coastal systems - systems and processes Flashcards
what factors does wave energy depend on
speed of the wind - the faster the wind is travelling the bigger the wave will be
time of wind - the wave will get larger the longer the length of time the wind is hitting it
distance of wind - the farther the wind travels against the wave (fetch) the bigger the wave will be
what are the parts of a wave
wavelength
wave height
trough
still water level
crest
what is the wave height of a wave
height difference between a wave crest and neighboring trough
what is the wavelength of a wave
distance between successive crests
what is the wave frequency of a wave
time for one wave to travel the distance of one wavelength or the time between one crest and the following crest passing a fixed point
how do waves work
wave motion confined to a depth of one wavelength
waves follow a circular orbit but don’t change position greatly - it is the energy which creates the wave that moves - knows as oscillatory waves
the shallowing of water and relative rising of the sea floor affects the orbital movement of the wave
this leads to an increasing of wave height and shortening of wavelength as the coast nears
the upper portion of the wave will then spill over leading to the swash of the wave up the coastline
wave moves up and backwards, moves up and forwards, moves down and forwards, moves down and backwards
how do waves breaks
as air moves over the water frictional drag disturbs the surface and forms ripples of wave
in the open water waves have a circular orbit
as the waves approach the coast the sea bed gets higher
friction between the sea bed and the bottom of the wave causes the orbit to become elliptical
the wave will eventually break and the swash moves up the water and backwash returns to the sea
what are the characteristics of a constructive wave
low wave with long wave length - up to 100m
break gently with a low frequency of around 6-8 waves per minute
have a strong swash which carries material up the beach and a weak backwash which doesn’t take the material away
material moved up the beach leading to the formation of ridges
allows material to be deposited along the coastline and for features such as spits, tombolos and bars
long waves so roll onto the beach instead of crashing onto it
create a wider, gently sloping beach
sometimes do not seem to break but just run up the beach loosing energy as they do so
more material pulled up the beach than dragged back down
increase in beach sediment if there are not many waves each wave will be bale to complete both its swash and backwash without interference from the next wave coming up the beach
what are the characteristics of destructive waves
high in proportion to their length
high frequency breaking at an avergae rate of 10-14 waves/min
as approach beach they rapidly steepen and when breaking they plunge down
backwash much stronger than swash, sediment carried back to sea
erode the coastline, associated with steeper beach profiles
form features such as wave cut platforms, headlands, bays, arches, stacks, stumps and caves
tall waves meaning they have a greater distance to fall when they break causes them to scour out the beach material
what is a negative feedback loop of waves
constructive wave deposit material on the beach
over time the beach steepens so work against the constructive wave
waves then become more destructive
material removed from beach and deposited offshore
the beach is less steep so encouraging constructive waves
what is wave refraction
waves do not come straight into the shore - usually arrive at an angle
angles approach of a wave towards the shore can change the direction of wave travel
one end of wave feels bottom and slows down while the rest of the wave continues at its deep water speed
as more and more of the wave comes into contact with the sea floor more of it slows down
as the wave slows progressively along its length, the wave crest changes direction and becomes parallel to the shoreline
how does wave refraction occur on irregular coastlines
each wave nears coast it drags in the shallow water
causes the wave to become higher and steeper with a shorter wavelength
part of the wave in deeper water moves forward faster causing the wave to bend
overall affect is that wave energy become concentrates on the headland causing greater erosion which leads to the development of features such as cliffs caves and arches
where the waves diverge they lose power and drop their sediment forming beaches
how does wave refraction occur on headland and bays
waves approach a bay, they diverge and there is a reduction in energy, resulting in deposition.
at a headland the waves refract (bend around) the headland and the orthogonals (wave direction) converge resulting in the concentration of energy on the headland and its subsequent erosion.
Longshore currents caused by the breaking of waves on the headland will result in movement of the material eroded from the headland into the bays, thus strengthening the beaches.
what is physical weathering
the break up of rocks without any chemical changes taking place
what is chemical weathering
chemical reaction where salts may be dissolved or a clay like deposit may result which is easily eroded
what is biological weathering
breakdown of rocks by organic activity
which wreathing processes are physical
wetting and drying
crystallisation
exfoliation
freeze thaw
what is wetting and drying
rock alternates between being wet and dry. Some rocks such as shale expand when they are wet and contract when they are dry causing cracks to form in the rocks.
what is crysillisation
the high salt content of sea water can lead to the growth of salt crystals within the rock that exert pressure on joints and lead to fracturing.
what is exfoliation
rock may expand as it is heated by the sun and contracts when it cools. This can cause cracks to form in the rock.
what weathering processes are chemical
oxidation
carbonation
what is oxidation
rocks containing iron compounds experience oxidation (rusting) when exposed to oxygen and water from the air and the sea. This causes disintegration.
what is carbonation
coastlines composed of chalk or limestone are dissolved by acidic rain and seawater
what weathering processes are biological
plants
animals
how can plants be weathering processes
The roots of plants on cliff tops can create and expand tiny fissures. Sub surface seaweed can also attach to rocks and weaken them during movement.
how can animals be weathering processes
Surface animals such as puffins may excavate nesting burrows in cliffs. Sub surface creatures such as limpets may also remove rock when they attach to it
what is erosion
the breakdown and subsequent removal and transportation of material
usually caused by the direct action of the sea on the shore
what are erosional processes
hydraulic action
abrasion
quarrying
solution
corrasion
attrition
what is hydraulic action
force of water as it crashes against the coastline
wave advances air can be trapped and compressed either in joints in the rock or between the breaking wave and the cliff
when the wave retreats the compressed air expands
continuous process weakens joints and cracks in cliff causing pieces of rock to break off
simultaneously bubbles formed in the water may implode under the high pressure
generates tiny jets of water which will over time erode the rock
what is abrasion
sediment dragged up and down or across the shoreline eroding and smoothing rocky surfaces
important in formation of wave cut platform
what is quarrying
the action of waves breaking against unconsolidated material such as sands and gravel
waves scoop out the loose material
what is solution
weak acids in seawater can dissolve alkaline rocm or the alkaline cement that bonds rock particles together
action of this type of erosion may be indistinguishable from carbonation - a type of weathering
what is corrasion
when waves advance they pick up sand and pebbles from the seabed, a temporary sote or sediment sink
when they break at the base of the cliff the transported material is hurled at the cliff foot - chipping away at the rock
example of energy flow in action within the coastal system
the size shape and amount of sediment picked up determines the relative importance of the erosive process
what is attrition
not directly responsible for the erosion of the coastline
the gradual wearing down of rock particles by impact and abrasion, as the pieces of rock are moved by waves tides and currents
process gradually makes stones rounder and smoother
what is mass movement
Mass movement is the movement of consolidated material (solid rock) and unconsolidated material (clay and soil) due to gravity.
what are the types of mass movement
rockfall (fastest)
landslides
runoff
mudflows
slumping
soil creep (slowest)
what is rockfall
the sudden collapse or breaking away of individual rock fragments at a cliff face
most commonly associated with steep or vertical cliffs in heavily jointed and often quite resistant rock
rockfall often triggered by mechanical weathering (particularly freeze fall) or an earthquake
once broken away from the source rocks fall or bounce down the slope to form scree at the food of the slope
scree often forms a temporary store within the coastal system with material gradually being removed and transported elsewhere by the sea
when this occurs the scree forms and input into the sediment cell
what is landslides
block of rock moving very rapidly downhill along a planar surface, often a bedding plane that is roughly parallel to the ground surface
moving block of material in a landslide remains largely intact
frequently triggered by earthquakes or very heavy rainfall when the slip surface becomes lubricated and friction is reduced
landslides tend to be very rapid and pose a considerable threat to people and property
1993 - 60m of cliff slid onto the beach near scarborough in north yorkshire taking with it part of the holbeck hall hotel
what is runoff
link between the water cycle and the coastal system
when overland flow occurs down a slope or cliff face small particles are moved downslope to enter the littoral zone potentially forming an input into the sediment cell
runoff can be considered a type of flow that transfers both water and sediment from one store (the rock face) to another (a beach/sea)
what is mudflows
earth and mud flowing downhill
over unconsolidated or weak bedrock e.g. clay
after heavy rainfall
water gets trapped within the rock increasing pore water pressure which forces rock particles apart and leads to slope failure
pore water pressure - form of energy within the slope system, extremely important factor in determining slope instability
mudflows often sudden and fast flowing so can represent a significant natural hazard
what is slumping
slide surface is curved rather than flat
landslips commonly occur in weak and unconsolidated clays and sands often when permeable rock overlays impermeable rock which causes a build up of pore water pressure
slumps are formation of a scar
multiple landslides can result in a terraced appearance on the cliff face
what is soil creep
extremely slow form of movement of individual soil particles downhill
precise mechanism of movement often involves particles rising towards the round surface due to wetting or freezing and then returning vertically to the surface in response to gravity as the soil dries out or thews
zigzag movement similar to that of longshore drift
soil creep cannot be seen in operation but its action can be implied by the formation of shallow terracettes, the build up of soil on the upslope side of walls and the bending of tree trunks
what is what is the dominant transporter of beach material
the sea - waves move material up and down beaches when approaching the coast directly
longshore drift
what is longshore drift
Swash transports material up the beach; backwash removes it down the beach. Longshore drift is the movement of sediment along the coast
occurs as swash moves up the beach at the same angle as the prevailing wind and backwash scours material back to sea at right angles to the shore
material is therefore moved along the beach in a zigzag motion over a period of hours. Offshore currents such as rip currents move material out to sea at right angles to the shore. As they weaken further offshore the material is deposited to form sand banks.
what is transportation
plays major role is the coastal system
transferers sediment from one store to another
manifestation of energy flow governed, controlled and determined by the power of the waves, tides and currents
what are the four methods of transportation
traction
saltation
suspension
solution
what is traction
the rolling of coarse sediment along the sea bed that is too heavy to be picked up and carried by the sea
what is saltation
sediment bounced along the seabed light enough to be picked up or dislodged but too heavy to remain within the flow of water
what is suspension
smaller lighter sediment picked up and carries within the flow of the water
what is solution
chemicals dissolved in the water transported and precipitated elsewhere
this for om transportation plats an important role in carbon cycle transferring and redepositing carbon in the oceans
what are they key factors in affecting the type of transportation
velocity (energy)
particle size (mass)
in high energy environments large particle will be able to be transported whereas in low energy environments only the finest particles will be transported
what is deposition and when does it take place
Takes place when the velocity (energy) of the water (or wind) falls below a critical value for a particular size of particle and can no longer be transported
High energy environments e.g south coast of england - Clay and sand will be easily transported away leaving behind the larger coarser pebbles, Shingle beaches
Low energy environment e.g river estuaries in the lee of spits - Very smallest particles will eventually drop to the seabed to form mudflats, Some sediment may be carried offshore to form underwater sandbanks
Areas of deposition are all sediment stores or sinks
Some sediment sinks considered outputs they can also act as important inputs to the coastal system E.g. offshore sediment deposits have been driven onto the south coast of England by rising sea levels following the end of the last glacial period
what are the causes of deposition/a decline in energy
During process of longshore drift
Coastline changes, there is a river estuary
At a headland
The formation of constructive waves
how does the process of longshore drift cause deposition/a decline in energy
coastline changes and longshore drift continues to move material, energy will reduce and the transportation will stop, depositing material offshore as a spit.
how does a coastline change to a river estuary causes deposition/a decline in energy
flow of water from the river into the sea can further reduce the energy of the waves; hence deposition may occur
requires constant dredging to keep port routes open.
how does a headland cause deposition/a decline in energy
wave energy is intensified at the promontory due to refraction and low energy waves then splay out into the bays either side. Material is then deposited in the bays due to reduced wave energy.
how does the formation of constructive waves cause deposition/a decline in energy
Constructive waves have a low frequency, a long wavelength and a low amplitude
When they break on a beach, they have a strong swash and a weak backwash
Means they deposit more material on a beach as the strength in the swash allows the wave to travel far up the beach before deposition takes place
When they deposited material on beach, the energy in the wave is lost and much of the water percolates into the beach material and therefore the backwash is weak
Means material will be left on the beach with a net accumulation
The repeated action of pushing material up a beach eventually leads to the development of ridges, or berms on a beach
what causes tides
gravitational pull of moon and sun
moon has greater influence because it is closer
what are the tides like in the UK
generally have two high tides and two low tides each day
12h 25m between high tides
what is tidal range
the vertical difference in height of sea level between high and low tide
what is ocean current
large scale movement of water in oceans
what is storm sure
the pushing of the eater against a coastline to abnormally high levels, usually a combination of extreme low pressure and high tides
what is a spring tide
tides that occur twice a month when the moon sun and earth are in a straight line
produces highest monthly tidal range
what is a neap tide
tides that occur twice a month when the sun and moon are at right angles to the earth
gives lowest monthly tidal range
when an area experiences high tide what tide will the opposite side of the earth experience and why
will have high tide at the same time because the earth itself is drawn towards the moon away from the water
what are tides
the periodic rise and fall of the sea level
what is high tide
moon pulls water towards it
compensatory bulge on the opposite side of the earth - created by the earth itself pulling away from the water on the other side
where is low tide
the areas of the world between the two bulges
tide is at its lowest
what is the significance of tide
movement of tides can generate ocean currents that influence the direction and scale of coastal sediment movement.
When high tides are combined with a low pressure weather system an extremely high storm surge can be generated that leads to flooding along coastal areas.
Regular movement of the tides can be used to generate renewable energy e.g Swansea Bay, Wales
