weathering

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MECHANICAL

- chemical composition is not changed.

freeze thaw

1) water fills a crack or joint from rainwater

2) water freezes and expands by 9% because of freezing temperatures. Crack widens.

3) repeated freeze thaw action increases size of crack when water melts at warmer temps.

4)loose blocks of rock are left near the rock called scree.

exfoliation

1) outer layer of rock is heated by the sun during the day so that it expands. Expansion produces cracks parallel to surface.

2) as temperatures drop in the night, the rock contracts. Contraction produces cracks at right angles to the surface.

3)repeated process leads to outer layers peeling away leaving behind rounded rocks and shaped outcrops.

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CHEMICAL

changes chemical composition of the rock

Solution

deposits of rock salt will dissolve in rainwater (like sugar dissolves in tea)

Carbonation

1) rainwater mixes with carbon dioxide in the air to form a weak carbonic acid.

2)acid reacts with rocks containing calcium carbonate eg limestone and chalk.

3) limestone is slowly dissolved and removed in solution by running water.

CACO3 + H2O +CO2 ----------> CA(HCO3)2

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BIOLOGICAL

breakdown of rocks by living things

1) plant roots grow into cracks on their surface and push them apart.

2) burrowing animals can loosen rock material

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