A) Mechanical / Physical weathering: Never in isolation Granular disintegration.
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Transcript of A) Mechanical / Physical weathering: Never in isolation Granular disintegration.
A) Mechanical / Physical weathering:
• Never in isolation
• Granular disintegration
• Frost shattering:
Insolationweathering:
Wetting and drying (slaking):
Exfoliation (spheroidal weathering):
• Salt crystal growth:
• pressure release - dilation
Organic action:
B) Chemical Weathering:
• decomposition of minerals so the chemistry of the rock is altered.
• H2O + CO2 <=> H2CO3
• Best in warm, humid conditions
Hydrolysis:
• H+ ions in water react to give clays.
• Rocks containing feldspar are particularly vulnerable (eg granite)
Hydration:
• the absorption of water into the crystal structure can weaken the rock
• Also a physical process (brown flakes)
Carbonation:
• H2CO3 + CaCO3 <=> Ca (HCO3)2
• Calcium hydrogen carbonate (or calcium bicarbonate) is very soluble in water and so the limestone dissolves
Solution:
• Some rocks simply dissolve eg halite (rock salt)
Oxidation:
• Minerals react with oxygen to form oxides or hydroxides
• eg ‘rusting’, where iron in ferrous form is oxidised into its ferric form
• Humic (organic) acid from decaying flora & fauna attack certain minerals• Lichens extract iron
Chelation:
Rates of weathering depend on:
• Rock type: quartz is unaffected by solution, hydrolysis and oxidation
(sand on a beach)
Rock structure(joints):
Climate:
• A temperature ‘range’
• Water
• Vegetation