Weathering Processes What are the processes of weathering

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Weathering Processes What are the processes of weathering and how do they affect rocks?

Weathering Processes What are the processes of weathering and how do they affect rocks?

WEATHERING Processes of weathering are those that break down rocks “in situ” (where they

WEATHERING Processes of weathering are those that break down rocks “in situ” (where they are found), on or near the earth’s surface. This is done in two ways: physical disintegration (breaking them down into smaller particles) and chemical decomposition (e. g. natural acids dissolving the rocks away).

DIFFERENT TYPES OF WEATHERING Physical (or mechanical) weathering: when repeated physical stresses and strains

DIFFERENT TYPES OF WEATHERING Physical (or mechanical) weathering: when repeated physical stresses and strains cause rocks to break down into smaller particles: 1. Freeze-thaw (or frost shattering) – this is very common in highland locations where daytime temperatures are above freezing but those at night drop below freezing. Rainwater trapped in cracks in surface rocks, freezes and expands (by 9%). This puts stress on the cracks and repeated cycles of freezing and thawing will eventually cause the rock to break into smaller particles.

2. Heating and cooling (onion-skin weathering)– this is very common in 1. desert locations

2. Heating and cooling (onion-skin weathering)– this is very common in 1. desert locations where there is a large diurnal (24 hour) temperature range (maybe 35 C during the day and 5 C at night). The daytime heat causes the surface layers of rocks to expand at night when the temperatures drop, they contract. These repeated cycles of expansion and contraction, cause the surface layers to crack and fall away.

Chemical weathering – when natural acids (e. g. “acid rain” or the biotic acids

Chemical weathering – when natural acids (e. g. “acid rain” or the biotic acids released as vegetation decomposes), dissolve away soluble rocks (e. g. Limestone). As chemical reactions occur more quickly in warm and humid conditions, this type of weathering is common in the world´s tropical rainforest regions. Typically carbon dioxide in the atmosphere will mix with water vapour to form a weak carbonic acid (commonly called “acid rain”). This falls on and dissolves soluble rocks like limestone – a type of weathering known as solution weathering.

Biological weathering Plants and animals breaking down rocks: - Roots growing in cracks to

Biological weathering Plants and animals breaking down rocks: - Roots growing in cracks to split them apart; - Organic acids released during decomposition - Animals burrowing into and weakening rocks

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