Weathering
Geography: KS3, topic 2.1.4
Weathering
Weathering and erosion constantly attack rocks. Weaker rocks are weathered faster than harder, stronger, more resistant rocks.
Biological weathering
- Biological weathering happens when plants or animals break down rocks.
- For example, trees roots can grow into cracks in rocks and split the rocks apart as the roots grow.
- Animals can wear rocks down as they burrow into cavities.
Chemical weathering
- In chemical weathering, the chemical composition of rock changes.
- When the climate is warm and wet, carbonic dioxide can dissolve in rain to create a 'carbonic acid'.
- The carbonic acid in rainfall hits rocks and dissolves the parts of the rock made of calcium carbonate.
Freeze-thaw weathering
- Water expands when it freezes.
- When water fills cracks in rocks, if it then freezes, it expands, putting pressure on the rock.
- The water will then melt, but it has put pressure on the rock.
- Eventually, this process of freezing and thawing will wear down the rock until it cracks.
Onion-skin weathering
- Onion-skin weathering is when the outer layer separates from the rock.
- One form of this weathering is exfoliation, where the outer layer of the rock is peeled off by the weather.
Onion-skin weathering cont.
- Rocks expand during the day in very hot temperatures and then contract again in the cooler night-time temperatures.
- This constant movement over thousands of years finally causes the outer layer to peel away.
- The process then repeats with the next layer.
Test yourself on Weathering
Which type of weathering is caused by tree roots widening cracks in rocks?
How does onion-skin weathering occur?