weathering + erosion

• solution - chemical reaction between seawater (has weak acid) and susceptible rocks like limestone
• attrition - pieces of bedload hit against one another , they break apart , become smaller and more rounded
• hydraulic action - breakdown of cliffs due to force of water being compressed into cracks of rocks. repeated action of water forced in and out of cracks in rocks leads to breakdown of surrounding cliff
• cavitation - air bubbles trapped in water are compressed into small spaces. happens whne waves hit cliff and air bubbles are forced into cracks in the rock face.
• types of weathering:

  • biological
  • chemical
  • mechanical (physical)
• biological weathering is when rocks are broken by living things e.g plants and animals e.g Algae = breakdown of rocks from releases of chemicals
• chemical weathering is the changing of chemical composition e.g carbonation weathering
• mechanical weathering is physical , NO changing of rocks chemical composition
• abrasion - pieces of rocks picked up by waves and hit against bed , beach or cliffs. wears them away over time
• examples of chemical weathering:

  • carbonation
  • oxidation
• marine processes of erosion:

  • cavitation
  • quarrying
  • solution
• types of physical weathering:

  • wetting drying
  • exfoliation
  • crystalisation
  • freeze-thaw
• cavitation is the opening up of cavaties within cliffs due to changes in pressure as waves crash into and out of cracks in rocks.
• quarrying - destructive waves in storm conditions plunge heavy hydraulic pressure on cliff faces , vibration of cliff dislodges bits of rock and undercuts base of cliff
• swash aligned beaches - waves come in directly to coast
• processes of erosion:

  • abrasion
  • attrition
  • hydraulic action
  • cavitation
  • solution
  • suspension
• traction : heavy sediment rolls along seabed , pushed by currents
• saltation : smaller sediment bounces along seabed
• suspension : small sediment carried within flow of water
• solution : dissolved material carried within water
• wetting and drying

  frequent cycles of wetting and drying and common on the coast

  • rocks rich in clay (such as shale) expand whne they get wet and contract as they dry
  • causes them to crack and break up
• what causes freeze-thaw weathering to occur?

  water enters a crack or joint in the rock when it rains and then freezes in cold weather.

  • when water freezes , expands in volume by 10%.
  • puts pressure on rock , forces crack to widen
• what is freeze-thaw weathering?

  repeated freezing and thawing , fragments of rock break away and collect at base of cliff as scree

  • angular rock fragments used by sea as tools in marine erosion
• what is oxidation?

  reaction of rock minerals with oxygen

  • iron reacts with oxygen to form a rust red powder which leaves rock more vulnerable to weathering
• how do birds and animals cause biological weathering?

  puffins and rabbits dig burrows into cliffs
• how do marine organisms cause biological weathering?

  piddocks burrow into rocks and can secret acids such as limpets