Transcript File

Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Waves
• Responsible for erosion, transportation and deposition
of material along coastlines
• Generated by wind passing over the surface of the sea
• Fetch is the open area of the sea that a wave travels
over
• The longer the fetch, the stronger the wind speed, the
stronger and greater the waves generated
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Factors affecting the rate of coastal erosion
Where the breaking of a wave occurs
1. Steepness of the wave
2. Rock resistance
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Types of waves
1. Constructive waves
2. Destructive waves
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Wave refraction
•
Waves slow down as water becomes shallow
•
Waves bend and change their direction as they
approach the shore
•
Causes waves to move towards the headland where
their erosive force is released
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Longshore drift – a process of coastal transportation
The sea transports its load of sand and shingle in
two main ways:
1. Up the shore in swash
2. Back down the shore in backwash
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Processes of coastal erosion
•
Geology of the coastline determines the rate of
erosion
•
Soft rock, e.g. chalk, is eroded faster than harder
more resistant rock, e.g. igneous rock
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Processes of coastal erosion
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Hydraulic action
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Compression
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Abrasion/corrasion
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Attrition
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Solution/corrosion
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
1. Cliffs
•
Cliffs are vertical slopes on a coastline
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Form as a result of a combination of coastal processes of
erosion, such as hydraulic action, compression, abrasion,
solution and attrition
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Destructive waves attack an area of weakness in rocks
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Crack/joint forms
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Crack/joints are attacked by hydraulic force of the
water and by compression
•
Notch forms
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
1. Cliffs (continued)
•
Notch gets bigger, eventually the rocks above the notch
are unsupported and collapse to form a cliff
•
Shattered rock falls into the sea
•
Sea uses this shattered rock to further erode the cliff
through abrasion
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Solution also erodes the cliff face
•
These events continue over time and the cliff face
retreats
•
Wave-cut platforms – surface of rock that remains in
front of the retreating cliff
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Wave-built terraces – deposited pieces of rock that are
deposited below low-tide level
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
2. Bays and headlands
•
Differential erosion – rocks along coastlines are eroded
at differing rates depending on whether they are soft or
hard
•
Sections of coastline that are composed of soft rock will
erode faster than areas composed of hard, more
resistant rock
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Stretches that are composed of soft rock will form bays
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Harder more resistant rock will take longer to erode and
will remain jutting out into the sea as headlands
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
3. Sea caves, sea arches, sea stacks and sea stumps
•
Caves form in an area of weakness on a cliff face or
headland
•
Processes of coastal erosion act on this area of weakness
and enlarge it to form caves
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Caves are further eroded by abrasion, resulting in them
becoming larger
•
Sea arches form when continued erosion occurs in a sea
cave causing it to extend right through the headland
•
A sea arch may also form when two sea caves form back
to back on the opposite sides of a headland
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
3. Sea caves, sea arches, sea stacks and sea stumps
(continued)
•
A sea stack is a rock which is standing out in isolation in
the sea away from the coastline
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Sea stacks form when erosion continues on a sea arch,
widening the sea arch and causing the roof of the sea
arch to eventually collapse
•
When the roof of the sea arch collapses, it leaves the
former section of headland isolated or cut away from
the main headland/coast. What remains standing out in
the sea in isolation is called a sea stack
•
A sea stump is the eroded remains of a sea stack
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal erosion
4. Blowholes
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Blowholes form at areas of weakness, for example,
where a hole forms on the surface of a cliff top joins
with a roof of a sea cave. They are formed as a result of
compression
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Air may become trapped in a sea cave by waves
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Results in a build up of pressure which leads to rock
shattering the rocks of the cave roof
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Rock eventually collapses creating a ‘blowhole’
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Processes of coastal deposition
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Coastal deposition occurs when waves lose energy and
therefore their ability to carry material
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Sea deposits its load on the coastal area
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Constructive waves have an ability to move the load
inland
•
Wave refraction in bays result in wave energy
decreasing and this results in deposition occurring
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Deposited material may include shingle, sand and
sediment
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
1. Beach
•
A beach is an area of sand and gravel located in an area
between high tide and low tide mark
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Waves move up the sea shore, slow down and their load
of sand and rocks is deposited
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Heavier load of rock and shingle is deposited on the
backshore
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Finer, lighter material such as sand is deposited on the
foreshore
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Over time a beach is formed
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A storm beach forms when waves are strong enough to
push large rocks and boulders above the high tide mark
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
2. Sand spit
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A sand spit is a long narrow ridge of deposited sand and
shingle that is connected to the coast at one end
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Sand spits develop due to longshore drift and deposition
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Sand spits form where the process of longshore drift is
interrupted
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Sediment is deposited in sheltered and shallow water
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Over time this sediment builds up and becomes visible
above the level of the sea
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
2. Sand spit (continued)
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On the seaward side of the sand spit constructive waves
deposit fine sediment such as sand and form a beach
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Over time the sand spit gets wider
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As sand spits grow the area of water behind it is often
then sheltered by waves and wind
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This often leads to the formation of a salt marsh
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Wave refraction may occur at the end of a sand spit
which results in the sediment being carried around the
end of the sand spit to form a recurved spit (i.e. hook)
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
3. Sand bar and lagoon
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A sand bar forms when a sand spit extends across a bay
and over time connects two land masses
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Sand bars will eventually seal off an area of coastline
and the water directly behind the sand bar will then be
called a lagoon
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
3. Sand bar and lagoon (continued)
There are two types of sand bar:
1. Offshore bar

Located away from the coastline

Parallel to the coastline

Generally only exposed at times of low tide

Breaking waves deposit sand on the offshore bar

Size of the offshore bar increases over time

May eventually block or close off the bay creating a lagoon
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
3. Sand bar and lagoon (continued)
2. Baymouth bar

Sand spit extends from one side of a landmass across a bay
and reaches the other landmass

Blocks/closes off the bay
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Landforms of coastal deposition
4. Tombolo
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Tombolos are formed due to wave refraction and
longshore drift
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Result from a sand spit extending out to an island and
connecting the island to the mainland
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Waves approach the island, wave refraction occurs
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Sediment is deposited
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Results in the spit connecting the island to the mainland
and – a tombolo is formed
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Human activities can impact on the operation of
coastal processes
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The impact of recreational pressures
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Caravan parks, camping sites and hotels or even
apartments may be unwisely and hastily built
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Sand dunes damaged
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Sewage and litter
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Pollution
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Coastal defence work
1. Groynes
2. Rock armour
3. Sea walls
4. Breakwaters
5. Gabions
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Conservation and management case study
Increasing rates of coastal erosion may be attributed to a
number of factors:
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Rising sea levels
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Increasing storm frequency
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Increasing wave energy
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Erosion may be caused by the following:
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People
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Nature
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Advantages of beach nourishment
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Restores and widens existing beaches
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Infrastructure and property at the back of the beach is
protected
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Beach nourishment places sand on the beach
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Disadvantages of using beach nourishment
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Sand pumped onto beaches through beach nourishment
usually erodes faster than the natural sand
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Expensive and must be repeated
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Visitors and marine life impacted during beach
nourishment pumping
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Sand dune management
Erosion and damage may be caused by the following:
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Wind
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Water
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Human activity
Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction
Protection of sand dunes
The action taken includes the following:
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Planting/re-establishment of vegetation
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New sand dune formation encouraged
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Screens and fences trap sand that is blown inland
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Grass and shrubs are planted on the sand dunes to
ensure stability
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Timber pathways laid down