Coasts - Coastal Processes

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Erosion - Hydraulic Action

The force of water against the coast. The waves enter cracks 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 and breaking some of the rock off. This process is continuous.

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Erosion - Solution

This is chemical action of sea water. The acids in salt water slowly dissolve rocks on the coast. Limestone and chalk are particularly prone to this. 

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Erosion - Abrasion

This is the process by which the coast is worn down by material caried by the waves. The waves throw these particle against the rock sometimes at high velocity.

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Erosion - Attrition

Material carried by the waves bump into each other and so are smoothed and broken down into smaller particles.

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Factors Affecting the Rate of Erosion

1. GEOLOGY = (rock type) Weaker rock such as till erodes faster then stronger rock such as granite

2. WHERE THE WAVES BREAK = Waves which break at the foot of the cliff erode more than waves that break further down the beach as their energy has dissipated

3. WAVE TYPE = steeper waves carr more energy which means they erode more, compared to shallower waves that don't have as much energy.

4. STEEPNESS OF BEACH = steep beaches allow waves to approach unimpeded (non obstructured) meaning they can erode more easily, compared to shallow beaches that act as a buffer, so waves can cause less erosion

5. BEACH TYPE = coarse shingle allows more infiltration meaning waves have a weak backash and less erosion occurs. Fine sandy beaches allow little infiltration which means waves have a strong backwash and erode more easily

6. FETCH = long fetch = more erosion as waves have more energy                                          short fetch = less erosion since waves have less energy

7. SHAPE OF COASTLINE = concordant = parallel  and discordant = perpendicular

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Helps to weaken rock making it more succeptable to erosion and mass movement, it however DOES NOT break down the rock

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Weathering process - Sub-Aerial weathering

(Otherwise known as physcial weathering) 

Disintegration of rocks into smaller particlces 


  • Rain
  • Freeze-thaw
  • Surface runoff
  • Pressure release
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Weathering process - Biological weathering

Weathering resulting from organic agents 


  • Burrowing organisms 
  • Tree and plant roots 
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Weathering process - Chemical weathering

Decomposition resulting from a chemical change 


  • Solution
  • Salt crystalisation
  • Acid rain
  • Oxidation
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Mass Movement

The downhill movement of all weathered material in response to gravity 

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Mass Movement - Soil Creep

VERY SLOW the soil moves less than 1cm per year in 3 different ways:

  • Raindrop Impact = causes particles to splash and drop downstream
  • Wet Periods = soil particles swell and move downhill under gravity when the soil dries
  • Freeze-thaw = water expands and heaves particles up and right angles. When they thaw the paticles fall downhill under gravity
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Mass Movement - Soliflucation

Occurs in tundra areas where soils are frozen for around 9 months of the year and vegetation is sparse. The top soil briefly thaws in the summer months and due to the lack of vegetation and additional water an ACTIVE FLOWING LAYER IS PRODUCED

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Mass Movement - Earthflows

Faster moving than soil creep at 5 to 15km per year and occurs on steep slopes (5 to 15 degrees). The movement occurs where the ground has become saturated, producing bulging lobes of soil. 

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Mass Movement - Mudflows

Slightly faster than Earthflows, with the speed at around 1km per hour on steeper slopes. They still produce bulging lobes of soil and they are commonly found on unconsolidated land after heavy rainfall. 

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Mass Movement - Slides and Slumps

Slides = maintain their internal structure and move as a large mass.

Slumps =  can appear to have a rotational element, producing a curved ruptured surface. Cliffs formed of weak impermeable rock e.g. clay are especially succeptable to rotational slumping after periods of prolonged rainfall, where the raised water table lubricates particles, facilitating cliff failure. 

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Mass Movement - Rockfall

Rapid movement of rock where slope exceeds 40 degrees. Result from extreme chemical or physical weathering. Produces debris slopes beneath the cliff as material from the rockfall disintegrates at foot of cliff. 

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Mass Movement - Runoff

Moves fine material such as silt and clay particles down slopes especially where there is a continuous flow of water. This is best seen in areas where there is little vegetation to anchor particles or impede runoff. 

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Transportation - Solution

Minerals are dissolved in sea water and carried in solution. The load is not visible. The load can come from chalk cliffs and calcium carbonate is also carried in the load

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Transportation - Suspension

Small particles are carried in the water e.g. clays, which can make the wate look cloudy. Currents pick up large amounts of sediment in suspension during a storm. 

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Transportation - Saltation

The load is bounced along the sea bed e.g. small pieces of shingle or large sand grains. Currents cannot keep the larger particles afloat for long

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Transportation - Traction

Pebbles and larger sediment are rolled along the sea bed

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Transportation - Longshore Drift

The process by which sediment is transported along a coastline. When waves approach the coastline at an angle the sediment will be carried up the beach at the same angle (SWASH) ; it then moves back down the beach at right angles (BACKWASH). The result is a zig zag motion along the beach which moves sediment along a coastline

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Coastal Deposition

Deptosition = when the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying.

Deposition happens when the swash is much stronger than the backwash (CONSTRUCTIVE WAVES)

Deposition is most likely to occur when:

  • Waves enter an area of shallow water
  • Waves entered a sheltered area e.g. bay or cove
  • There is little wind 
  • Good supply of material to carry 
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