Transcript Coastal Landforms - MSP Humanities at IISB

Coastal Processes
and Landforms
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Why are waves generally larger in the south west than
in the south east?
Wave energy depends on the
fetch, the strength of the
wind and the length of time
over which the wind has
blown.
fetch = the distance over
which the wind has blown
Look at an atlas or a wall map to find out the
largest fetch around the British Isles.
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Why do waves break?
wavelength
the bottom of the wave touches the sand, slows
down and the top of the wave topples over
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Why do waves break?
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Swash and backwash
Backwash
Swash
Note: Backwash is always at right angles to the beach
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Waves can be destructive or constructive.
When a wave breaks, water is washed up
the beach - this is called the swash. Then
the water runs back down the beach - this is
called the backwash. With a constructive
wave, the swash is stronger than the
backwash. With a destructive wave,
the backwash is stronger than the swash.
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Types of waves
Destructive Waves
Backwash stronger than swash
Constructive Waves
Swash stronger than backwash
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Processes of erosion
Corrosion
Hydraulic action
Processes of erosion
Attrition
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Abrasion
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Attrition
Material carried by the waves bump into each other and so are
smoothed and broken down into smaller particles.
Hydraulic action
This process involves the force of water against the coast. The
waves enter cracks (faults) in the coastline and compress the air
within the crack. When the wave retreats, the air in the crack
expands quickly causing a minor explosion. This process is
repeated continuously.
Corrosion
This is the chemical action of sea water. The acids in the salt
water slowly dissolve rocks on the coast. Limestone and chalk are
particularly prone to this process.
Abrasion/Corrasion
This is the process by which the coast is worn down by material
carried by the waves. Waves throw these particles against the
rock, sometimes at high velocity.
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Dorset coastline
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Landforms of coastal erosion
1) Headlands and Bays
2) Cliffs and Wave Cut Platforms
3) Caves, Arches, Stacks and Stumps
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Headlands and bays
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An example of headlands and bays on the
Dorset coastline…
chalk
clay
Swanage
Bay
limestone
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Cliffs
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Wave-cut platform
The waves attack the base of the cliff through the processes
of abrasion, corrosion, hydraulic action and attrition.
Over time the cliff will be undercut and a wave-cut notch is
formed.
Eventually the cliff becomes unstable and collapses. Further
cliff retreat will form a wave-cut platform.
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Wave-cut platform – Burgh Island, Devon
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Caves, arches, stacks and stumps
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Caves, arches, stacks and stumps
Match the image with the most appropriate label.
A
B
1
C
3
D
2
4
1. The waves erode FAULTS (cracks) in the headland.
2. The waves eventually erode through the headland to
form an ARCH.
3. The arch becomes unsupported and collapses to
form a STACK.
4. A STUMP is formed from the collapsed stack.
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If these photos were taken of one headland over time,
which of these landforms would be the first to be formed?
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Coastal processes – transportation
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Longshore drift
Direction of movement
Backwash is always at
right angles to the beach
swash
Backwash
This movement of sediment along the
coastline is called longshore drift.
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Landforms of coastal deposition
1) Beaches
2) Spits
3) Tombolos and Bars
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Spit formation
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Spit formation
Why is the spit curved?
The wind direction changes and moves the spit inland. In
storm conditions the spit may be breached.
Why doesn’t the spit grow across the estuary to form a bar?
The river’s current stops deposition across the estuary.
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Tombolos and bars
The mainland is joined
to the Isle of Portland.
If a spit joins the mainland to an island it is called a
tombolo.
This diagram show the tombolo – Chesil Beach.
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Chesil beach
Chesil Beach
Isle of Portland
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Tombolos and bars
If a spit joins one part of the mainland to another it is
called a bar.
For example, there is a bar at Orford Ness in Devon.
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Groynes are used to stop LSD
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Humans are affected by the
retreat of the cliff (loss of land,
housing, etc.) They erect sea
defences
which
stop
the
erosion (groynes).
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How do groynes work?
Groynes trap the sand which is carried along the coast by
longshore drift.
The sand acts as a natural protection against the force of the
waves. The waves break on the beach and not the cliffs.
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c) Points for Groynes construction:
•It protects the coastline and preserves peoples: property
•Groynes encourage a beach to grow which can help
tourism and bring money to the area
Against: Groynes
•Looks very ugly
•Very expensive to build
•No guarantee it will last forever
•Some people suffer if groynes are built and sediment is
trapped .
•Divide the beach up into unnatural sections
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Explain the processes that have caused
this cliff to collapse.
C
C
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Erosion or deposition?
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8 Coastal Landscapes and Processes
(a) Study Figure 12a, on the insert, a photograph of Flam borough Head on the east coast
of England. Figure 12b is a sketch of the photograph.
Figure 12b
(i) On Figure 12b, mark with an arrow and label three coastal features shown in
Figure 12a.
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Caves, arches, stacks and stumps
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Bays and Headlands
Ans 4) Headlands and Bays form along DISCORDANT
coastlines where rocks outcrop at 90o to the coast
2. Here there are alternate bands of resistant and
less resistant rock
3. Where there is soft rock (e.g. clay), erosion is rapid
- and bays are formed (indent in coastline)
4. Where there is more resistant rock (e.g. chalk),
erosion is much slower - headlands are formed as
the harder rock is left sticking out into the sea
5. Exposed headlands then become vulnerable to
destructive waves but help to shelter neighbouring
bays.
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d)What is a spit formation?
SPIT = is a hooked shaped landform which typically runs
along a coastline formed where a river estuary meets the
coast. It is formed by the process of Longshore Drift bringing
material along the coastline in a zig-zag fashion. A saltmarsh
often forms behind the spit as the sediment can build up here
in shallower waters.
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Key Ideas
Waves are the result of the wind blowing over the sea. They break as
they approach land.
Swash and backwash describe the movement of a wave on the beach.
Fetch is the distance that the wind has travelled.
Sub-aerial processes such as weathering and mass movement occur on
the cliff face.
Coastal processes of erosion include hydraulic action, attrition,
corrosion and solution.
Landforms created by erosion include headlands and bays, caves,
arches, stacks and stumps.
Longshore drift is a method of coastal transport.
Landforms created by deposition include beaches, spits, tombolos and
bars.
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