Prelim Revision Coasts

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Prelim RevisionCoasts
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What you need to know

• Processes of erosion and deposition
• Features of Coastal Erosion and Deposition
• How they were formed
• Diagrams
• Recognise features on OS map
• Coastal Defence Systems

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Hydraulic Action
The force of waves hitting a cliff (or sea wall)
compresses water and air into cracks and joints.
This increase in pressure may lead to cracks
widening and pieces of rock breaking off.
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Abrasion
Rock fragments may be picked up by waves and
thrown against the rock face of cliffs by
subsequent waves. Sometimes the softer rock are
abraded more than the harder ones, giving a
striped appearance. Abrasion is most effective at
the base of cliffs.
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Wave attrition
Rock fragments are worn down into smaller and
more rounded pieces. Currents and tidal
movements cause the fragments to be swirled
around and to grind against each other. This
type of erosion produces pebble beaches.
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Corrosion (solution)
Salts and acids in sea water can react with rocks
, slowly dissolving them away.
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Rates of erosion depend on many factors

• Waves strength, frequency, height
• Weather frequency of storm conditions
• Geology of the coastline
• -type of rock

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Many erosion features are a result of rocks of
varying hardness occurring beside/below each
other. The DIFFERENTIAL EROSION between them
creates the landform. (Note that mass movements
may also be triggered as a result. )
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How Are Wave Cut Platforms Formed?

• Erosion is greatest when large waves actually
  break against the foot of a cliff.
• The foot of the cliff is undercut.
• As the undercut gets larger the cliff above
  becomes increasingly unsupported and in time
  collapses
• As this process continues the cliff will slowly
  retreat.
• The flat land left at the foot of the cliff is
  called a wave cut platform

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Cliffs and Wave Cut Platforms
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Copy this diagram and labels
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Erosion on a Sea Cliff
Note- for a cave to occur, there must be an area
of weakness in the cliff face.
1)The sea attacks the foot of the cliff and
erodes the areas of weakness
2) The crack gets larger and develops into a
small cave
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4) Further undercutting causes the arch to
collapse. This leaves part of the cliff detached
as a stack. Further undercutting causes the stack
to collapse.
3) The cave is widened and deepened until it
cuts through the headland to form an arch.
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An arch forms when the sea breaks through to the
other side of the headland.
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Close up of Duncansby Stacks
and Stump
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A Blowhole or gloup may form if the erosion
at the back of the cave breaks through the roof
to the top of the cliff.This usually happens
at hightide in stormy weather.
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Cove/Bay
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Formation of a Cove

• Coves form where rock bands of varying strength
  run parallel to the coastline.
• Initially, a narrow band of relatively strong
  rock forms the coastline, and behind this is
  found a band of a weaker rock,
• Waves act on weakest areas of the coast, such as
  cracks and joints, and eventually break through
  the strong rock, exposing the weak rock.
• The weak rock is quickly eroded by hydraulic
  action and abrasion,
• A circular shape is formed because waves travel
  through the narrow entrance and then disperse in
  the cove, causing equal erosion at all points of
  the cove shoreline.

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Coastal Deposition
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Waves

• Constructive
• Destructive

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LONGSHORE DRIFT
Splash zone
Backwash direction
Swash direction
High tide mark
Intertidal zone
Low tide mark
On-shore winds make waves approach at an angle
( swash), but they go back down ( backwash) at
right angles to the beach. What is the result of
this process?
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Sand Spits
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• How do Sand Spits form?
• Longshore drift moves large amounts of material
  along the beach until there is a sudden change in
  the direction of the coastline. The sand keeps on
  moving in the original direction, even though
  there is not a coastline to follow.
• The sea has to be relatively shallow and
  sheltered allowing the accumulation of sand
  usually beyond a headland.
• Sometimes a curve develops if the on- shore wind
  changes direction.
• Spits can become permanent if the prevailing wind
  picks up sand and blows it inland forming sand
  dunes.

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This spit will become a bar if it reaches the
other side of the estuary. Can you work out the
direction of longshore drift?
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• How Do Bars and Lagoons form?
• A bar is a barrier of sand stretching right
  across a sheltered bay (the spit has reached the
  other side of a bay).
• It usually stretches across the bay due to the
  absence of any large river that might wash it
  away.
• It can cut off a lagoon to the landward side.
• A lagoon is a body of brackish water- part salty,
  and part fresh. It often supports specialised
  plants and animals, and is protected as a nature
  reserve.

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If a bar links up with an off-shore island, it
creates a tombolo. Chesil Beach- one of the most
famous bars in the UK has a tombolo called
Portland Bill.
bar
tombolo
Chesil beach from Portland Bill the shingle is
29kms long.
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Coastal Defence Systems

• Sea Walls
• Gabions (wire cages with stones)
• Groynes
• Mappleton (stone groynes)

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Coastal Conflicts

• What you need to know
• social, economic and environmental impact of
  coastal land uses
• conflicts which can arise between these and other
  land users
• management strategies and solutions adopted to
  deal with such issues
• role of public and voluntary bodies in management
  of these strategies and solutions.

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Land Use in Coastal Areas

• Water sports
• Camping and Caravan sites
• Tourist Parking
• Recreation
• New Hotel building
• What are the environmental Problems?

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Environmental Conflicts

• Water polluted by boats discharging petrol
• Peace destroyed by noise of boats
• Parked boat trailer and other traffic may cause
  congestion

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Solutions

• Patrols to monitor water pollution
• Enforce speed restriction to reduce accidents
• Control over development - limits land uses such
  as infill sites which could destroy the
  environment
• Educational campaigns/adverts raise public
  awareness

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Dorset Case Study

• Conservation in Dorset
• National Nature Reserves
• Areas of Outstanding Natural Beauty
• Site of Special Scientific Interest
• Dorset Coast Park
• Dorset Wildlife Trust Reserves
• UNESCO World Heritage Sites
• Royal Society for the Protection of Birds Reserve
• Dorset Wildlife Trust

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Coasts map reading

• erosion1 coast map.pdf
• deposition1 coast os.pdf

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