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Weathering
- The breaking up of rocks and soil into smaller particles
- Weathered rock / broken rocks are not moved away. The smaller rocks are in a pile where
they were broken up from larger rock.
Physical: natural features that can be touched, seen or felt
Chemical: a substance that can react with another substance and change its shape, form or
composition e.g.: acid
Biological: anything connected with living plants and animals
Processes: a series of stages
Factors that cause weathering include: physical, chemical, biological and human activities
Physical weathering
- Happens when a physical force breaks rocks into smaller pieces e.g. frost shattering and
exfoliation
1. Frost shattering
- Frost shattering is caused by the constant freezing and thawing of water in the cracks of
rocks which causes pressure to make rocks split. It mostly occurs in mountainous areas
because temperatures are low.
Exfoliation
- The peeling off in layers
- The sun shines down on rocks, the surface of the rock heats up and expands [gets bigger-
the outer layer of the rock moves away from the rock]. At night the rock cools down and
contracts [gets smaller]. The constant expansion and contraction of the rock will cause the
surface to weaken. The edge of the rock becomes loose and breaks away in curved
shells/pieces
- Exfoliation happens in mostly desert, semi desert and continental regions where there is a
big temperature difference between day and night.
Chemical weathering
- Occurs when the chemical composition of certain rocks is changed.
1. Carbonation
- Rain water in the atmosphere mixes/dissolves with carbon dioxide [CO2] in the air to form a
weak acid [carbonic acid] which falls as acid rain. This carbonic acid changes calcium
carbonate in limestone into calcium bicarbonate. Calcium bicarbonate is soluble in water
thus allowing weathering to occur.
, 2. Oxidation
- Oxygen in the air mixes/dissolves in water and combines with chemicals in the rocks to form
oxides. If a rock contains a lot of iron then oxidation produces a brown material [iron oxide]
that looks like rust on the rock. Oxidation weakens rock and causes it to crumble.
- Organic acid – acid produced by dead plants and animals that eats at rocks.
- Caves are formed when lots of acidic water flows into the cracks and removes the limestone
- Water is necessary for chemical weathering as it combines with gases producing acids that
break down rocks.
- Chemical weathering occurs in regions that are hot and wet for most of the year.
Biological weathering
- Caused by the actions of plants and animals.
1. Plants
- Plants can grow on rocks because roots can grow down between cracks to look for water
and minerals in the rock.
- Cracks are widened as the roots grow into them.
- Roots eventually cause parts of rock to break off as they grow.
- This happens in all regions where trees have a strong root system.
- Small plants, fungi and lichen can grow in tiny cracks making them wider.
Fungi- organisms like mushroom that live on organic matter.
Lichen- type of fungus that lives on rock or places where there is no soil.
2. Animals
- Animal trails can cause weakness in rocks and stones that will allow for water and roots to
penetrate the rocks.
- Burrowing animals weaken rocks by forcing the cracks wider.
climates
type of climate temperature vegetation
tropical hot and wet thick forest vegetation
hot desert hot temperatures dry with little vegetation
during day and
summer, cold during
night and winter
tundra cold and icy little vegetation
cold in winter,
coniferous forest warm good rainfall and forest vegetation
in summer
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