Coasts Flashcards
Swash
The movement of a wave up a beach
Backwash
The movement of a wave down a beach to the sea.
Concordant coastline
-same type of rock all along the coastline
Discordant coastline
-hard soft rock arranged in layers at 90 degree angles to the coast
Fetch
-the distance the wave has travelled
What is a spit?
-a ridge of sand connected to the coast at one end where the coast changes direction due to longshore drift
What determines the size of a wave?
Fetch
Wind strength
Wind duration
Destructive
- formed from strong winds
- waves have long fetch
- tall and steep
- closely spaced (11-15 wave breaks every minute)
- stronger backwash than swash
- very powerful so causes coastal erosion- beach removal
Constructive wave
- formed from weak/light wind
- shorter fetch
- low in height
- widely spaced (6-9 wave breaks per minute)
- stronger swash than backwash
- beach building due to deposition
Formation of headlands and bays
- headlands and bays form on discordant coastlines
- hard rock e.g. granite erodes more slowly forming a headland e.g. Peveril Point
- soft rock such as sandstone erodes more quickly, forming a bay e.g. swanage bay
- abrasion and hydraulic action most significant here
- beach forms in the bay due to wave refraction
Formations of a wave-cut platform
- the sea attacks the headland at high tide
- hydraulic action and abrasion cause a wave-cut notch to form at the base of the cliff/headland
- overtime, the wave0cut notch grows in size becoming bigger and bigger
- the overhang above the notch collapses as it lacks support
- the process repeats causing the cliff to retreat inland
- this causes the wave cut platform to grow in site
- the wave cut platform is visible at low tide
- rock pools can form at wave-cut platforms
Formation of a stack
- the crack forms along weaknesses in the rock due to erosion
- the crack widens due to hydraulic action and abrasion forming a cave
- the cave grows in size and is eroded through the headland forming an arch
- the roof of the arch collapses due to lack of support forming a stack
- the stack erodes down - weathering also breaks down the stack- forming a stumo
- real life examples are Old Harry, Dorset
Longshore drift
- the swash moves the pebble up the beach in a north-east direction due to the direction of the prevailing wind whihc comes from the south-west
- the backwash takes the pebble straight down the beach in a southerly direction 90 degree angles to the coast due to the force of gravity
- the whole process repeats causing the pebble to move from west to east in a zig zag formation.
Formation of a spit
- longshore drift moves material along the coast from west to east
- when the coastline changes direction, longshore drift continues, forming a spit
- a hook forms on the end of the spit if direction of the prevailing wind changes
- the water behind the spit is sheltered so deposition occurs forming a salt marsh
- the fast river flow stops the spit extending across the river mouth
Where does a spit form?
-where the coastline changes direction
Beaches
- forms from eroded material
- formed from constructive waves
- forms in bays due to wave refraction
Formation of bars
- longshore drift moves material along the coast from the west to east in a zigzag formation
- the swash moves up the beach at an angle due to the direction of the prevailing wind
- the backwash moves straight down the beach due to the force of gravity
- longshore drift continues forming a ridge of sand and shingle (mix of sand and stones) across the bay
- a lagoon forms behind the bar
What is beach nourishment?
- sand is added to the beach to make it wider and larger
- soft engineering
advantages of beach nourishment
- creates a large beach which will ancourage tourism
- the beach will absorb the wave’s energy, reducing the rate of erosion
- cheaper, £2000/m
disadvantanges of beach nourishment
- needs constant maintenance thus can be expensive over time
- the work required can disturb beach users
what is offshore reef
- old tyres or ships are sunk in front of the coast
- soft engineering
advantages of offshore reef
- creates new marine habitats for animals and plants
- the reef absorbs the wave’s energy reducing the rate of erosion
- cheaper £5000/m
disadvantages of offshore reef
-reef can disturb fishing
What is a seawall?
- where concrete is placed at the base of the cliff or at the top of a beach
- hard engineering
Advantages of seawalls
- the wall rebounds the wave’s energy, reducing the rate of erosion
- walkways and promenades are built on top of the seawalls attracting visitors
disadvantages of seawalls
- expensive - £5000-10,000/m
- unattractive and unnatural
- leads to the erosion of the beach in front of the sea wall
what is a groyne
- rock/wood structures are placed at 90 degree angles to the coast
- hard engineering
advantages of groynes
- the groynes trap sediment making the beach larger, which attracts more tourists
- the larger absorbs the wave’s energy reducing the rate of erosion
disadvantages of groynes
- increase the rate of erosion down the coast
- unnatural
- fairly expensive because you need to build a number of groynes £5000/m
what are ripraps
- large boulders are placed at the base of the cliff
- hard engineering
advantages of rip rap
- rocks absorb the wave’s energy reducing the rate of erosion
- relatively quick to place rocks along the coast
coastal erosion
The breaking down and removal of material along the coast.
Coastal retreat?
-when coastal erosion causes the coastline to move further inland
effects of coastal retreat and flooding
- wildlife habitats destroyed
- cliffs become dangerous for walkers
- distruption to communication networks-roads and railway lines creating difficulties for commuters
- loss of people’s homes
- increased deposition further along the coast
- loss of businesses (caravan parks, cafes etc)
- decreasing value of porperties in difficulties in obtaining home insurance
