.
2) pioneer species like marram grass colonise the dune, stabilising it and helps to trap more sand
3) a fore dune develops when enough sand has been trapped an the dune starts to become more stable
4) now an established dune will become more vegetated by marram grass which provides organic matter to the sand and soil to devleop, improving the conditions
5) with soil now developed on the dune, it becomems a grey dune. this is permanent and conditions ar suited to a greater variety of species including heather and gorse
6) between dunes, dune slack develops. wind erosion can deepen them and they may be waterlogged in high tide conditions.
7) furthest inalnd is the climax community. there the soil is fully developed and the dune is fully stabilised and biodiversity is at its highest, trees can grow (birch)
how do the types of plants change during psammosere
at first, the succession starts with halophytic plants capable of growing in salty, bare sand. as they trap more sand it develops into an embryo dune that alters the environmental conditions to one where xerophytic plants can flourish
what is plant succession called on salt marshes
halosere
what are ideal areas for salt marshes to form
estuarine areas are ideal for salt marshes as theyre sheltered from strong waves (so sediment like mud and silt can be deposited) and rivers transport sediment to the river mouth which can be added by seidiment flowing into the estuary at high tide.
they form in low energy environments ir estuaries, sheltered bays and behind spits. rivers bring fine muds and silts and tidal conditions bring other sediments, all of which are deposited.
explain plant succession along salt marshes
1) the mixing of fresh water and sea water causes clay particles to stick together and sink which is called flocculation. this areas is colonised by algae which have to survive being submergeed twice a day.
2) the algae helps to trap more seidment and builds the height of the marsh, making it suitable for other species. species are halophytic and include cordgrass and glaswort
3) sediment becomes more stable and vegetation adds dead organic matter, making conditions better for plant growth. conditions become less salty as the marsh is now only submerged occasionally (spring tides)
4) at the inland end of the marsh, soil has developed and he climax community is established (trees)
what are blowouts?
they are created when storm events erode sections of the yellow dune through wind or wave erosion. however, over time, deposition of sediment and recolonisation of vegeation will rebuild the dune’s damaged areas.
how are waves created?
waves are created through friction between the wind and water surface, transferring energy from the wind into the water. this generates ripples, which grows into waves whedn the wind is sustained.
what does wave size depend on?
- the strength of the wind
- how long has the wind been blowing for
- the length of the fetch
what is the fetch?
this is the uninterrupted distance across water over which the wind blows and therefore the distance waves have to grow in size
which area suffers the greatest waves?
the southwest due to the long fetch along the atlantic
explain wave formation and the breaking of waves
1) waves move across open ocean in circular motion as ocean swell
2) as the waves reach shallower water, when their wave height is less than half the wavelength then friction increases slowing the wave down for the circular oscillations to become more so elliptical
3) as the wavelength decreases due to the shallower water, wave height increases and eventually the wave breaks as the top of the wave is moving faster than the base
4) the waves then lose enrgy and gravity pulls the water back as backwash
what are destructive waves like?
- they degrade a beach
- high waveheight, low wavelength
- backwash > swash
- drags sediment back to sea
- scours beach
- 13-15 break/minute
- high energy
- causes cliff retreat
- plunging breaker
- steep beach
what are constructive waves like?
- they aggrede a beach
- low waveheight, long wavelength
- swash > backwash
- brings sediment back to the sea
- builds beach up
- 6-8 break/minute
- low energy
- spilling breaker
- flat beach
what are swell waves like?
- waves formed by winds blowing over larger distances, they travel out of windy and stormy areas
- swell waves originate in mid-ocean and maintain their energy for thousands of miles
- is an ocean wave system not raised by the local wind blowing
- as swell waves advance, its crest becomes flattened and rounded and its surface smooth
using cliff profiles explain how recession rates can differ
- recession rate increases if dip is towards so as weathering opens joints and gravity speeds mass movement
- steep dip to the sea increases erosion rate as gravity makes bedding planes unstable and slabs slide downslope. this increases recession rates
- a cliff with landward dipping bedding planes are relatively steep and stable whcih decreases recession rates
- landward dip with well-developed joints will increase recession rates as joints acts as slide planes
what are the 4 erosional processes explained
abrasion- the rubbbing together of hard load, sand paper effect
attrition- rocks bashing into one another breaking them down
hydraulic action- air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face. when the wave retreats, pressure is released explosively which can widen cracks and dislodge blocks friom the cliff face
solution- where water in waves dissolves rock minerals
how are erosional processes influenced by wave type, size and lithology?
- most effective during high energy storm events with large destructive waves
- most effective in winter, in high energy storms
- faster when the tide is high
explain the cave-arch-stack-stump sequence
- the headland protrudes out into the sea as it is more resistant which means wave energy is concentrated on it due to wave refraction
- wave action attacks weaknesses in the headland due to abrasion and hydraulic action leading to cavitation
- this widens cracks into crevices and into caves
- caves can be eroded to form blowholes as the ceiling collapses
- marine erosion deepens the caves until they connect up and an arch is created and erosion continues and the roof of the arch becomes unstable from the widening of the arch due to weathering and other sub-aerial processes
- the arch eventually collapses by blockfall to form a stack
- continual undercutting and HA in the joints at the base of the stack creating a stump like Old Harry’s wife
explain the formation of old harry rocks
- wave refraction concentrates wave action on the headlnad, hydraulic action and abrasion slowly erodes the headland to form a series of landforms
1) chalk headland leads to wave refraction
2) deposited sand from nearby waters deposit to form beaches
3) waves carved into rock to form chalk cliffs, undercut to form hollow until it becomes so unstable that it collapses
4) pockets of air are compressed into the cracks with the water that it becomes unstable and falls
5) wave quarrying forms arches
what are blowholes?
- caves can partially collapse to produce a hole in the cliff
- waves hitting the base of the cliff can be forced through and sprout water at the top
how do cliffs vary in morphology?
they vary in their morphology depending on lithology and weathering are actively eroded by wave action or they are affected by sub-aerial processes
explain the formation of a wave-cut platform
1) wave action at the base of the cliff between high and low tide means that hydraulic action and abrasion undercuts the clif to form a wave cut notch
2) this continues and the cliff above the notch is left unsupported and eventually collapses
3) the cliff retreats leaving a wave cut platform which is the base of the cliff that is left
4) this process maintains a steep cliff profile
what is a wave-cut platform?
it is a flat rock surface exposed at low tide, extending out to sea from the base of a cliff
what is a wave cut notch?
a curved indentation of about 1-2m high extending along the base of a cliff. it forms between the high and low tide marks, where destructive waves impact against the cliff.
what are beach profiles like in summer?
- they are steeper in summer, where constructive waves are more common than destructive. wave energy dissipates and deposits over a wide area.
- as the berm builds up, the backwash becomes weaker and only has enough energy to move smaller material, so the beach material becomes smaller towards the shoreline
what are beach profiles like in winter?
- destructive waves occur at a hgiher frequency
- berms are eroded by plunging waves and high-energy swash
- strong backwash transports sediment offshore (offshore bars are made)
- destructive, high-energy waves dominate in the winter, lowering angle of beach profile and spreading shingle over the whole beach
how does the size of sediment vary on a beach?
as constructive waves have a weaker backwash can only transport smaller particles down the beach. this leads to the sorting of material with larger, heavier shingle at the back of the beach and the sand drawn back closer to the sea. the backwash only has enough energy to transport down smaller sediment. they also become more angular at the back of the beach and rounder at the front of the beach.
what influences beach morphology?
1) sediment supply- if the supply is reduced from rivers, for example, due to the construction of dams on rivers that traps sediment upstream
2) human interference- often a result of coastal management in one place having an effect on processes further along the coast
3) climate change- if global warming made the UK climate on average stprmier, then destructive waves and ‘winter’ beach profiles would become more common
explain morphology along cliff profiles
- storm beaches result from high-energy deposition of very coarse sediment during the most severe storms
- berms typically of shingle/graves, result from summer swell wave deposition
- the middle area of the ebach is mainly sand, but the sand is coarser where berms/ridges have been deposited than in chsnnels and runnels
- offshore ridges formed by destructive wave erosion and subsequent deposition of sand and shingle offshore.
why is sediment constantly moving at the coast?
as a result of waves, tides and currents. the main process is LSD.
what are the 4 methods of transportation?
traction- where large, heavy load items are rolled along the sea bed
saltation- where lighter sediment bounces along
suspension- where very light sediment is carried within a body of water or air
solution- where seidment is carried dissolved within the water
explain the process of longshore drift
- the prevailing winds (in this case SW) mean that the waves approach the coastline at an angle
- this means the swash moves sediment up the beach at the same angle but backwash moves sediment straight down the beach under gravity
- waves carry large pebbles by rolling them (traction) and small pebbles by bouncing them (saltation) and sand, silt and clay is suspension
- as the process continues, sediment is moved east and over time, a drift aligned beach will form.
what are swash-aligned beaches?
waves approach the coasltine perpendicular to the beach. the swash and backwash move sediments up and down the beach = stable and straight beach
what are drift-aligned beaches?
waves approach at an angle and sediment is moved along by longshore drift = wide beaches but uneven in sediment
what are examples of sources of sediment?
- rivers
- constructive waves (from seabed)
- cliffs
- LSD