1.1.5

• Freeze-thaw occurs when water gets into cracks in rocks and freezes. 

  This then expands by around 9%. 

  The repeated freeze-thaw action puts pressure on the rocks until they eventually crack and break the rock. 

  Freeze-thaw usually occurs when the temperature oscillates around freezing point. 

  As coastal climates tend to be milder this process is only really effective during very cold winters.
• Biological weathering

  -growing plant roots widen cracks as does the leverage created by bushes and trees swaying in strong winds. 

  -burrowing animals and nesting birds excavate material in partially weathered and eroded cliffs. 

  -seaweed attaches itself to rocks and the action of the sea can be enough to cause swaying to prise away loose rocks from the sea floor. 

  -Some organisms, algae for example, secrete chemicals capable of promoting solution.
• Chemical weathering 

  -Oxidation occurs when oxygen reacts with minerals such as calcium and magnesium to form iron oxide. Iron oxide is reddish brown in colour and causes the decomposition of rock.

  -Hydration occurs when water is absorbed by minerals in the rock, creating crystals which exert pressure on the surrounding rock, eventually causing it to crumble.
• chemical weathering:

  -Hydrolysis occurs when water reacts with minerals in the rock causing the chemical composition of the rock to change and become more unstable. This reaction makes the rock more susceptible to decomposition.

  -Carbonation -rainwater absorbs carbon dioxide from the air to form a weak carbonic acid. This reacts with calcium carbonate in rocks, such as limestone and chalk, to form calcium bicarbonate, which is easily dissolved. The cooler the temperature of the rainwater, the more carbon dioxide is absorbed (so carbonation is more effective in winter).
• chemical weathering

  -Solution (corrosion) occurs because many minerals are soluble and are removed when they come into contact with water
• Mass movement can happen suddenly or more slowly over a long period of time. 

  If the force of gravity on a slope exceeds the resisting forces of the slope it will fall and cause a landslide. 

  Factors such as heavy rain, erosion at the base, or changes to the strength of the material the slope is made of through weathering can all contribute to landslides.
• Marine erosion processes


  • Hydraulic action
  • Wave quarrying
  • Abrasion/corrasion
  • Attrition
  • Corrosion/solution
• Hydraulic action


  Breaking waves create hydraulic pressure in joints. Air in cracks in a cliff face can be compressed by the force of the waves and then rushes out when the wave retreats. This can weaken the rock.
• Wave quarrying


  High-energy waves can exert a force of many tonnes per metre squared, which can remove loose, unconsolidated rock fragments.
• Abrasion/corrasion


  Rock fragments wear away the coast. Abrasion involves rock particles being scraped over bare rock, wearing it away and smoothing it. Corrasion occurs when waves hurl debris against the rock, causing pieces to be broken off and wearing it away.
• Attrition


  Eroded rocks are worn smaller and rounder by constant rubbing against each other with the movement of the sea.
• Corrosion/solution


  Weak acidic sea water chemically attacks certain rocks, dissolving minerals.
• Mass movement processes


  • Landslide
  • Rockslide
  • Slump/mudslide
  • Rotational slip
  • Soil creep
  • Solifluction
• Landslide


  • Rapid speed
  • Rocks affected by physical weathering or marine erosion collapse downwards
• Rockslide


  • Rapid speed
  • Rocks slide down a cliff face when the bedding planes dip towards the sea
• Slump/mudslide


  • variable speed
  • Saturated soft rock (often on top of impermeable rock) flows downhill
• Rotational slip


  • Variable speed.
  • softer rocks give way moving downhill in one mass along a concave slip surface
• Soil creep


  • Slow speed
  • Soil particles move downslope, aided by rain drop impact
• Solifluction


  • Slow speed
  • Movement of wet soil downslope caused when underlying layers are frozen
• Cliff retreat and the formation of wave-cut platforms


  1. Marine erosion creates a wave-cut notch at the cliff base

  2. The cliff is undercut, collapses and the process repeats

  3. The cliff retreats, leaving a gently sloping surface (1-5°) called a wave-cut platform, also called an intertidal shore platform

  4. A wide wave-cut platform prevents marine erosion processes reaching the cliff foot except in storms or the highest tides, reducing the rate of erosion

  5. Sub-aerial processes continue working on the cliff face, reducing the angle of slope (Figure 1.6)