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A) Mechanical / Physical weathering:

A) Mechanical / Physical weathering:. Never in isolation Granular disintegration. Frost shattering:. Insolation weathering:. Wetting and drying (slaking):. Exfoliation (spheroidal weathering):. Salt crystal growth:.

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A) Mechanical / Physical weathering:

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  1. A) Mechanical / Physical weathering: • Never in isolation • Granular disintegration

  2. Frost shattering:

  3. Insolationweathering:

  4. Wetting and drying (slaking):

  5. Exfoliation (spheroidal weathering):

  6. Salt crystal growth:

  7. pressure release - dilation

  8. Organic action:

  9. B) Chemical Weathering: • decomposition of minerals so the chemistry of the rock is altered. • H2O + CO2 <=> H2CO3 • Best in warm, humid conditions

  10. Hydrolysis: • H+ ions in water react to give clays. • Rocks containing feldspar are particularly vulnerable (eg granite)

  11. Hydration: • the absorption of water into the crystal structure can weaken the rock • Also a physical process (brown flakes)

  12. Carbonation: • H2CO3 + CaCO3 <=> Ca (HCO3)2 • Calcium hydrogen carbonate (or calcium bicarbonate) is very soluble in water and so the limestone dissolves

  13. Solution: • Some rocks simply dissolve eg halite (rock salt)

  14. Oxidation: • Minerals react with oxygen to form oxides or hydroxides • eg ‘rusting’, where iron in ferrous form is oxidised into its ferric form

  15. Humic (organic) acid from decaying flora & fauna attack certain minerals • Lichens extract iron Chelation:

  16. Rates of weathering depend on: • Rock type:quartz is unaffected by solution, hydrolysis and oxidation (sand on a beach)

  17. Rock structure(joints):

  18. Climate: • A temperature ‘range’ • Water • Vegetation

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