Topic 4 - Coastal change and conflict Flashcards
How do waves and geology influence the coastline?
Waves are generated by wind blowing over the sea. Friction with the sur
face of the water causes ripples to form . The amount of energy in the
waves depends on their height which in turn depends on wind strength,
duration and the distance over which the wind has blown (fetch). As they
approach the beach they lose energy as the water surges up the beach
(swash) then runs back into the sea due to gravity (backwash).
Constructive waves
Gentle winds, short fetch, less
energy, deposition, low
height, 8-10 per min, strong
swash, weak backwash, wide
and shallow beaches offering
protection to cliffs absorbing
wave energy
Destructive waves
Strong winds, long fetch, pow
erful, cause erosion, steep, 11-15 per min, strong backwash,
weak swash, narrow and
steep beaches form offering
little protection to the cliffs
What is the geological structure of concordant and discordant coasts?
The UK’s coastline includes an number of distinctive landforms resulting
from wave action and physical processes interacting with the geological
structure and rock type. Concordant coasts display band of resistant and
less resistant rock that run at right angles to the coastline. Discordant
coasts have bands of resistant or less resistant rocks that run parallel to the
coastline.
How are headlands and bays formed?
Formed on discordant coasts where
rock resistance affects rates of ero
sion. E.g. Harder chalk rocks at Stud
land and limestone south of Swanage
can resist wave attacks and erosion
for longer and therefore stand out as
headlands unlike the soft clay of Swa
nage bay eroding much quicker to
form a bay. Fewer headlands and
bays exist on concordant coasts where
the rock if the same type along it’s
length. The hard rocks act as a barrier
but can be breached on lines of weak
nesses such as faults and joints cre
ating a cove, a circular area of water
with a narrow entrance from the sea.
What other forms of erosion are
created due to coastal erosion?
Seasons—low pressure in winter and
strong winds leads to more erosion
from high energy destructive waves.
Storm frequency– areas susceptible to strong storms are likely to suffer
with more erosion.
Prevailing winds—mainly from the south-west bringing warm moist air and frequent rainfall, this leads to more weathering and erosion
How do caves, arches, stacks and stumps form?
Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion.
As the waves continue to grind away at the crack, it begins to open up to form a cave.
The cave becomes larger and eventually breaks through the headland to form an arch.
The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).
The stack is undercut at the base until it collapses to form a stump.
How are wave cut notches/platforms created?
A wave-cut notch is created when erosion
occurs at the base of a cliff. As undercutting
occurs the notch gets bigger. The rock will
overhang the notch. The overhang will col
lapse and the cliff will retreat. This will create
a wave-cut platform which is visible during
low tide and submerged during high tide.
How fast is the coast changing?
Rates of erosion vary around the UK with
around 28% of the coastline is eroding more
than 10cm per year whilst other are eroding
much higher. It is not always a gradual process, landslips after storms are sudden losses.
What sub-aerial processes act on coastlines?
Weathering and mass movement weaken the cliffs above the high-water mark.
Physical/mechanical
(Freeze thaw)
During the day when temperatures are higher, the snow
melts and water enters the cracks in the rock. When the
temperature drops below 0°C the water in the crack freezes
and expands by about 9%. This makes the crack larger. As
this process is repeated through continual thawing and
freezing the crack gets larger over time. Eventually pieces
of rock break off.
Chemical
(acid rain)
slightly acidic rainfall, polluted by factories and vehicles,
reacts with weak minerals causing them to dissolve and
decay.
Biological
weathering
the roots of plants grow in cracks and split the rock apart as
do burrowing animals.
Rock falls
Sudden movement of rock from the cliff that has either
weathered or undercut causing the collapse
Sliding
loosened rocks and soil suddenly tumble down the slope
usually a bedding plane.
