coastal systems and landscapes Flashcards
what type of system is the coast?
closed
what are sediment cells often bordered by?
prominent headlands
what is a sediment cell?
largely self contained stretch of coastline
the flows of sediment act in which ways?
dynamic equilibrium
what is dynamic equilibrium?
maintenance of a balance in a natural system, in constant state change
how does the system keep this balance of equilibrium?
inputs and outputs constantly changing to counteract any changes
how can dynamic equilibrium be affected in the long term and short term
LT- human intervention
ST- natural variations
what are the smaller areas called within each sediment cells?
sub cells
the sub cells are often used for planning what?
coastal management projects
what are feedback loops?
mechanisms which enhance changes within a system
what is positive feedback? simple
taking it away from dynamic equilibrium
what is negative feedback?simple
taking system back towards equilibrium
give an example of how a negative feedback loop would work for a storm eroding beach?
- destructive waves loose energy, deposit excess sediment as an offshore bar
- bar dissipated wave energy protect beach
- bar eroded instead of beach
- once bar has gone back to DE
give an example of how positive feedback would work for people trampling on sand dunes?
- people trample of sand dunes destroys veg increases erosion
- sand dunes completely eroded leaving beach open to erosion taking away from OG state
name 6 sediment sources
- rivers
- cliff erosion
- wind
- glaciers
- offshore
- longshore drift
what is most of sediment in the coastal zone a result of?
an input from rivers
where is the sediment sometimes deposited? then where does the sediment get transported to?
estuaries which are brackish (salty) areas where rivers flow into sea, then sediments flows through coastal systems
erosion is prominent in areas with what type of cliff?
unconsolidated (uncompacted and therefore unstable)
how is cliff erosion a sediment source?
some areas coasts can retreat up to 10m per year= sed input
how is wind a sediment source?
it transports sediment like sand (sand dunes)
how are glaciers a sediment source?
when does this occur?
glaciers flow directly into ocean depositing sediment that was stored in ice.
occurs when glaciers calve, ice breaks of glacier
how does offshore become a sediment source?
waves erode offshore sediment sink (offshore bars). sed transported to beach.
OR storm surges
how is longshore drift a sediment source?
sediment moved along beach, due to prevailing wind
what are sediment budgets?
they use data of inputs, outputs, stores and transfers to assess the gains and losses of a sediment within a sediment cell
if sediment cells are supposed to be in dynamic equilibrium why is a sediment budget needed?
because human action and natural variation can disrupt the state of equilibrium
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 waves
why is the littoral zone constantly changing?
short term and long term
short term- tides and storm surges
long term- changes in sea level and human intervention
what is the shore/shoreline?
boundary between sea and land
what is offshore?
- area beyond the influence of wave
what is onshore?
area of land not covered by the sea but close to it
what is the primary source of energy for all natural systems?
the sun
what is the main energy source at the coast?
wind or less frequently tectonic activity
how are waves formed?
-wind moves across surface of the water causing frictional drag creates small ripples, waves circular orbital motion of water particles
- shallow seabed orbit becomes elliptical
= horizontal movement of waves
-wave height ^ length/ velocity decreases
how are waves formed?
-wind moves across surface of the water causing frictional drag creates small ripples, waves circular orbital motion of water particles
- shallow seabed orbit becomes elliptical
= horizontal movement of waves
-wave height ^ length/ velocity decreases
-waves break, surges up beach
what is swash and backwash?
water up beach
water down to beach
Name three factors that affect wave energy?
- strength of wind (stronger wind=stronger waves)
- duration of wind (wind is active for longer periods of time energy waves build up and increase)
- size of fetch (distance over which wind blows, larger it is more powerful waves will be)
what do constructive waves tend to do with material? what do they create?
deposit, creates depositional landforms, increases size of beach
what do destructive waves tend to do?
remove depositional landforms through erosion, decrease size of beach.
the difference in formation in constructive and destructive waves?
con- formed by weather systems in open systems
des- stronger winds closer to coast
different in wave length for constructive and destructive waves?
con- long WL
des-short WL
Frequency of con and des waves?
6-9 per min
11-16 per min
wave characteristics of con and des waves?
low waves, surge up beach
high waves, plunge onto beach
swash characteristics of con and des waves?
strong swash/weak backwash
weak swash/strong backwash
what types of beaches do con and des waves fall on?
occurs on gently sloped beaches
occurs on steep beaches
what waves dominate in summer and what waves in winter
summer- constructive
winter- destructive
negative feedback of beaches and waves
deposition
steeper beach profile
steep beaches favour destructive waves, beach is eroded, reducing beach profile leading to constructive waves.
What is a key source of energy in coastal environments responsible for tides?
gravity
when do tides occur ?
when the gravitational pull of the sun or moon changes the water levels of the seas and oceans
what is the difference in height between the tides known as?
tidal range
when do the highest high tide and the lowest low tide occur ?
when the sun and moon are in alignment
what is another name for the lowest low tide? what type of tidal range does this create?
SPRING TIDE
largest possible tidal ranges
when do the lowest high tide and the highest low tide occur?
sun and moon are perpendicular to each other , both of the gravitational forces act against each other so overall pull is minimised
what is another name for this? what type of tide does this create?
neap tide creates smallest possible tidal range
what are rip currents? how do they form?
powerful underwater currents occurring close to the shoreline
backwash is forced under the surface forming an underwater current.
high energy coastlines are assosiated with what waves?
powerful waves (destructive), areas of large fetch
what type of landforms are assosiated with high energy coatslines?
rocky headlands and landforms
how does erosion effect these high energy coastlines?
erodes quickly as the rate of erosion exceeds the rate of depositon
what waves are associated with low energy coastlines?
less powerful waves (constructive)
what type of landforms are associated in these areas of high energy??
landforms of deposition (sandy beaches)
effect of erosion?
little as the rate of deposition exceeds rates of erosion
what is wave refraction?
the process by which waves turn and loose energy around a headland on uneven coastlines
where is the wave energy focused?
on the headlands creating erosive features in these areas
where is the energy focused?
dissipated in bays leading to formation of features associated with lower energy environments (beaches)
negative feedback of erosion
due to different rock strengths what odes erosion lead to?
the formation of headlands where resistant rock exists and bays where unconsolidated rocks and clays are dominant
what does this then increase?
the forces of erosion on the headlands and reduced erosion in the bays as wave refraction dissipates wave energy and a beach protects coast behind
what is then worn away?
headlands= increases erosion
what what would this then lead to as a result of negative feedback?
dynamic equilibrium if conditions stayed constant
name 6 types of erosion (C.A.A.H.C.W)
corrasion abrasion attrition hydraulic action corrosion wave quarrying
process of corrasion?
sand and pebbles picked up by the sea from an offshore sediment sink and hurled against cliff at high tide= erosion
process of abrasion?
sediment is moved along the shoreline, warn down overtime
process of attrition?
wave action cause rocks and pebbles to hit against each other, wearing each other down and so becoming round and smaller. has little effect on coastline itself
process of hydraulic action?
wave crash against rock or cliff face, air id forced into cracks, joints and faults within rock. high pressure= cracks force apart and widen when wave retreats air expands. bubbles in the water in rock may implode under high pressure creating tiny jets of water= erode rock
process of corrosion
mildly acidic seawater cause alkaline rock such as limestone to be eroded. similar to carbonation weathering
what is wave quarrying?
when breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m^2. similar to HA but acts with more pressure to directly pul away rocks from a cliff face or remove smaller weathered fragments. force of breaking wave hammers rock surface, weakens it leaving it open to attack from HA and abrasion.
name 4 main factors that affect coastal erosion?
- waves
- beaches
- rock type
- subaerial processes
how do waves affect coastal erosion?
erosion occurs mostly in the winter when the waves are more destructive and powerful due to frequent storms
how do beaches affect coastal erosion?
if a becah is infrount of a cliff then this will absorb most of the wave energy= reduce erosion rates. if there is coastal management being used there like groins it can increase the rate of erosion elsewhere down the beach.
how does the rock type affect the rate of erosion?
igneous rocks are made up of interlocking crystals making them more resistant to eroison
how do subaerial processes affect erosion?
weathering and mass movement like landslides weakens cliffs. rock fragments= increase in corrasion/abrasion
IGNEOUS rock
- example
- rate of erosion
- structure
-granite
-very slow (<0.1)
interlocking crystals
METAMORPHIC rock
- example
- rate of erosion
- structure
- slate
- slow (0.1-0.3 cm yr)
- crystal orientated in same direction
SEDIMENTARY rock
- example
- rate of erosion
- structure
- limestone
- very fast (0.5-10cm yr)
- lots of faults making them weak
what is coastal transportation responsible for?
transferring sediment within a sediment cell and between other sediment cells
what are the main four processes of transportation?
- traction (large heavy sediment rolls along the sea bed pushed by currents)
- Saltation (smaller sediment bounces along sea bed, pushed by currents)
- suspension (small sediment is carried within flow of water)
- solution (dissolved material is carried within the water, potentially in chemical form.)
longshore drift, how does it work?
- waves hit beach at an angle determined by direction of Prevailing wind.
- waves push sediment in this direction and up beach in swash
- due to gravity wave carries sediment back down beach in backwash
- moves sediment
when does deposition occur?
sediment becomes too heavy for the water to carry or if the wave looses energy
what are the two types of deposition?
gravity setting
flocculation
what is gravity setting?
waters velocity decreases so begins to be deposited
what is flocculation?
in salt and tidal marshes. Clay particles clump together due to chemical attraction and then sink due to high density.
what is weathering?
breakdown of rocks overs time, leading to the transfer of material into the littoral zone, becomes an input to sediment cells
positive feedback of weathering?
rate removal of the weathered rock form the base of then cliff is higher than the rate of weathering, promote further weathering as increases area of exposed rock
negative feedback of weathering?
if removal of weatherd rock from base of cliff is slower than the rate of weathering= build-up of debris at the base of the cliff, reducing the exposed cliff area= reduces rate of weathering
what is mechanical weathering?
breakdown of rocks due to exertion of physical forces without any chemical changes
name three types of mechanical weathering?
- freeze thaw
- salt crystallization
- wetting and drying
explain freeze thaw?
water enters cracks in rocks, water freezes overnight in winter. freezes water expands by 10%= cracks in rocks. weakens cliff
explain salt crystallisation?
seawater evaporates, salt left behind. salt cryst grow= exerting pressure= cracks widen. salt can corrode ferrous rock due to chem reaction
What is wetting and drying?
rock (clay)expand when wet, contract when dry. cycle= rocks/ cliffs to break up
what is chemical weathering?
breakdown of rocks through chem reactions
name 3 types of chem weathering?
carbonation
oxidation
solution
what is acrbonation?
rainwater absorbs co2= weak carbonic acid, reacts with calcium carbonate in rocks= calcium bicarbonate (easily dissolved) .acid rain reacts with limestone to form calcium bicarbonate
what is oxidation?
when minerals become exposed to air through cracks and fissures, mineral becomes oxidized= increases volume rocks crumble.
what is solution?
when rock minerals such as rock salt are dissolved
what is biological weathering?
the breakdown of rocks by organic activity
name 3/5 types of biological weathering?
- rock boring
- birds
- decaying vege
explain rock boring ?
many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face
explain how birds cause weathering?
some birds such as PUFFINS dig burrows into cliffs weakening them
explain decaying vegetation?
water that flows through decaying veg and then over coastal areas, will be acidic= chemical weathering
what is mass movement?
movement of material down a slope under the influence of gravity
Mass movement can be categorized into 4 main areas what are they?
- creeps
- flows
- slides
- falls
the type of mass movement can be dependent on what (name 4)
- cliff/slope angle
- rock type
- vegetation
- rock structure
what are the 6 types of mass movement?
- soil creep
- solifluction
- mudflows
- rock fall
- landslide
- landslip/slump
- run off
what is soil creep?
movement o soil particles down a hill.. leads to formation of shallow terraces
what is solifluction?
occurs mainly in tundra areas where land is frozen (periglacial enviro) as top layers thaw during summer the surface layers flow over the frozen layers. forms solifluction lobes.
what are mud flows?
increase in water content of soil can reduce friction, leading mud to flow over underlaying bedrock. water can get trapped in rock increasing pore water pressure= weakens slope
when does rock fall happen? what is teh cause mostly?
occurs when exposed to mechanical weathering. earthquakes, leads to scree
what is a landslide ?
heavy rainfall leads to water between joints and bedding planes in cliffs, reduce friction and lead to landslide
what is land slip?
slope is curved, water pressure leads to the land to collapse under its own weight. create a scarred appearance to the cliff face
what is run off?
water in the form of overland flow may erode the cliff face and coastal area or pick up sediment, that then enters littoral zone, transported in water via suspension
what can influence the prominence of weathering?
temperature and climate
sequence on pinnacle headland
how are small caves created?
faults in headlands eroded by hydraulic action and abrasion= small caves
how are blow holes created?
overlying rock in cave may collapse, forming blowhole.
what happens to create a wider cave?
marine erosion widens faults in the base of headland= cave
the cave will widen more and create what, due to what?
-marine erosion and sub-aerial processes, creating an arch
the arch continues to widen and what is created and how?
arch widens and is unable to support itself, falling under its own weight through mass movement= stack
what happens to the stack sue to marine erosion?
becomes a stump
what is finally left?
a wave-cut platform
where are steep cliffs most commonly found?
where rock is strong and fairly resistant to erosion
what rock is most resistant to erosion
sedimentary rocks that have vertical strata, create steep cliffs
where are gentle cliffs found?
areas with weaker rocks, less resisitant to erison
rate of retreat is dependant on what?
marine factors (fetch, beach, wave and energy) and terrestial factors (subariel processes, geology and rock strengths)
what type of cliffs are most likely to retreat?
those made of unconsolidated rock
wave cut notch and platform? sequence?
when cliffs erode concentrated around high tide line.
process of hydraulic action and corrasion create a wave cute notch
notch= deeper cliff becomes unstable falls under weight
leaves behind a platform of unaffected cliff beneath a wave-cut notch
negative feedback of a wave-cut notch?
length of wave cut platform is limited as waves cannot reach cliff reducing erosion. act of erosion creating the wave-cut platform has acted to directly decrease the rate of erosion in future
what type of landform is a beach?
depositional
when are beaches created?
when sediment is deposited near the coastline when waves loose their energy.
when does beach accretion occur?
when the beach is being built up by constructive waves (summer)
when does beach excavation occur?
in winter when destructive waves remove sediment from the beach
the effectiveness of transportation is dependant on what? and leads to different beaches.
angle of prevailing wind
what are swash aligned beaches
?
-wave approaches perpendicular to coast so there’s limited longshore drift, wave refraction reduces speed of high energy waves= shingle beach
what are drift aligned beaches?
waves approach at a significant angle, longshore drift= sediment long down beach= spit. generally larger sediment at start of beach and weathered sediment moves further down beach.
what are berms?
ridges where the high tide line is at different times of the year
what are cusps?
small curved dips in the beach where swash comes in
what are Runnells?
smaller ridges often found in smooth wet sand, caused by tides
what is a spit?
long narrow strip of land which is formed when longshore drift causes beach to extend out to sea.
what is a spit usually due to?
change in direction of the coastline
what can sediment projection create?
salt marsh due to the sheltered, saline enviro, allowing deposition of finer sediments
what does the length of the spit depend on ?
changing currents or rivers, which will prevent sediment from being deposited
can a spit extend across an estuary?
NO
what is a compound spit?
spit with multiple recurved tips
what is a double spit? what can it lead to?
were spits from opposite sides of a bay reach out towards each other, barrier beach
what is a barrier beach?
when a beach or spit extends across a bay to join two headlands this traps water behind it leading to formation of a lagoon.
what else has caused a barrier beach to form?
rising sea levels after the last glacial period.
what are barrier beaches known as when they become detached from the mainland?
barrier island
what area are they most common in?
low tidal ranges
what are tombolo’s?
a bar or beach that connects the mainland to an offshore island
what are tombolo’s formed due to?
formed due to wave refraction off the coastal island wave velocity, leading to deposition of sediment
what are offshore bars?
an offshore region where sand is deposited, as waves don’t have enough energy to carry sediment to shore
when are they formed?
when waves break early, instantly depositing its sediment as a loose-sediment offshore bar.
waves may pick up sediment from an offshore bar which then provides wha?
sediment input in to the coastal zone
how else can offshore bars be formed?
result of backwash from destructive waves removing sediment from a beach
what is a vegetation succession?
a plant community that changes over time.
on coasts where there are is a supply of sediment and deposition occurs what plants grow?
pioneer plants
what is the first stage of sand dune succession?
embryo dunes are first colonized by pioneer plants, which die and release nutrients into the sand, increasing amount of veg able to grow
stage two (enviro conditions)?
embryo dunes and pioneer plants alter enviro conditions from harsh to salty, to an eviro in which other plants can survive
stage 3 (new species)?
new species of plants can now colonise the area, change enviro progressively
why is marram grass a very good example of a pioneer plant?
- tough/flexible
- adapted to reduce water loss through transpiration
- roots 3m deep tolerate 60c temp
what are the 5 stages of salt marsh succession?
1- algal stage 2- pioneer stage 3- establishment stage 4- stabilization 5- climax vege
what happens in the algal stage?
gut weed and blue green algae establish as they can grow on bare mud, roots bind together
what happens in the pioneer stage?
cord grass grow, roots begin to stabilise the mud allowing the estuarine to grow
what happens in the establishment stage?
salt marsh grass grow , creating a carpet of vegetation and height increases
what happens in stabilisation?
sea thrift, grow and so slat rarely ever gets submerged beneath the marsh
what happens in climax vegetation stage?
rush, sedge and red fescue grass grow since the salt marsh is only submerged once or twice a year
how does vegetation help stabilise coastal sediment?
- roots bind soil=reduce erosion
- when submerged, plants provide a protective layer for ground
- plants reduce wind speed at surface
when do sand dunes occur?
prevailing winds blow sediment to the back of the beach
what does the formation of dunes require?
large quantities of sand and a large tidal range
what types of wind is also required?
frequent and strong
the dunes develop as a process of a vegetation succession.
-what helps bind dunes together
-sea rocket are resistant and able to survive in salty sand, with roots helping bind dunes together
-what allows marram grass to grow?
decaying organic matter adds nutrients and humus
larger plants colonise area, what occurs when the trees are able to colonise the area?
climatic climax
name 5 different types of dunes?
- embryo dunes
- yellow dunes
- grey dunes
- dune slack
- heath and woodland
what are embryo dunes?
upper beach area where sand starts to accumulate around a small obstacle?
what are yellow dunes?
as sand accumulates and the dunes grow, vegetation may develop on the upper and back dune surfaces, stabilises dune. tallest of dune succession
what are grey dunes?
sand develops into soil with lots of nutrients, veg dies enabling more varied plant growth
what is dune slack?
water table rises closer to surface, or water is trapped between hollows between dunes during storms, allowing development of moisture loving plants
what is heath and woodland?
sandy soils develop as there is a greater nutrients content, allowing less brackish plant to thrive. tree will also grow with coastal woodland becoming a natural windbreak to the mainland behind
why does deposition occur in river estuaries?
when the flow of water from the river meets with the incoming tides= water flow virtually cease, water can no longer carry sediment suspension
as most of the sediment is small what does this lead to a build up of?
mud, builds up till it’s above see level
deposition occurs as a result of what in salt marshes?
flocculation
why is a meadow formed
sections of the salt marsh rise above the high tide level leading to the climatic climax of the vegetation succession when trees begin to colonise the area
depositional landforms consist of what making them vulnerable to change?
unconsolidated sediment
what happens during major storms?
large amounts of sediment can be eroded or transported elsewhere removing any landform from one region of the sediment cell
what do depositional landforms rely on to balance erosion?
continuous supply of sediment, which may see some landforms changed as their dynamic equilibrium shifts
