Coasts Revision

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					Prelim Revision
    What you need to know
• Processes of erosion and deposition
• Features of Coastal Erosion and
  – How they were formed
  – Diagrams
• Recognise features on OS map
• Coastal Defence Systems
                   The force of
Hydraulic Action   waves hitting a
                   cliff (or sea wall)
                   compresses water
                   and air into
                   cracks and
                   This increase in
                   pressure may
                   lead to cracks
                   widening and
                   pieces of rock
                   breaking off.
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
Abrasion is most
effective at the base of
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
       This type of erosion
       produces pebble
Corrosion (solution)

             Salts and acids in
             sea water can
             react with rocks ,
             slowly dissolving
             them away.
Rates of erosion depend on
      many factors:
• Waves – strength, frequency,
• Weather – frequency of storm
• Geology of the coastline :
    -type of rock
Many erosion features are a
result of rocks of varying
hardness occurring
beside/below each other. The
between them creates the
(Note that mass movements
may also be triggered as a
result. )
  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
Cliffs and Wave Cut Platforms
Copy this diagram and labels
            Erosion on a Sea Cliff

                                                      Note;- for a
                                                      cave to
                                                      occur, there
                                                      must be an
                                                      area of
                                                      weakness in
                                                      the cliff
1)The sea attacks the      2) The crack gets larger
  foot of the cliff and   and develops into a small
 erodes the areas of                cave
                                         4) Further undercutting causes the arch
3) The cave is widened and deepened
                                          to collapse. This leaves part of the cliff
 until it cuts through the headland to
                                               detached as a stack. Further
              form an arch.
                                             undercutting causes the stack to
An arch
forms when
the sea
through to
the other
side of the
Close up of Duncansby Stacks
         and Stump
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 high
   tide in stormy weather.
          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.
Coastal Deposition
• Constructive
• Destructive
  Swash direction                      High tide mark

                                            Low tide

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
Sand Spits
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
•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.
This spit will become a bar if it reaches the other
side of the estuary. Can you work out the direction of
longshore drift?
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.
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.

                         Chesil beach from Portland Bill;
                         the shingle is 29kms long.
   Coastal Defence Systems
• Sea Walls
• Gabions (wire cages with
• Groynes
• Mappleton (stone groynes)
           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.
    Land Use in Coastal Areas
•   Water sports
•   Camping and Caravan sites
•   Tourist Parking
•   Recreation
•   New Hotel building

• What are the environmental Problems?
    Environmental Conflicts
• Water polluted by boats discharging
• Peace destroyed by noise of boats
• Parked boat trailer and other traffic may
  cause congestion
• Patrols to monitor water pollution
• Enforce speed restriction to reduce
• Control over development - limits land
  uses such as infill sites which could
  destroy the environment
• Educational campaigns/adverts raise
  public awareness
          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
• Dorset Wildlife Trust
        Coasts map reading
• erosion[1] coast map.pdf
• deposition[1] coast os.pdf