coasts Flashcards
what type of wave has a weak swash but strong backwash?
destructive wave
what does a strong backwash do?
remove sediment from the beach
in what type of wave are the waves steep and close together?
destructive wave
what type of wave has a strong swash but weak backwash?
constructive wave
what does the swash do to the beach in a constructive wave?
brings sediment up the beach
what type of wave has low and far apart waves?
constructive wave
what is the swash?
water that rushes up the beach
what is the backwash?
water that flows back to the sea
what is the fetch of a wave?
how far the wave has travelled
what 3 things does the size and energy of a wave depend on?
the fetch, the strength of the wind, how long wind has been blowing for
what does the rock have to be in order for freeze-thaw weathering to occur?
porous or permeable
explain the steps of freeze-thaw weathering
- water enters cracks in rock
- temps drop and water freezes and expands causing crack to widen
- ice melts and goes deeper into cracks in rock
- process repeats until rock splits entirely
explain the steps of biological weathering
- plant roots can get into small cracks in rock
- they grow and cracks get larger
- small pieces of rock breakaway
explain chemical weathering
rain + seawater can be a weak acid. overtime rocks can become dissolved by the acid in the water
what 2 types of rock are prone to chemical weathering?
limestone and chalk
what is mass movement?
the downhill movement of sediment that moves because of gravity
what is rockfall?
when bits of rock fall off the cliff face usually due to freeze thaw weathering
what is mudflow?
when saturated soil flows down a slope
what is landslide?
when large blocks of rock slide downhill
what is rotational slip?
when saturated soil slumps down a curved surface
what type of wave is responsible for erosion on the coastline?
destructive
what is hydraulic action?
the sheer power of the waves, air becomes trapped in cracks in rock and causes it to breakaway
what is abrasion?
when pebbles grind along a rock platform like sandpaper causing it to become smooth overtime
what is attrition?
when rocks carried by the sea knock against each other and break apart to become smaller and more rounded
what is solution?
when sea water dissolves certain types of rock
what 2 types of rock are prone to solution?
limestone and chalk
what is transportation?
the movement of beach material
what is suspension?
when small particles eg clays or silts are suspended in the flow of water
what is saltation?
when small pieces of shingle or large sand grains bounce along the sea bed
what is traction?
when pebbles and larger material are rolled along the sea bed
what is longshore drift?
when waves approach coastline at an angle due to the direction of prevailing wind. the swash carries material up the beach and backwash flows back to sea, in a zigzag pattern
what is deposition?
when the sea loses energy and drops material it’s been carrying
what kind of coastline does deposition occur at?
coastline with constructive waves
what 4 factors lead to deposition?
waves slowing down and losing energy, shallow water, sheltered areas eg bays, little or no wind
why do headlands and bays form?
because cliffs along the coastline don’t erode at the same pace
what is a bay?
an inlet of the sea where land curves inward
how do bays form?
bands of sock rock like clay/sand are weaker so erode more quickly forming a bay
why do headlands form?
hard rock eg chalk/limestone is more resistant to erosion
how do headlands form?
when soft rock is eroded inwards, hard bands of rock stick out to sea forming a headland
how is a cave formed?
cracks widen in the headland due to erosional processes eg hydraulic action and abrasion, the rock begins to open up forming a cave
how are arches formed?
caves become larger and eventually breaks through the headland to form an arch
how are stacks formed?
the base of arch continually gets wider through further erosion until the roof gets too heavy and collapses into the sea, leaving a stack
how are stumps formed?
stack gets undercut at the base until it collapses leaving a stump
what are beaches made up of?
made up of eroded material that has been transported elsewhere and then deposited by the sea
where do beaches usually form?
bays
where are sandy beaches usually formed and why?
in bays because the waves have less energy
where are pebble beaches usually formed?
where cliffs are being eroded
what is a spit?
an extended stretch of sand/shingle jutting out to sea from the land
how do spits form?
- sediment is carried by longshore drift
- when there is a change in the coastline, deposition occurs and a long thin ridge of material is deposited which is the spit
- if the wind changes direction, a hooked end can form
- waves can’t get past a spit so water behind it is very sheltered. silts are deposited here to form salt marshes/mud flats
how do bars form?
if a spit grows across a bay it can join two headlands together forming a bar, they can also trap shallow lakes behind the bar which are lagoons
what has been formed at swanage bay?
headlands and a bay
what are the 2 headlands at swanage bay called?
ballard point and durlston head
what is old harry (rock)?
a stack
what is chesil beach an example of?
a bar
what is the lagoon at chesil beach called?
the fleet
what is a berm?
ridges on the beach left as a mark of the tide
what is hard engineering?
building man-made artificial structures to control erosion and natural processes
what is a sea wall?
concrete wall placed at the foot of a cliff to prevent erosion
how does a sea wall prevent erosion?
it is curved so reflects wave energy back to sea
what are 2 advantages of sea walls?
good at protecting base of cliff, usually have promenades so people can walk along them
what are 2 disadvantages of sea walls?
waves are still powerful and can erode/break down the sea wall, expensive
approximately how much does one metre of sea wall cost?
£2000
what is rock armour?
large boulders placed at the foot of a cliff
how does rock armour prevent erosion?
breaks the waves and absorbs their energy
what are 3 advantages of rock armour?
cheaper than a sea wall, easy to maintain, can be used for fishing
what are 2 disadvantages of rock armour?
look different to other geology, expensive to transport rocks
what are gabions?
rocks held in mesh cages and placed in areas affected by erosion
what are 2 advantages of gabions?
cheap - approx £100 per metre, absorb wave energy
what are 2 disadvantages of gabions?
not very strong, look unnatural
what are groynes?
wooden/rock structures built at right angles into the sea
what are 2 advantages of groynes?
builds a beach which encourages tourism, trap sediment carried by longshore drift
what are 2 disadvantages of groynes?
by trapping sediment it starves beaches further down the coastline which increases erosion elsewhere, they look unattractive
what is soft engineering?
a more sustainable and natural approach to controlling erosion
what is beach nourishment?
sand is pumped onto an existing beach to build it up
what are 2 advantages of beach nourishment?
blends in with existing beach, larger beaches appeal to tourists
what are 2 disadvantages of beach nourishment?
needs to be replaced constantly, sand has to be brought from elsewhere
