Coastal Processes

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Coastal Processes
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• Creating waves
• Constructive waves
• Destructive waves
• Processes of erosion
• Processes of transportation
• Longshore drift
• - Summary

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• Creating waves
• Waves are created when the wind blows across the
  surface of the sea. The friction between the wind
  and the water pushes the water up into waves.
• The height and power of a wave depends on two
  factors
• the distance it has had to travel across open
  water to reach the coastline
• the wind speed.
• If waves have had to travel across a large area
  of open water, then they will have had time to
  gather energy and will have reached their full
  height. The length of the water over which the
  wind has blown is called the FETCH.
• Greater fetch strong wind more powerful wave
  with greater potential for erosion

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• Constructive waves have three main features
• They are low in proportion to their length
• They have a strong swash which carries material
  up the beach and and a weak backwash which
  doesnt take the material away
• They break gently, with only six and nine waves
  per minute

Constructive waves allow material to be deposited
along the coastline and form features such as
spits, tombolos and bars
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• Destructive waves have three main features
• They are high in proportion to their length
• The backwash is much stronger than the swash so
  that rocks, pebbles and sand are carried back to
  the sea
• They are frequent waves, breaking at an average
  rate of between eleven and fifteen per minute

Destructive waves erode the coastline and help
form features such as wave cut platforms,
headlands, bays, arches, stacks, caves and stumps
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Processes of erosion HYDRAULIC ACTION
Hydraulic action results from the weight of
water hitting the coast. Air trapped in cracks is
suddenly compressed by the breaking waves, which
increases the pressure on the rocks. This type of
erosion is greatest in storm conditions. CORRASION
(also called Abrasion ) Breaking waves throw
sand and pebbles against the cliff face which
scrape away at the rock. This can cause
undercutting at the base of a cliff. ATTRITIONPa
rticles are reduced in size as they collide with
the rock face and with each other in the breaking
waves. They become smaller and more
rounded. CORROSION (also called solution) This
is the dissolving action of sea water on the
rocks and it is most effective on limestone rocks.
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PROCESSES OF TRANSPORTATION Traction This is
when rocks and heavy boulders are dragged along
the sea bed. This would usually occur when the
waves do not have enough energy to carry the
material Saltation This is when smaller boulders
are bounced along the sea bed Suspension
Material such as sand grains, are carried along
in the water in suspension Solution Lime from
chalk and limestone rocks dissolves and is
carried in solution
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Longshore drift
The transport of sand and pebbles along the coast
is called LONGSHORE DRIFT Waves often approach
the coast at an angle and the swash carries the
sand and pebbles up the beach at the same angle.
The backwash, however carries the material back
down the beach at right angles as this is the
steepest gradient. This causes the material to
move along the coastline in a zig-zag motion and
the material will eventually be deposited when
the waves lose energy. The general direction of
longshore drift is decided by the prevailing wind
direction.
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• SUMMARY
• Constructive waves have a strong swash and a weak
  backwash so therefore deposit material on the
  coastline
• Destructive waves have a weak swash and a strong
  backwash so therefore erode material from the
  coastline
• The distance over the sea that the wind has
  blown when creating waves, is called the FETCH
• The four types of erosion are hydraulic action,
  corrasion, corrosion and attrition
• The four types of transportation are saltation,
  traction, solution and suspension
• Material can also be transported along the coast
  in the zig-zag movement called longshore drift