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Rocks and weathering

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This document defines and describes the three main types of weathering: physical, chemical, and biological. Physical weathering breaks rocks into smaller pieces through temperature changes and water, such as exfoliation weathering caused by hot temperatures and freeze-thaw weathering caused by melting and freezing water. Chemical weathering occurs as acid in rainwater reacts with minerals in rocks, either slowly over time from carbonic acid or more rapidly from acid rain. Biological weathering results from plants and animals breaking rocks into fragments.

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weathering • Describe what chemical and physical weathering can do • Investigate how different rocks are affected by weathering 1 of 42 © Boardworks Ltd 2008
What is weathering? Rocks are different shapes and sizes because they are changed by the conditions in their environment. The breakdown of rocks into smaller fragments is called weathering. Eventually the fragments become soil. Can you think of anything that could cause weathering? Rocks can be weathered by temperature change, water, frost and even plants and animals. 2 of 42 © Boardworks Ltd 2008
Types of weathering Which type of weathering is caused by each of these: temperature change acid rain plants and animals? There are three types of weathering: physical weathering biological weathering chemical weathering. 3 of 42 © Boardworks Ltd 2008
© 4 of 42 Boardworks Ltd 2008
Physical weathering Physical weathering occurs when rock is broken down into smaller pieces by the effects of temperature and water. Exfoliation weathering (or ‘onion-skin’ weathering) is caused by very hot weather. Freeze-thaw weathering is caused by the melting and freezing of water. Exfoliation and freeze-thaw weathering tend to occur in very different types of landscapes. Which type of weathering do you think will primarily occur in the desert, and which will occur in the mountains? 5 of 42 © Boardworks Ltd 2008
Exfoliation weathering in action 6 of 42 © Boardworks Ltd 2008
Freeze-thaw weathering in action 7 of 42 © Boardworks Ltd 2008
How can freezing water cause damage? You can see freeze-thaw weathering in action if you leave a bottle full of water in the freezer for too long. The water inside the bottle expands as it freezes. The ice that is formed creates huge forces on the bottle, which then cause it to break! Because water expands as it freezes it can create immense pressure in confined spaces. Does this explain why water pipes often burst in winter? 8 of 42 © Boardworks Ltd 2008
© 9 of 42 Boardworks Ltd 2008
Plants and weathering in action 10 of 42 © Boardworks Ltd 2008
What is chemical weathering? Slow chemical weathering Rainwater is naturally a weak acid because carbon dioxide in the air reacts with rainwater to form carbonic acid. This weakly acidic rain reacts with minerals in rocks and slowly wears them away. Rapid chemical weathering The burning of fossil fuels produces oxides of sulphur and nitrogen, which make rainwater more acidic. Acid rain reacts quickly with minerals, so the rocks get weathered more rapidly. 11 of 42 © Boardworks Ltd 2008
Examples of chemical weathering How has chemical weathering affected these rocks? 12 of 42 © Boardworks Ltd 2008
Which type of weathering? 13 of 42 © Boardworks Ltd 2008
• Test the different rocks to see how they are affected by weathering. 14 of 42 © Boardworks Ltd 2008

More Related Content

Rocks and weathering

  • 1. weathering • Describe what chemical and physical weathering can do • Investigate how different rocks are affected by weathering 1 of 42 © Boardworks Ltd 2008
  • 2. What is weathering? Rocks are different shapes and sizes because they are changed by the conditions in their environment. The breakdown of rocks into smaller fragments is called weathering. Eventually the fragments become soil. Can you think of anything that could cause weathering? Rocks can be weathered by temperature change, water, frost and even plants and animals. 2 of 42 © Boardworks Ltd 2008
  • 3. Types of weathering Which type of weathering is caused by each of these: temperature change acid rain plants and animals? There are three types of weathering: physical weathering biological weathering chemical weathering. 3 of 42 © Boardworks Ltd 2008
  • 4. © 4 of 42 Boardworks Ltd 2008
  • 5. Physical weathering Physical weathering occurs when rock is broken down into smaller pieces by the effects of temperature and water. Exfoliation weathering (or ‘onion-skin’ weathering) is caused by very hot weather. Freeze-thaw weathering is caused by the melting and freezing of water. Exfoliation and freeze-thaw weathering tend to occur in very different types of landscapes. Which type of weathering do you think will primarily occur in the desert, and which will occur in the mountains? 5 of 42 © Boardworks Ltd 2008
  • 6. Exfoliation weathering in action 6 of 42 © Boardworks Ltd 2008
  • 7. Freeze-thaw weathering in action 7 of 42 © Boardworks Ltd 2008
  • 8. How can freezing water cause damage? You can see freeze-thaw weathering in action if you leave a bottle full of water in the freezer for too long. The water inside the bottle expands as it freezes. The ice that is formed creates huge forces on the bottle, which then cause it to break! Because water expands as it freezes it can create immense pressure in confined spaces. Does this explain why water pipes often burst in winter? 8 of 42 © Boardworks Ltd 2008
  • 9. © 9 of 42 Boardworks Ltd 2008
  • 10. Plants and weathering in action 10 of 42 © Boardworks Ltd 2008
  • 11. What is chemical weathering? Slow chemical weathering Rainwater is naturally a weak acid because carbon dioxide in the air reacts with rainwater to form carbonic acid. This weakly acidic rain reacts with minerals in rocks and slowly wears them away. Rapid chemical weathering The burning of fossil fuels produces oxides of sulphur and nitrogen, which make rainwater more acidic. Acid rain reacts quickly with minerals, so the rocks get weathered more rapidly. 11 of 42 © Boardworks Ltd 2008
  • 12. Examples of chemical weathering How has chemical weathering affected these rocks? 12 of 42 © Boardworks Ltd 2008
  • 13. Which type of weathering? 13 of 42 © Boardworks Ltd 2008
  • 14. • Test the different rocks to see how they are affected by weathering. 14 of 42 © Boardworks Ltd 2008

Editor's Notes

  1. Photo credit: © 2008 Jupiterimages Corporation
  2. Photo credit (top right): Filipa Allen Photo credit (bottom left): Benjamin Earwicker
  3. Rocks and Weathering Worksheet 1 accompanies this slide.