coastal systems - coastal landscape development Flashcards
what factors affect the cliff profile and its rate of retreat
the balance between marine factors - wave energy, fetch presence of a beach - and terrestrial factors - subaerial processes, rock geology and lithology
most rapidly retreating cliffs composed of very weak rock
rising sea levels
human activities - coastal defences elsewhere leading to increased erosion
where do steep cliffs occur on a coastline
tend to occur where rock is strong and resistant to erosion - igneous and metamorphic rocks
sedimentary rocks that are dipping steeply or vertically tend to produce steep and dramatic cliffs, as well the absence of a beach and an exposed orientation with a long fetch and high energy waves that encourage erosions and undercutting by the sea
where do gentle cliffs occur on a coastline
usually reflect weak or unconsolidated rocks that are prone to slumping
rocks dipping towards the sea tend to have low angle cliffs
sheltered location with low energy waves and a short fetch will result in subaerial debris building up at the foot of the cliff, reducing its overall angle
wide beach will absorb wave energy, prevents significant undercutting and steepening
weathering and mass movement - rock prone to weathering and mass movement will be subject to sever erosion
wave energy - high energy waves driven by strong prevailing winds and a long fetch will increase the rate of retreat
how do caves, arches, stacks and stumps form
erosion of rocks like limestone and chalk tend to exploit any lines of weakness - joints, faults, cracks
joints and faults eroded by hydraulic action and abrasion, widening them forming a cave - if overlying rock collapses this creates a blowhole
cave enlarged by hydraulic action and abrasion
erosion eventually cuts through headland or two caves join up an arch is formed
base or arch is widened and the ap is further enlarged by erosion and weathering
roof of arch collapses due to gravity and lack of support levin an isolated pillar or rock called a stack
stack continues to be eroded by the sea, weathering, abrasion, hydraulic action and will eventually collapse to leave a stump (may only appear above the surface at low tide)
what factors affect the amount of erosion
wave strength - determined by fetch and wind speed
landforms - wide beaches dissipate wave energy before it reaches the cliff
human activities e.g. groynes
geology of coastline
frequency of storm events
amount of weathering - makes cliffs weaker
bathymetry of the sea bed - also determines wave strength at the coasts
what is a discordant coastline
band of different rock type run at right angles to the coast, differing resistance to erosion leads to formation of headlands and bays
what is a concordant coastline
layers of differing rock type run parallel to the coastline, outer hard rock provides a protective barrier to erosion of softer rock further inland
coves may form is erosion occurs
what is coastal morphology
the shape of the landscape features and is determined by geology (rock type) and lithology
what is litholoy
Strata - layers of rock
Bedding planes - horizontal, natural breaks in strata, caused by haps in time during periods of rock formation.
Joints - vertical fractures caused either by contraction as sediments dry out, or by earth movements during uplift.
Folds - formed by pressure during tectonic activity, which makes rocks buckle and crumple
Faults - formed when stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). The faults then slip or move along fault planes.
Dip - the angle at which rock strata lie
what is differential erosion
the different rates of erosion the occur along a coastline due to geological factors such as the resistance of the rock and structural weaknesses
what medium/large landforms are created on a coastline where there is resistant rock
areas of higher relief
cliffs
headlands
what medium/large landforms are created on a coastline where there is weak rock
lowland areas
bays
inlets
what small landforms are created on a coastline
Within same rock outcrop geological weaknesses are eroded more quickly.
If internal rock has the strength, sea caves will develop and can extend vertically to form blowholes.
Other weaknesses by be eroded to form geos (a small inlet at the coast).
Bands of more resistant rock between weaker cracks will erode more slowly to form small headlands 🡪 arches 🡪 stacks 🡪 stumps.
how are headlands and bays formed
alternate layers of more resistant and less resistant rock
differential erosion erodes less resistant rock faster leaving bays
headlands left sticking out into sea
due to wave refraction deposition occurs at back of bays forming a beach
wave energy gets concentrated around headlands due to wave refraction = more erosion = coves arches, stacks, stumps
how are coves formed
along concordant coastlines
weaknesses in more resistant rock will be exploited by hydraulic action and start to erode it - erosion will occur slowly
more resistant rock eventually eroded through completely
the sea erodes the less resistant rock at a faster rate through hydraulic action and abrasion forming a cove
erodes until it reaches the more resistant rock layer - this forms the back wall of the cove
how are wave cut platforms formed
between the low and hight tide mark hydraulic action exploits the weaknesses in the more resistant rock
at the top of the cliff weathering occurs weakening the cliff top
a wave cut notch is formed in between the high tide and low tide mark by hydraulic action exploiting the weaknesses and abrasions wearing away the cliff
the cliff collapses due to no support from the base of the cliff and being weakened at the top
weathering continues to weaken the cliff
a new wave cut notch is formed through hydraulic action and abrasion
cliff continues to collapse and process keeps on repeating until a wave cut platform is formed - a rocky platform that is exposed at low tide and covered at high tide, platform can be eroded by abrasion and solution as the tide moves over it
wave cut platform will dissipate the energy of the wave so less erosion will occur on the cliff face as erosive power at the base of the cliff declines and the rate of retreat slows, erosion will still occur during a storm when the waves are stronger
what erosional features occur in the early stages of the erosion cycle
notches
caves
geos
blowholes
what erosional features occur in the middle stage of erosion cycle
stacks
stumps
bays
headlands
arches
what erosional feature occur at the late stages of the erosional cycle
wave cut platform
on a low energy coastline where does the beach material get sourced from
cliff erosion - 5%
offshore - 5%
river - 90%
what are the characteristics of a low energy coastline
waves are not powerful
deposition exceeds erosion
landforms include beaches and spits
estuaries, inlets and sheltered bays - wave energy is dissipated
where do beaches occur
on low energy coastlines
sand and shingle accumulate faster that they are eroded
coastline dominated by constructive waves
what are beaches
accumulation of material deposited between position of the lowest tide and highest storm waves
beach material - sand, shingle, pebble
what are the inputs to a beach
beach nourishment
cliff and dune erosion
fluvial sediment
longshore transport
onshore transport (swash)
what are the outputs to a beach
off shore transport (backwash)
sand mining
longshore transport
offshore wind transport
storm events
what factors affect beach profiles
sediment size
wave type
how does sediment size affect a beach profile
beaches have different gradients according to their material
Sand produces beaches with a gentle gradient (<5 degrees)
Shingle produces beaches with steeper gradient (10-20 degrees)
how does wave type affect the beach profile
Destructive waves = stronger backwash = more material moving back down the beach = shallower profile (unless storm beach).
Constructive waves = strong swash = more material moved up the beach = steeper beach profile.
Wave type often vary with the season so the beach profile can change between the winter and the summer.
what is a swash aligned beach
produced where the waves break in line (parallel) with the coast.
Swash & backwash movements move material up and down the beach producing beach profile features.
smoothly curved, concave beaches.
beach face is orientated parallel to the fronts of the dominant waves.
Beaches which face the waves
what are drift aligned beaches
where waves break at an angle to the coast.
swash occurs at an angle but backwash runs perpendicular to the beach.
material is transported along the beach via longshore drift
what amount of coastlines are depositional and what amount suffer from net erosion
20% depositional
80% suffer from net erosion
what are the parts of a beach
backshore
foreshore
nearshore
offshore
what is the backshore of a beach
the part of the beach lying between the beach face and the dune foot or the coastline
what is the foreshore of a beach
part of the shore/beach which is wet due to the varying tide and wave run up under normal conditions
what is the nearshore of a beach
sone which extends form the foreshore to the lower shore face
where waves break
what is the offshore of a beach
the zone off the shoreface
waves not broken yet
what are features you can find on a beach
ridges and runnels
ripples
cusps
berms
storm beach
what are rides and runnels
Series of ridges and troughs running parallel to the coast near the low water mark.
ridges are formed by deposition during backwash and runnels are formed when
water runs back to the ocean.
can be broken by drainage channels.
what are ripples
relatively small, elongated ridges that form on the beach
Waves and currents flow across loose sand which is dragged along the bottom and is piled up to form ripples
what are cusps
Semi-circular shaped depressions with coarser material around the edge and finer material in the middle.
Formed by a collection of waves reaching the same point and backwash scouring out the finer material in the centre.
what are berms
Small ridges that form near high tide mark
Deposited by the swash of constructive waves
Can be a series of berms along the beach that
indicate the weekly high tide cycle between spring and neap tides
what are storm beach
ridge found near the back of the beach composed of larger sediment
Deposited by waves during storm events – waves don’t usually affect this part of the beach.
