3.1.3.2 Coastal Landscapes in the UK Flashcards
How are waves formed?
- waves are formed by the wind blowing over the sea
- friction with the surface of the water and the transfer of energy from the wind blowing over the surface to the sea causes ripples to form and these develop into waves
- waves can also be formed when earthquakes or volcanic eruptions shake the seabed - these waves called a tsunami
Example of a tsunami:
- in March 2011 a wall of water up to 40m high crashed into the Japanese coast north of Tokyo destroying several coastal settlements and killing over 20,000 people
Fetch:
- the distance the wind blows across the water
- the longer the fetch the more powerful the wave
Swash:
part of wave that crashes onto the shore when a wave breaks
Backwash:
part of wave sweeping back into the sea under the force of gravity after a wave break
Wave frequency:
number of waves that pass a certain point per second
Wave crest:
top of the wave
Wave trough:
bottom of the wave
Wave length:
distance between 2 successive crests on 2 waves
What affects the size of a wave?
- wind duration - how consistently and the length of time the wind blows for
- distance of sea over which the wind has blown
- strength of the wind - greater the wind the greater the frictional drag and therefore the greater the size of the wave
- wind speed
- fetch - distance the wave travels across the water
Sea waves:
waves that travel short distances and are the result of local waves
Swell:
waves that formed from distant storms and travel large distance
Which part of England has waves with an incredibly long fetch and why?
- the South West of Britain is affected by waves that have an incredibly long fetch, as the South Westerly wind (prevailing winds) which blow the sea there travel uninterrupted for thousands of miles across the Atlantic Ocean
- due to this waves are large in Cornwall and generally great for surfing
What is the fetch from Brazil to SW England?
9,000km
What would be the ideal conditions for erosion in England
- onshore SW winds with frequent gusts 160+ km/hr
- long fetch over Atlantic Ocean = storm conditions e.g. Cornwall 4-5 January 1998
Constructive waves:
able to build the beach as swash is stronger than backwash
Characteristics of constructive waves:
- low waves (but have long wavelength - up to 100m) that surge up the beach and ‘spill’ with a strong swash
- carry and deposit large amounts of sand and pebbles and ‘construct’ the beach making it more extensive due to strong swash - beach material moved upwards
- surfers prefer constructive waves because they give longer rides
- strong swash however it rapidly loses E as water percolates through beach material leaving a weaker backwash so no material is removed
- these waves are formed by storms often 100km’s away
- wave crests fare apart
- gently sloping wave front
- low frequency approx. 6-8 waves/min
- breaking wave spills forward
- associated with gentler beach profiles
Destructive waves:
destroy the beach as backwash stronger than swash so material taken back out to sea with the wave
Characteristics of destructive waves:
- formed by local storms close to coast and can ;destroy’ the beach
- waves closely spaced and often interfere with each other producing chaotic swirling mass of water
- high wave height and steep wave front (bit shorter wavelength) - become high and steep before plunging down onto beach
- little forward motion (swash) when destructive wave breaks but powerful backwash - explains removal of sand and pebbles and gradual destruction of beach
- on steep beach
- high frequency approx. 10-14 waves/min
What causes water tor rise up and break on the beach?
- water becoming shallower (friction with the sea bed) causes waves to rise upwards and break
Why when waves break on a sandy/pebbly beach the amount of backwash is often less than the amount of swash?
water soaks into a sandy/pebbly beach, so there is less backwash than swash
Why are larger pebbles found at the top of the beach with smaller pebbles found at the bottom?
- swash carries a mixture of pebble sizes up the beach and only has the energy to pull back the smaller pebbles
- over time, the sorting process results in larger pebbles being left at the top of a beach with smaller pebbles deposited at the bottom of the beach
Where did the Jurassic coast landslip take place and what happened?
- process of mass movement occurred near Seatown in West Dorset on the Jurassic coast in 2021
- such events occur frequently along this stretch of the coast where the cliffs are loose and unstable
- processes like this combine with the action of waves to shape the coastline
What happened as a result of the Jurassic Coast landslip?
the South West Coast Path was diverted away from the cliff edge to keep walkers safe
Sub-aerial:
situated, formed or occurring on or immediately adjacent to the surface of the Earth
What causes cliffs to collapse?
- cliffs collapse because of different types of weathering
- which is the weakening or decay or rocks in their original place on, or close to, the ground surface
- it is mostly caused by weather factors e.g. rainfall and changes in temperature
4 groups of processes that happen at the coast:
- weathering
- erosion
- transportation
- deposition
Weathering:
the decay/disintegration of rocks in their original place on, or close to, the ground surface (in situ)
Erosion:
coastal erosion is the removal of material and shaping (sculpting) of landforms (involves movement)
Transportation:
movement of material by the Sea
Deposition:
material that is dropped at the coast, usually due to loss of energy
3 main groups of weathering:
- mechanical
- chemical
- biological
Mechanical weathering:
- the disintegration (breaking-up) of rocks
- where this happens, piles of rock fragments called scree can be found at the foot of cliffs
Freeze-thaw weathering:
- Water collects in cracks or holes (pores) in the rock
- As temperature drops at night, this water freezes and expands
- This puts pressure on the rock at the side of the crack - makes crack in the rock bigger
- When the temperature rises and the ice thaws, water will seep deeper into the rock
- This process repeats many times
- Eventually pieces of rock break off
Salt weathering:
- sea water contains salt
- when the water evaporates it leaves behind it salt crystals
- in cracks and holes these salt crystals grow and expand
- this puts pressure on the rocks and flakes may eventually break off
Chemical weathering:
- caused by chemical change
- rainwater which is slightly acidic, very slowly dissolves certain types of rocks and minerals
Carbonation:
- rainwater absorbs CO2 from the air and becomes slightly acidic
- contact with alkaline rocks e.g. chalk and limestone produces a chemical reaction causing the rocks to slowly dissolve
Biological weathering:
- due to the actions of flora and fauna
- plant roots grow in cracks in rocks
- animals e.g. rabbits burrow into weak rocks such as sands
Mass movement:
- the downward movement or sliding of material under the influence of gravity
- once weakened by weathering mass movement can then deliver loose material to beaches and the sea to be eroded
- some mass movement processes occur slowly, such as soil creep, but some are very rapid such as rock falls
Examples of mass movement:
- Holbeck Hall, North Yorkshire
- 1993, near Scarborough
- 60m of cliff slipped onto beach
Processes of mass movement:
- rockfalls
- slumping (rotational slip)
- mud slides/mud flows
- land slides
Rockfalls:
Rockfalls are rapid though relatively rare movements and are found where slopes exceed 40°
What causes rockfalls?
- rockfalls may result from extremes of mechanical or chemical weathering and they produce debris slopes beneath the cliff as the material from the rockfall disintegrates at the cliff top
- freeze-thaw weathering shatter rocks from cliff and material will gather at the base - talus/scree slope
- It is exacerbated by the agents of marine erosion, which may increase the instability of slopes by undermining them
Slumping:
occurs where the movement appears to have a rotational element to it and may produce a curved rupture surface
What sorts of cliffs are susceptible to slumping?
- Cliffs formed on relatively weak and/ or impermeable rocks such as clays are susceptible to rotational slumping after prolonged rainfall as the raising of the water table underground reduces the internal friction of particles and facilitates failure
- Although slumped masses may have some internal cohesion, the highly saturated toe or frontal lobe of the slump may flow as it approaches the foot of the slope or cliff
Mud slides/mud flows:
usually wet, rapid and tend to occur where slopes are steep (over 10 degrees)
Example of area prone to mudflows/mud slides:
Monmouth Beach at Lyme Regis, Dorset is prone to mudflows
Where do mud flows/mud slides usually happen?
- They usually occur when vegetation cover is sparse and so cannot hold the soil in place
- They happen after a period of heavy rain
- At the base of the mudflow, the saturated soils spread out to make a lobe
(Land) Sliding:
- Cliffs formed on harder rocks, built up in layers e.g. chalk
- They are susceptible to sliding after prolonged rainfall as the raising of the water table underground reduces the internal friction of layers and facilitates failure
- The top layer becomes too saturated
- It slides over the layer beneath - rapidly moving downhill
- Slides largely retain their internal structure and move as a large mass
Main erosion processes:
- hydraulic action
- abrasion
- attrition
- solution/corrosion
Hydraulic action:
- the power of waves as they smash into a cliff which blasts and traps air into cracks, eventually causing it to break apart
- the explosive force of trapped air operating in a crack is called cavitation
- especially powerful during stormy seas
- the force of the water crumbles and removes material from cliffs
Abrasion:
- the ‘wearing away’ of cliffs or rocky platforms by rocks carried by the sea
- it refers to the ‘sandpapering’ effect as sand and pebbles are dragged over a rocky platform
- corrasion involves fragments of rock that are hurled at a cliff by the sea breaking pieces off
Attrition:
- rock fragments carried by the sea collide against one another causing to become smaller and more rounded
- material gradually becomes smaller
- not responsible for eroding platforms
Solution/Corrosion (erosion):
- when sea water dissolves certain types of rocks and minerals
- water may be slightly acidic
- in the UK, chalk and limestone cliffs are prone to this type of erosion
What determines how much erosion takes place at the coastline?
- fetch
- beach/shape of coastline
- bedding planes
- geology
Landform:
- feature of landscape that has been formed sculpted by geomorphic processes of:
- erosion
- transportation
- deposition
Factors that influence the formation of landforms:
- Rock type (lithology) - resistance of rocks (e.g. hard/tough or soft)
- Geological structure
- Enormous tectonic pressures
Rock type (lithology) - resistance of rocks (e.g. hard/tough or soft):
- some rocks are tougher and more resistant than other
- e.g. granite, limestone and chalk are more resistant to erosion than sand and clay
Geological structure:
the arrangement (juxtaposition) of rocks and features associated with folding and faulting
Folding:
crumpling of rock layers caused by extreme tectonic pressures
Faulting & faults:
- faulting is the displacement of rock along a crack
- faults are lines of weakness/cracks in rocks easily carved out by the Sea
How do enormous tectonic pressure affect coastal erosion landforms?
causes rocks to ‘snap’ rather than fold (bend) and movement/displacement
Concordant coastline:
concordant coastline has same type of rock along length running parallel to coastline
Discordant coastline:
where geology alternates between Strata (bands) of hard rock and soft rock aligned at an angle to the coastline
What coastal erosion landforms do discordant coastlines form?
- headlands
- bays
What are headlands and bays and how are they usually formed?
- common coastal landforms
- usually form when rocks of different strength are exposed
- weaker, softer rocks eroded more quickly to forms bays, under sheltered conditions, sediment is deposited to form beaches
- more resistant, harder rocks erode slower than softer rock so the more resistant sticks out into the Sea to form headlands, often battered by powerful waves to form steep cliffs
- due to lack of shelter at headlands, deposition does not occur explaining the absence of beaches
How are cliffs and wave cut platforms formed?
- The land slopes down to the Sea - freeze-thaw weathering weakens the rock
- There is marine erosion concentrated between high and low water mark. Wave pounding hydraulic action and abrasion by shingle hurled at land eroded base of cliff..
- Continued erosion over long period of time causes rock to break away and collect at base of cliff - destructive waves remove this material. Cliff now has a notch at its base. Section of cliff above notch is now unsupported and becomes more precarious as erosion continues.
- Notch enlarged and will get deeper and deeper, undercutting the cliff, to point where overhanging cliff can no longer defy gravity. Unsupported part of cliff breaks away and collapses onto the beach resulting in a steep drop called a cliff.
- As the cliff gradually retreats, the former base of the cliff is left as a wave-cut platform
- A wave cut platform is typically quite smooth due to abrasion, however, in some places it may be scarred with rock pools
How are caves, arches, stacks and stumps formed?
- Joints/faults in the rock eroded through abrasion
- Caves occur when waves force their way into cracks in the cliff face (hydraulic action). The water contains sand and other materials that grind away at the rock until the joint/fault is enlarged forming a cave (abrasion).
- If the cave is formed in a headland, erosion by the Sea waves continues on both sides of the cliff until it may eventually break through to the other side forming an arch. Sometimes top of arch is many metre above the reach of waves.
- The arch will continue to be eroded (attrition) and sub-aerial processes will cause the weathering of the top of the arch which will cause the arch to gradually become bigger
- Eventually erosion will cause the arch to become too big that il it can no longer support the top of the arch. This causes arch to collapse (due to gravity), it leaves the headland on one side and a stack (a tall column of rock no longer connected to the headland) on the other.
- The stack will be attacked at the base by coastal marine erosion processes and at the top by sub-aerial processes from all side. This weakens the structure and causes the stack to become too top-heavy causing the stack to collapse to form a stump.
Examples of arches:
- Arch called Durdle Door in Dorset
- top of arch is several metres above reach of waves
- Chalk arch, Bwa Gwyn, Anglesey
- Bwa Gywn is an arch formed by erosion in an outcrop of white quartzitic rock on the Anglesey coastline
- in the past, Bwa Gwyn was quarried for china clay
- today you can still see the grindstone used to extract the clay on top of the rocks
- can be dangerous because of unstable cliffs
Main process of transportation:
- Solution
- Suspension
- Traction
- Saltation
Solution (transportation):
dissolved chemicals often derived from limestone or chalk
Suspension:
particles carried (suspended) within the water
Traction:
large pebbles/rocks rolling along the seabed
Saltation:
a bouncing or hopping motion of particles too heavy to be suspended
Longshore drift:
- movement of sediment on a beach that depends on the direction that waves approach the coast (driven by the wind)
- where waves approach ‘head on’ sediment is simply moved up and down at the beach with little lateral movement
- if waves approach at an angle, sediment will be moved along the beach in a ‘zig-zag’ pattern called longshore drift
- the swash of the waves carries the sediment up the beach in the direction of the waves
- the backwash carries the sediment back down the beach adjacent to the coastline
- so the sediment in transported in the direction of the dominant wind (so direction of the waves)
What is longshore drift responsible for?
- responsible for number of important coastal landscapes including beaches and spits
Why may longshore drift cause problems with erosion?
longshore drift may cause problems with erosion as longshore drift transports materials from the beach - leads to lack of beach material and therefore protection for soft boulder cliffs
Why is the direction of longshore drift along the West coast different to the direction along the East coast of the UK?
as there is a change in wind direction so a change in wave direction
What is longshore drift a mixture of?
longshore drift is a mixture of geomorphic processes
Where does coastal deposition take place and what happens?
- coastal deposition takes place in areas where the flow of water slows down
- waves lose energy in sheltered bays and where water is protected by spits or bars
- here sediment can no longer be carried or moved and it is therefore deposited
- this explains why beaches are found in bays where the energy of waves is reduced - called wave refraction
Headlands and bays:
A rocky coastal promontory that is resistant to erosion
Cliff:
A steep high rock face formed by weathering and erosion along the coastline.
Wave-cut platform:
A rocky, level shelf at or around sea level representing the base of old, retreated cliffs.
Cave:
A large hole in the cliff caused by waves forcing their way into cracks in the cliff face
Arch:
a wave eroded passage through a small headland
Stack:
An isolated pillar of rock left when the top of an arch has collapsed
Waves:
Ripples in the sea caused by the transfer of energy from the wind blowing over the surface of the sea
Diagram to show movement of a wave approaching a beach:
Diagram of rockfalls:
Diagram of rotational slip/slumping:
Process of slumping:
- Waves erode the base of the cliff undercutting them creating a wave-cut notch
- Soft rock holds rainwater and run-off
- The soft rock becomes saturated at the top of the cliff and forms a slip plane
- The weight of the saturated cliff causes it to slump
- The rock slumps into the Sea
Diagram of mud flow/mud slide:
Diagram of land slides:
Diagram of coastal erosion processes:
Diagram of concordant coastline:
Diagram of discordant coastline:
Diagram of formation of headlands and bays:
Diagram of a wave cut platform:
Diagram of cave, arch, stack and stump:
Diagram to show transportation processes:
Diagram of longshore drift:
Diagram of coastal deposition:
Diagram of spit formation:
Diagram of bar:
Diagram showing how sand dunes change further inland:
Beach:
- an accumulation of eroded material transported and deposited by the Sea
- The zone of deposited material that extends from the low water line to the limit of storm waves
What can beaches be made of?
- sand
- shingle
- pebbles
How do beaches form?
- beaches form from deposited material by waves
- beach material is eroded by marine processes
- deposited material is transported by longshore drift (when waves approach at an angle to the beach but then recede directly away from it)
- waves lose energy and the become unable to continue carrying the material
- happens due to several reasons: waves may slow down as they reach an increasingly sheltered coast, sea is very shallow etc.
What sources can the material that makes up a beach come from?
- parts of the cliff face that have eroded away
- detritus and sediment from rivers
- sea bed
- longshore drift - can pull material from one beach and deposit it on another
Where are the different particles found on a beach and why?
- largest particles found at back of the beach as they can only be carried by the strongest waves - usually under storm conditions
- large ridges of shingle towards back of beaches - berms
- smallest particles found closer to where the waves break - as the breaking waves erode them into smaller, rounder particles (attrition)
- sand usually smallest component at beach - as the particles are very small, unable to build steep angles and have a gentle or shallow profile
- pebbles can pile on top of each other with more ease - so pebble beaches tend to have a steeper profile
How can a beach profile change?
- beaches not permanently gently sloping or steep
- can change throughout the year due to the different types of waves caused by different weather
- in winter, (due to storms) more pebbles may be deposited on beach making beach steeper
- in summer, due to the prevailing constructive wave, it make becomes sandier and flatter
- beaches vary size and shape twice a day with the tide
Characteristics of a sandy beach:
- Found in sheltered bays
- Strong swash
- Low energy constructive waves
- Berms (clear ridges) can mark the high tide line
Characteristics of pebble beaches:
- high-energy environments that wash away finer sand and leave behind larger pebbles - come from nearby eroded cliffs or deposited onshore from vast accumulations out to sea
Spit:
a long narrow finger of sand or shingle jutting out into the Sea from the land
How are spits formed?
- Spits are created by deposition
- Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift
- Longshore drift moves material (e.g. sand and shingle) along the coastline - this is when waves approach a beach at an angle, waves break and transport material up the beach but the backwash returns to sea at a right angle to the coast
- Material is therefore gradually transported along the beach in the direction of the dominant wind
- If there is a bay or a bend in the coastline, deposition of sand and shingle will continue to be deposited away from the coast in the open sea
- As it builds up, it starts to form an extension from the lands - continues with spit gradually growing out to Sea
- Strong winds or tidal currents can cause the end of the spit to become curved and develop into a hook (recurved hook) - if the wind changes direction further out
- Waves cannot get past a spit, which creates a sheltered area behind the spit where silt is deposited are and where mud flats and salt marshes form
- An extensive salt marsh may form as vegetation may start to grow in the emerging muddy islands
- Salt marshes are extremely important wildlife habitats and over-wintering grounds for migrations birds
Example of spits:
- Spurn head spit located on the Holderness coast in Humberside
- Spurn Head on Yorkshire Coast
Bar:
where a spit grows across a bay
How are bars formed?
- longshore drift may cause a spit to grow right across a bay trapping freshwater lake or lagoon behind it - bar
- for offshore bars out to Sea - waves approach a gently sloping coast and deposit sediment due to the friction with the seabed - build up of sediments causes waves to break at some distance before the coast
- in UK, some offshore bars have been driven onshore by rising sea levels following ice melt at end of glacial period 8000 yrs ago
- called a barrier beach
Example of a barrier beach:
Chesil Beach in Dorset, UK
Sand dune:
Sand dunes are coastal hills of sand that occur where there is enough sand exposed at low tide to dry out and be blown inland
How are sand dunes formed?
- The sand is heaped up by the wind into mounds when the blown grains hit an obstacle
- Over time, dune-building plants, which trap the sand and stabilise its movement, cover these mounds
- Even with plant cover, dunes are ever changing, dynamic habitats
- Dunes form on exposed shores, most frequently in bays
- Sand dunes develop and change over time and as they change, so too does their biodiversity
- The plants that colonise them are highly specialised to survive such dry, dynamic conditions and are not found in any other habitat - succession
Factors for sand dune formation:
- sand
- accommodation space
- weather conditions - sand only deposited velocity of wind reduces (can be caused by an object) and this causes an accumulation of sand
- wind can suspend sand
- wind may be able to make sand bounce across the beach (saltation)
- wind strong enough to move sand across surface
How are embryo dunes formed?
- Sand becomes trapped at the end of the beach
- Because the sand is so inhospitable only the very resistant plants will grow here such as lyme grass or sea couch grass - these plants are called pioneers
- As the plants grow these stabilise the dune and an embryo dune is formed
How are fore dunes formed?
- As the embryo dune develops in height and size it becomes a fore dune
- Sea couch grass is common as it is able to retain water so it can grow in arid conditions
- Marram grass is also common and this has long roots (rhizomes) to seek food/water
- This helps to stabilise the dune
Characteristics of embryo dunes and fore dunes:
- on-shore winds
- poor water retention
- transient dunes
- sand alkaline
- seaweed deposits humus
- sand builds up against pioneer plants
Characteristics of plants in embryo and fore dunes:
The plants which grow here have adaptations which allow them to grow in a difficult environment:
- waxy leaves to retain moisture and withstand winds
- prostrate (low) habit to avoid strong winds
- deep tap roots to obtain available moisture
- high salt tolerance
Examples of plants found in embryo dunes and fore dunes:
- sandwort
- saltwort
- sea rocket
- sea couch
- frosted orache
How are yellow dunes formed?
- As the dune develops further it becomes known as a yellow dune because of the sand that is found there
- The vegetation increases the amount of organic matter on the dune which is good for water retention
Characteristics of yellow dunes:
- reduces wind speeds
- ‘soil’ slightly less alkaline and more water retentive
- surface continually blown away and replenished with fresh sand
- above the level of high tides
- some humus forming
Characteristics of marram grass (in yellow dunes):
The dominant plant species is Marram grass:
- Salt tolerant
- Thrives on being buried by sand
- Inrolled leaves to reduce moisture loss
- Long tap roots
- Underground rhizomes stabilise the sand
Mobile dunes:
- embryo dune and foredunes
- yellow dunes
Fixed dunes:
- grey dunes
- dune slacks
How are grey dunes formed?
- Grey dunes are fixed dunes
- The grey like appearance is a product of organic matter and the development of humus from the vegetation
- The organic layer that develops provides good conditions for the development of vegetation such as red fescue and lichens
Characteristics of grey dunes:
- sheltered by higher, seaward dunes
- lower pH
- little mobile sand
- sand no longer accumulating
- a more closed vegetation community in which marram grass is no longer able to compete in
- higher humus content
Characteristics of plants in grey dunes:
- higher species diversity
- mainly perennials
- marram grass becomes more sparse
- surface lichens give “grey” appearance
- older grey dunes may have extensive covering of lichens and heather
How are dune slacks formed?
- In some places dune slacks develop
- These are depressions in the sand dunes which are close to the water table and are home to reeds and rushes which require lots of moisture
Characteristics of dune slacks:
- occur in low lying hollows between dune ridges
- relief intersects the water table
- soil acidic
- water table high - especially in winter
Characteristics of plants of dune slacks:
The community which develops here comprises moisture-loving plants commonly found in many fresh water wetland areas
Examples of plants in dune slacks:
- flag iris
- rushes
- phragmites reeds
- bog cotton
How are dune heaths formed?
- Behind the yellow and grey dunes the supply of beach sand is cut off
- The main plants here are heather and buckthorn
- Towards the back of the dune heath there are trees such as birch and oak
- This is beginning to become a climatic climax (the optimum vegetation for a specific climate
Characteristics of dune heaths/woodlands:
- well sheltered from winds
- acidic soil
- soil has high organic matter content
- nutrient rich
- maritime influence is minimal
Characteristics of plants in dune heaths/woodlands:
- Human interference means that true mixed woodland climax vegetation is rarely seen on dune systems in the UK
- Most dune systems develop into a community of heathland, woody perennials (often spinous) and scattered trees
Examples of plants in dune heaths/woodlands:
- heather
- sea buckthrone
