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Physical weathering
Rocks gradually wear away. This is called weathering. There are three types of weathering:
- physical weathering
- chemical weathering
- biological weathering
Remember, when you answer questions about weathering, mention what is causing the weathering and what it does to the rock.
This page is about physical weathering - which is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.
Temperature changes
When a rock gets hot it expands a little, and when a rock gets cold it contracts a little. If a rock is heated and cooled many times, cracks form and pieces of rock fall away. This type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night.
Freeze-thaw
Water expands slightly when it freezes into ice. This is why water pipes sometimes burst in the winter. You might have seen a demonstration of this sort of thing at school - a jar filled to the brim with water eventually shatters after it is put into a freezer.
The formation of ice can also break rocks. If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apart. When the ice melts later, water can get further into the crack. When the rock freezes again, it expands and makes the crack even bigger. This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
Freeze-thaw weathering
Wind, rain and waves
The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. The rain can lash against a rock and wear it away. Waves can crash against a rock and wear it away.
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