Weathering processes

 Topic 5: weathering

Name and describe types of weathering 

Physical/mechanical weathering

a) Exfoliation

• It’s a result of temperature differences e.g. in hot desert regions where it’s very hot during day and very cold at night

• The constant heating and cooling of rocks cause them to expand (day) and contract at night

• This put the top of the rock under stress and crack appear

• Eventually the outer layer of rock peel away forming a dome (exfoliation dome).

• This process is called exfoliation

b) Frost shattering/Freeze-thaw action

• Water may fill cracks in the rock.

• At night water freezes and expands

• During the day the ice thaws or melts

• The constant freeze-thaw action deepens and widens cracks and shatter the rock.

• The rock fragments are moved down the slope to form scree

Chemical weathering

• Chemical weathering is the result of rock undergoing a chemical change.

• It’s most rapid in moist, warm region where rocks have already been broken up by physical weathering.

(a) Oxidation

Oxygen from the atmosphere oxidises mineral e. g. iron can be oxdised to red iron oxide

(b) Carbonation

• common in limestone and chalk areas

• Rainwater combines with CO₂ to form a weak acid which weathers rocks away.

• CO2 in the atmosphere is dissolved by rain water to form a weak carbonic acid.

• The acid reacts with calcium carbonate to form calcium bicarbonate which is soluble.

• This solution causes joints to widen and deepen cracks called grykes separated by flat pavements called clints.

• Water can penetrate deeper along joints and form underground caves.

Biological Weathering

Caused by the action of animals and plants

• Animals

Burrowing animals e.g.. Earthworms dig holes, which brings soil deep down to the surface where it becomes exposed to weathering

• Plants

Roots of plants grow into cracks in rocks, as roots get bigger they force cracks to widen and rocks to breakdown.

Plants also secrete a weak acid that can cause rocks to dissolve

(Plant roots penetrating into the rock)

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