Physical landscapes in the UK - Coasts Flashcards
what causes a wave
waves are caused by the transfer of energy from the wind to the sea due to friction of the water’s surface
features of constructive waves
low wave frequency
strong swash
low energy
weak backwash
forms a wide, sloping beach
low wave frequency (8-10 waves per minute)
low wave height (<1m)
build up beaches
features of destructive waves
high wave frequency (10-14 per minute)
high energy
weak swash
strong backwash
forms a steep, narrow beach
tall wave height (>1m)
short wave length
erodes beaches
what is a fetch
the stretch of ocean water over which the wind blows
what affects a wave
wind strength
how long the wind blows for
length of fetch
how do waves form
circular movement of water particles
friction between sea bed and water slows down base
water particles move in oval shape
top of wave moves faster as there’s more friction which causes the bottom to slow down
wave breaks as the top becomes unstable
water rushes up beach at an angle - swash
water rolls back to sea at right angle - backwash
define wavelength
horizontal distance between two crests
define crest
top of a wave
define trough
base of a wave
define wave height
vertical distance between trough and crest
define wave frequency
number of waves breaking per minute
what is weathering
weathering is the break down of rocks by the action of the weather and happens in one place (situ) which can weaken a coastline so it is prone to erosion
what are the two types of weathering
mechanical and chemical
what is mechanical weathering
mechanical weathering is when rocks get disintegrated and it usually associated with extremes of temperature an results in piles of angular rock fragments (scree) at the bottom of cliffs
what are the types of mechanical weathering
freeze thaw
salt
what is the process of freeze-thaw weathering
water gets into cracks in the cliff face
water freezes where temperature fluctuate repeatedly above and below freezing
the crack is opened up and widened as the water freezes and expands
stresses are created in the rock and over time the crack widens and the rock falls to pieces
what is the process of salt weathering
seawater contains salt which can weather rocks as the waves crash onto the cliff
when the seawater evaporates from the cliff, it leaves behind salt crystals
if the crystals get into cracks or holes, they can grow and expand
this puts pressure on the rock and flakes may eventually break off
whats is chemical weathering
weathering that happens when there is a chemical reaction causing the rock to decompose or break up
what is chemical weathering also called
carbonation
what is the process of carbonation
rainwater mixes with carbon dioxide in the air
rainwater becomes a weak carbonic acid
the acid attacks alkaline rocks e.g chalk and limestone
the rock is slowly dissolved by the acid rain and weakens over time
what is mass movement
when rocks loosened by weathering move down a slope / cliff under the influence of gravity
what are the types of mass movement
slides (mud and rock)
slopes
falls
what is a slide
when large chunks of rock fall down quickly without any warning
features of a slide
happens along a straight slip plane where the rock falls and maintains contact with the cliff
usually wet, rapid and tend to occur where slopes are steep (>10 degrees)
the leading edge of the slide collects as a pile of rocks on the beach or in the sea
happens in areas weakened by weathering and often after heavy periods of rainfall which has infiltrated the cliff
soil spreads out and makes a lobe at the base of the slide
mud - wet, rapid and steep
rock - rock sliding down straight slip plane and maintaining contact
what is slumping
when rock in the cliff slowly slips down into the sea as the soft rock fills with water - often happens in cliffs with slippery clay at the bottom
features of a slump
follows a concave slip plane as it rotates as it slips
permeable rock and soil due to rainfall causing it to become saturated
maintains contact with the cliff at it rotates
often caused when there is a clay layer (impermeable) under a sand layer (permeable)
what is a rock fall
when fragments of rock break away from the cliff face, often due to freeze-thaw weathering
features of a rock fall
the rocks fan out at the base of the slope to form a scree slope
bare, well-jointed rocks are particularly prone to freeze-thaw weathering which causes the rock to disintegrate
individual pieces of rock fall from the steep cliff and loose contact with it
what types of mass movement could have happened at Holbeck Hall
sliding or slumping
how could have sliding occurred at Holbeck Hall
as there is a lobe at the bottom of the slope which is common with slides
it happened overnight which means that it must have been quick which slides are (particularly mud)
there are steep cliffs in that area and there are also rock around the lobe
how could have slumping occurred at Holbeck Hall
sections of land and grass fell down
since it is in a coastal location, it is likely that there were clay layers which are slippery - causing it to slump down
what is decomposition (waves)
where waves drop and leave behind the material they were transporting (sediment) which results in more sediment staying on the beach which is then taken away by the backwash
why does decomposition (waves) happen
coastal decomposition takes place in areas where the flow of water slows down which means that the waves loose energy and are no longer able to transport material
where does decomposition (waves) happen
waves loose energy in sheltered bays and where water is protected by headlands, spits of bars (coastal landforms) and sediment can no longer be carried or moved and is therefore deposited. this explains why beaches are found in bays, where the energy of the waves is reduced and why mudflats and saltmarshes are often found in sheltered estuaries behind spits where there is little flow of water
what is wave refraction and why does it happen
wave refraction is when waves approach the shore at an angle and this makes the wave change direction or refract and this is because the part of the wave nearest the shore will be moving slower than the part further away
what is a prevailing wind
the strongest wind
describe the process of longshore drift
sediment is transported in the direction of the prevailing wind by the swash of the wave which travels at an angle to the shore and then the backwash running back down the beach at a right angle. this moves the sediment along the beach, with less sediment transported each time until the sediment hits a block e.g groyne
what are the two types of coastline
concordant
discordant
what is a concordant coastline
where different layers of rock (hard and soft) run parallel to the coastline e.g Lulworth Cove in Dorset
what is a discordant coastline
different layers of rock (hard and soft) run at right angles to the coastline and the soft rock will be eroded faster than the hard rock causing headlands and bays to form
what is folding
where many sedimentary rocks that formed on the seabed were raised to the surface by mountain building tectonic processes and these were so powerful that they folded the rocks so they’re layers (strata) are not longer horizontal which creates lines of weakness which can be easily eroded
what is a fault line
when tectonic forces caused the rocks to fold, they sometimes snapped the strata rather than bending them which means that movement can now occur as the rock layers are no longer joined and a fault is formed which creates lines of weakness which can be easily eroded
what is a landform
a feature of the landscape which is formed by the processes of erosion, transportation and deposition
how does geology and rock type influence coastal landforms
some rocks are tougher and more resistant to erosion such as limestone, chalk and granite
some rocks are softer and are less resistant to erosion such as clay and sand
what is differential erosion
when some rocks get eroded faster than others
describe how headlands and bays are formed
they are formed when soft rock on discordant coastlines is eroded quicker than the hard rock - as it is less resistant - which causes differential erosion . the soft rock gets eroded due to hydraulic action faster than the soft rock and causes bays to form which causes the hard rock to ‘stick out’ and form the headlands
how do wave cut platforms form
cliffs are made of bands of hard and soft rock
hydraulic action and abrasion erodes the soft rock between the high and low tide mark - creating a wave notch and an overhang
as this process continues, the overhang gets larger as it gets undercut
the overhand then collapses and leaves behind deposit - allowing further erosion through attrition
this process repeats again which creates another overhang
this whole process repeating, causes the cliff to retreat until the tide doesn’t reach it, or it hits a solid band of hard rock
how does an arch form
when a wave breaks through a headland
what are beaches made from
sand or shingle
how are beaches formed
beaches are formed by constructive waves as they have a strong swash and weak backwash so they deposit more material than they erode as they loose energy when the waves go back out to sea as it is mostly all used up in the swash
where are beaches found
beaches are found between the high and low tide mark - usually in sheltered areas as the sea has less energy there which causes deposition to occur and build up the land
features of a sandy beach
shallow and flat gradient
constructive waves
long stretch inland
has sand dunes
small water filled depressions (runnels) form during low tide
features of a pebble beach
steep
destructive waves
short stretch inland
large pebbles
pebbles increase in size the further back you get
what is a beach profile
shows the gradient from the back of a beach to the sea
what is the foreshore
the intertidal zone repeatedly covered, then uncovered by changing tides
what is the berm
a terrace on the beach that has formed in the backshore and is formed by constructive waves transporting material onto the beach
what is the nearshore
the breaker zone where the waves break
what is the offshore
fairly far out to sea where the waves do not break
what is the backshore
an area that is not usually affected by waves, so the sand is usually dry
how are berms formed
berms are formed in calm weather when constructive waves transport material onto the beach
while an existing berm is moved up the beach by storms and spring tides, a new berm may develop and change the beach profile
how does the berm / beach differ throughout the year
in winter, berms and sometimes the sand dunes at the back of the beach, are eroded by destructive waves which drag beach deposits offshore to create an offshore bar
this lowers the height of the beach
in late spring and summer, so long as longshore drift is not depleting the beach of sand, constructive waves will rebuild the beach
the offshore bar is worked by the waves to rebuild the berms, and dunes are replenished by saltation by the wind
destructive waves often result in winter profiles that are narrower and steeper
what is hard engineering
hard engineering is about building physical structures which try to control natural coastal processes
what are the types of hard engineering
sea walls
gabions
groynes
rock armour
how does a sea wall work
a concrete or rock barrier made against the sea, placed at the foot of cliffs or at the top of the beach
they may have a straight edge to form a barrier to a curved edge to reflect the waves back into the sea
how much does a sea wall cost
£5,000-£10,000 per metre
advantages of a sea wall
TBC
disadvantages of a sea wall
can look obtrusive and unnatural
very expensive and high maintenance costs
how does rock armour work
piles of large boulders are dumped at the foot of a cliff
the rocks force waves to break, absorbing their energy and protecting cliffs
brought by barge to coast
how much does rock armour cost
£200,000 per 100m
advantages of rock armour
relatively cheap and easy to maintain
often used for fishing
can provide interest to the coast
disadvantages of rock armour
rocks are usually from other parts of the coastline or abroad
these location can be areas protected due to their unique scenery
can be expensive to transport
doesn’t fit in with the local geology
can be obtrusive
how does a gabion work
wire cages filled with rocks that can be built up to support a cliff or provide a buffer against the sea
the rocks absorb the energy from the sea
how much do gabions cost
£50,000 per 100m
advantages of gabions
cheap to produce and flexible
can improve drainage
will become vegetated and blend in
disadvantages of gabions
look unattractive
cages last 5-10 years before they rust
how do groynes work
timber or rock structures built out to sea from the coast at right angles
they trap sediment being moved by longshore drift and enlarge the beach
the wider beach acts as a buffer to reduce wave damage
how much do groynes cost
timber: £150,000 per 200m
advantages of groynes
creates a wider beach which increases popularity
useful for fishing
not too expensive
disadvantages of groynes
they starve beaches further along the coast as they interrupt longshore drift leading to increased rates of erosion elsewhere
problem is shifted rather than solved
they are unnatural and can be unattractive
what is soft engineering
soft engineering tries to work with natural compounds without using artificial structures and it is a sustainable approach to managing the coast
what are the types of soft engineering
managed retreat
dune regeneration
beach nourishment
reprofiling
what is beach nourishment
replacement of lost sediment
a nourished beach means fewer waves reach the back
as wave energy is absorbed by the beach, rate of erosion is reduced
includes ‘beach recharge’ where sediment is taken from a bay and placed on a beach that’s loosing sand and ‘beach recycling’ where sediment is moved back along a coastline to where it started
cost of beach nourishment
£500,000 per 100m
advantages of beach nourishment
natural and blends in with the environment
attracts tourists
beach becomes wider and protects against erosion more effectively
disadvantages of beach nourishment
needs constant maintenance
bulldozers disrupt access to the beach
can be damaged by storms
what is reprofiling
artificial reshaping of the beach using existing material
after storms, bulldozers move shingle up
like beach nourishment, it ensures that the beach is large enough to be an effective buffer between the land and sea
it also creates a steeper slope which the waves have to travel - this reduces their energy and power
cost of reprofiling
TBC
disadvantages of reprofiling
constant maintenance needed
bulldozers disrupts access to beach
the shape of the beach can be difficult for tourists and other beach users
can be damaged by storms
advantages of reprofiling
natural and blends in with the environment
residents and business owners feel safe
prevents large waves reaching the back of the beach
what is dune regeneration
artificial creation of new sand dunes or the restoration of existing ones
marram grass is planted to stabilise the dunes and fences are used to keep either people off areas or encourage new dunes to develop
dunes act as a natural barrier to the destructive power of the sea
advantages of dune regeneration
natural and blends in with the environment
establishes a wildlife / wetland area
creates new habitats
cost of dune regeneration
marram grass - £200 - £2000 per 100m
new dunes - £400 - £2000 per 100m
disadvantages of dune regeneration
can restrict access and alter the view
people often ignore the signs and fences to access the dunes for recreation
what is managed retreat
deliberate policy of allowing the sea to flood or erode an area of land that is low in value
it allows natural processes to take place in a managed way e.g people are moved out, farmers are compensated and buildings are demolished
sometimes an existing sea wall may be removed to allow the area behind it to flood - but only if a new inland area of defence or embankment is then built, allowing the area between it to flood naturally
cost of managed retreat
TBC
advantages of managed retreat
reduces flooding along the coastline
natural and blends in with the environment
establishes a wildlife / wetland area
residents and building owners along the coast feel safe
lower cost maintenance
disadvantages of managed retreat
compensation needed
some land owners loose their land
can be damaged by storms
time consuming and initially costly
