2.2.1 Weathering

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Recognise that weathering involves the breakdown of rock in situ and, as such, should be distinguished from erosion.

Weathering is the breaking down of rocks in situ which means in their place of origin.  Erosion involves the movement of material to another place.

syllabus_link_buttonDescribe what is meant by different types of weathering – physical/mechanical (freeze-thaw action, exfoliation), chemical (carbonation, oxidation) and biological.

Types of Weathering

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Cambodia: biological weathering

Physical:  The breaking up of rocks by physical processes:

  • Freeze-thaw:  water enters cracks in rocks during the day & then freezes overnight. As it expands it cracks the rock.  This process repeats.
  • Exfoliation: Exposed rock in hot climates heats up and expands in the day & then cools and contracts at night. The outer layers heat & cool more quickly than inner layers & this cracks the rock.
  • Biological:  Tree roots penetrate cracks in rocks & force them to widen & crack.

 

Chemical: Rocks such as limestone are slowly dissolved by acid in rain & rivers.

syllabus_link_buttonExplain the main factors influencing the type and rate of weathering – climate and rock features (mineral composition, grain size of the rock, presence of lines of weakness). The influence of climate on the rate of weathering could be illustrated with reference to simple explanation as to why weathering is more rapid in humid tropical regions of the world than in temperate regions.