Example answer to Coastal landform 20 markers with all Coastal landforms such as cliffs, faults, caves, arch, stack, stump, coves, blowholes,wave-cut notch, geo,wave-cut platform, bays, and headlands include.
Faults are narrow zig-zag cracks in hard rock with an estimated height of 15m to 20m tall which form
all over the cliff. They are a small void in the hard rock of the headland which get wider and deeper
over time. Faults are formed by many key erosional, weathering processes and wave refraction. Wave
refraction is when waves bend to become parallel to the coastline. The shallower water around the
headlands causes the waves to slow down because of friction. The waves then concentrate at convex
points such as headlands. These waves have increased energy which means more erosion causing
the faults to widen. Hydraulic action is when the sheer power of the waves smash against the cliff. Air
gets trapped in the rocks which causes cracks in the rock due to the pressure. This creates the fault.
Abrasion erodes the hard rock cliff-face further widening the fault. Abrasion is the process of rocks
hitting the cliff and eroding the hard rock away. Wave quarrying also contributes to the fault widening
as the joints enlarge as large chunks of rock are removed by vibration. Weathering effects the top part
of the cliff-face where the fault can’t be eroded by the sea. Freeze thaw weathering is when water
enters the permeable rock, then the temperature decreases which freezes the water thus expanding
the rock causing cracks to widen. The process repeats itself until the rocks break apart. Biological
weathering also helps form the fault as vegetation on the cliff can affect the cracks. Tree roots can
exert stress on cracks as the roots expand and grow they create and widen cracks. Chemical
weathering such as carbonation occurs. Carbonation is the process of rainwater absorbing carbon
dioxide, from the air to form a weak acid. When the rain falls it reacts with minerals in the rock and
dissolves them. Faults occur at discordant coastlines or concordant as an area of hard rock is
needed. Discordant coastlines are coastlines with more then two types of rock in vertical bands
whereas concordant coastlines are coastlines with only one type of rock.
Cave
Caves are wide, circular concave landforms which form at the base of a cliff-face below a Geo. Caves
can be between 5m to 20m long and 2.5m to 10m deep. They are a large void in an area of hard rock.
A cave forms when an already weakened area of hard rock is continually eroded by wave refraction
and the erosional processes of hydraulic action plus abrasion. Wave refraction is when waves bend to
become parallel to the coastline. The destructive waves refract and converge at convex areas. The
waves concentrate their high energy on the sides of the headlands meaning that the hard rock will
erode faster. The cave is also deepened by the process of hydraulic action which is when high energy
waves smash against the cliff causing cracks. The water enters the cracks and the pressure rips the
rock apart. Abrasion is when sediment hits against the rock at a high velocity causing the rock to
erode at a fast pace. These processes will work together to erode the hard rock causing a deep cave.
They form on discordant coastlines as an ill regular coastline is needed for wave refraction and as
caves form on headlands. Headlands and bays form on discordant coastlines as they need two types
of alternating bands of rock.
Arch
Arches are tall, wide, oval concave landforms which are approximately 30m tall and 5m wide. They
form in the headland towards the end, behind a wave cut notch and in front of a cave. Arches are
voids in hard rock which have been eroded by processes such as abrasion, hydraulic action. Wave
refraction helps the formation as it will erode two aligned caves until they break through into an arch.
Wave refraction is when headlands are eroded by high energy destructive waves which converge at
both sides. The waves bend to become parallel to the coastline. This creates cracks and erodes the
hard rock into a cave. Surge channels help erode the two caves so deeply that they become an arch.
The hard rock can also be eroded by hydraulic action. Hydraulic action is when the force of the waves
hitting the hard rock and going into the cracks which, causes high pressure in the rocks splitting them
apart. Abrasion helps the erosion of the caves into arches. Abrasion is the process of sediment which
hits the hard rock at a high-speed causing the rocks to crumble and erode. Sub-ariel and biological
weathering help form the arch. Freeze thaw weathering is when water enter cracks in the rocks. The
temperature then drops and the water freezes making the cracks expand and new cracks form.
, Biological weathering such as animals borrowing under the ground creating holes and cracks in the
cliff thus weakening the rock, so it crumbles more.
Stack
A stack is offshore of a headland and behind a stump. It is very isolated. A stack can be between
30m-40m tall and about 5m wide. It is quite narrow and elongated with a narrowing base due to
erosion. Made from hard rock such as chalk/limestone. A stack can be formed by weathering
processes such as freeze thaw, carbonation and hydration which weaken the roof of the arch causing
it to change into a stack. The increase pressure on the roof can also be because of the erosion at the
base of the stack. The roof of the arch is weakened by sub-ariel weathering processes of freeze thaw
weathering. Freeze thaw weathering is the process of water entering permeable rocks through cracks,
then the temperature decreases which freezes the water causing the cracks to expand from the
pressure put on the rock. The water makes it deeper into the cracks thus repeating the process. The
chemical weathering process of hydration weakens the rock. Hydration is when water is absorbed by
rock then, dries forming crystals which exert pressure causing the rock to crumble. Carbonation also
weakens the rock, rainwater that has absorbed carbon dioxide and nitrous oxide from the atmosphere
creating a weak acid. The slightly acidic rainwater dissolves the minerals in rock causing in to
crumble. Biological weathering such as bacteria and algae produce chemicals which help break down
the rock as they live here. Mass movement contributes as rockfall occurs as there is a steep gradient,
so it falls fast. It falls under its own weight because of gravity. The roof arch falls to form the stack as
its unstable.
Stump
A stump is formed next to a stack and offshore of a headland. Stumps are approximately 10m tall and
5m wide, so short, wide and rectangular. The sides are usually quite jagged. Made of hard rock such
as chalk/limestone. A stump is formed by wave cut notches being eroded into the base of a stack
exerting pressure on the weathered rock at the top of stack. Wave cut notches are formed at the base
of the stacks by corrasion. Corrasion uses the sediment from the roof of the arch which has crumbled.
The sediment is thrown against the base of the stack which erodes the rock away. This creates an
unstable base of the stack which puts extra pressure on the top of stack from gravity. The top of the
stack is weathered by sub-ariel weathering such as freeze thaw. Freeze thaw weathering is when
water enters the cracks and freezes then, the temperature drops causing the cracks to expand. This
process will repeat itself till the rocks split apart. Biological weathering is also involved in weakening
the rock. Seagull excrement will weaken the rock as it slightly acidic, so the chemicals erode the
minerals of the rock. These processes will significantly weaken the rock which causes the rock to
become unstable. This means that the rock will collapse under its own weight as the process of
rockfall takes place. Rockfall is a type of mass movement where the rocks fall from a steep gradient.
When the rockfalls the stack become a stump.
Coves
A cove form on a concordant coastline. A concordant coastline is a coastline with only one rock type
which is relatively straight. It is formed behind a coast between horizontal alternating bands of hard
rock e.g. chalk/limestone and soft rock e.g. sandstone/clay. It is a void in an area of soft rock which
has a beach and water in it. They are usually 100m-500m wide and 300m deep. Quite circular, they
tend to be wide in the middle and narrow at the entrance. Waves seek out faults in the hard rock so
that the hard rock can be eroded easier. Corrasion occurs as sediment is carried by waves and then it
hits the hard rock causing it to crumble and erode. Hydraulic action is when the force of waves power
smash against the hard rock causing cracks which erodes the rock. The hard rock is harder to erode
so it is a narrower entrance them the wide bay. The soft rock is eroded faster by the process of
hydraulic action and corrasion. The waves are also refracted within the cove causing high energy
destructive waves to erode in all directions.
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