Weathering

• chemical - carbonation

  • CO2 dissolves in rain -> acid rain
  • calcium carbonate in limestone reacts with it to form calcium bicarbonate
  • this is soluble and washed away by percolating water, so limestone is removed
• chemical - hydrolysis

  • new solution formed as chemicals in rocks interact with water
  • E.g. water + granite -> feldspar crystals in granites, react chemically forming clay minerals
• chemical - hydration

  • certain minerals absorb more water, allowing them to expand causing stresses
  • E.g. clay
• physical - freeze-thaw
• physical - freeze-thaw

  water collects in cracks and freezes and expands by 10%. exerting pressure so cracks forced open. rock parts break free and water penetrates further
• physical - exfoliation 


  rock heats via conduction (only outer layers as they're poor conductors). at night layers cool and contract faster than inner layers, causing stresses and outer layers flake off
• physical - salt crystallisation 


  saline solution evaporates leaving crystals. temperature rises, salt expands exerting pressure causing disintegration
• physical - dilatation (pressure release)


  when rocks that are under great amount of pressure (e.g. igneous rocks like granite ) no longer have to bear a heavy loa, causing expansion and fracturing
• physical - vegetation root action
• factors affecting weathering

  • climate - Van Hoff's law - chemical increase 2-3x for every 10.C increase
  • human activity - chemical pollutants, acid rain, vegetation removal
  • rock type - e.g. limestone is susceptible to carbonation
  • rock structure - larger grain = higher surface area. natural lines of weakness allow water to penetrate further. porosity and permeability
  • vegetation - roots increase biological
  • relief - too steep water will run straight off. higher altitude - colder - freeze thaw