Weathering

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The different types of weathering. How and why they happen.

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Weathering

  1. 1. <ul><ul><li>&quot;We live on an island surrounded by the sea. The coastline looks very different around the UK and is continually shaped by the sea.&quot; </li></ul></ul>
  2. 2. Don’t have a cow, man! Here’s what w e a re l earning t oday! <ul><li>An introduction into how coastlines change. </li></ul><ul><li>What is weathering? </li></ul><ul><li>What are the different types of weathering? </li></ul>Apart from my brain, this is w hat I ’m l ooking f or! <ul><li>An explanation of what is mechanical, biological and chemical weathering. </li></ul><ul><li>One example of each type of weathering. </li></ul>
  3. 3. Happisburgh, North Norfolk Write down 5 geographical questions you could ask someone about this scene. (5 mins) Why? Where? What? How? Who?
  4. 4. Landscape The different landscapes of the earth’s surface are the combined result of internal and external forces. What are the internal forces ? What are the external forces ? w - - t - - - - n - e - - s - - -
  5. 5. Landscape The different landscapes of the earth’s surface are the combined result of internal and external forces. Internal forces. The work of Plate Tectonics. This results in the formation of volcanoes and fold mountains, and the occurrence of earthquakes, and continental drift External Forces. Weathering and erosion. These two forces are known are often termed “Earth Sculpture”
  6. 6. Earth Sculpture Whenever rocks are exposed at the surface of the earth they are acted upon by external forces. . <ul><li>There are 2 different external processes: </li></ul><ul><li>Weathering. </li></ul><ul><li>Erosion. </li></ul>What is this ? What is this ?
  7. 7. Earth Sculpture Whenever rocks are exposed at the surface of the earth they are acted upon by external forces. . <ul><li>There are 2 different external processes: </li></ul><ul><li>Weathering. </li></ul><ul><li>Erosion. </li></ul>The breakdown of rocks in situ*. The further destruction, transport and deposition of the weathered rock material.
  8. 8. Weathering. The breaking up of rocks in situ. What processes do you think can break up rock?
  9. 9. Weathering. The breaking up of rocks in situ. There are 3 main types of weathering: Mechanical or Physical . This is when exposed rocks get broken up by a physical force. Chemical. Biological. This is when exposed rocks get broken up by something living. 1. 2. 3. This is when exposed rocks break up due to a chemical reaction.
  10. 10. Physical or Mechanical Weathering. This is caused by : <ul><ul><li>1. High Temperatures. </li></ul></ul><ul><ul><li>2. Low Temperatures. </li></ul></ul>
  11. 11. Physical or Mechanical Weathering. <ul><ul><li>1. High Temperatures. </li></ul></ul>This results in exfoliation . (Also known as onionisation or rock peeling ) During the Day During the Night The sun’s rays heat the surface of the rock. The outer layer of the rock expands and pulls away from the cooler interior. This causes a crack, parallel to the surface, to develop. Cool Interior The outer layer cools down rapidly as there is no sun. As it cools the rock contracts and cracks at right angles to the surface develop.
  12. 12. Eventually the outer layer breaks up into large chunks of rock . <ul><ul><li>1. High Temperatures. </li></ul></ul>These chunks then fall to the bottom of the hill under gravity. This results in exfoliation . (Also known as onionisation or rock peeling ) Physical or Mechanical Weathering. They form piles of rubble called scree..
  13. 13. Scree !
  14. 14. Physical or Mechanical Weathering. <ul><ul><li>2. Low Temperatures . </li></ul></ul>This results in frost shattering. (Also known as sapping or freeze-thaw ) Water fills a crack in a rock When the temperature falls to below 0 0 the water freezes. What happens to water when it freezes ? Eventually the rock shatters into several jagged pieces. When the temperature rises the ice melts and changes back to water. It expands by 10% of its volume, causing the crack to get wider.
  15. 15. Chemical Weathering. This is when certain chemicals in rocks are dissolved by the action of rainwater. <ul><ul><li>Ordinary rainwater contains small amounts of acid. </li></ul></ul>What kind of acid do you find in rain water ? Carbonic acid. When this acid comes into contact with certain rocks, (chalk and limestone) the acid reacts with the rock and causes it to rot and to crumble. Exposed rock Statues are also weathered in this way
  16. 16. Chemical Weathering. This is caused by the action of rain water. Spectacular scenery is created by this type of weathering in areas of limestone. Why? Limestone cliffs Dry valley Limestone Caves Limestone pavement
  17. 17. Biological Weathering. <ul><ul><li>Plants. </li></ul></ul>What might cause this type of weathering ? Seeds may fall into cracks in rocks where shelter and moisture help them grow into small plants or trees. As the tree grows the roots develop and force the crack to widen. <ul><ul><li>Animals. </li></ul></ul>Burrowing animals such as rabbits, moles and even earthworms can help to break down rocks. The rock eventually breaks up into lots of different pieces. <ul><li>This is when rocks are broken up by the actions of </li></ul><ul><ul><ul><ul><ul><li>1. Plants and </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>2. Animals </li></ul></ul></ul></ul></ul>
  18. 18. Weathering-Summary The breaking up of rocks in situ. What is weathering ? What are the 3 main types of weathering ? Mechanical or Physical . Chemical. Biological. Where would you be most likely to find rock-peeling? Where would you be most likely to find freeze-thaw? Where would you be most likely to find chemical weathering ? In areas where temperatures are high during the day and cold at night… hot deserts In areas where temperatures oscillate about freezing point.. high mountain areas. In areas where there is a lot of rain and there are rocks which contain calcium carbonate.
  19. 19. Activity 1 Write a sentence to describe what weathering means. Activity 2 Copy the set of diagrams below and annotate them to describe how mechanical freeze-thaw weathering occurs. <ul><li>The sentences below can be used to annotate the diagrams. But they are not in the right order! </li></ul><ul><li>The water expands when it freezes and makes the crack wider. </li></ul><ul><li>A crack in the rock fills with water. </li></ul><ul><li>Eventually the crack gets so wide that the rock splits. </li></ul>
  20. 20. <ul><li>Activity 3 </li></ul><ul><li>Draw your own set of annotated diagrams to describe how biological weathering occurs. </li></ul><ul><li>Activity 4 </li></ul><ul><li>Put these sentences in order to describe how chemical weathering occurs. </li></ul><ul><li>The weakly acidic rainwater attacks the rock. </li></ul><ul><li>Rainwater becomes acid as it falls through the atmosphere. </li></ul><ul><li>The rock dissolves and crumbles away. </li></ul><ul><li>Activity 5 </li></ul><ul><li>Carry out a survey of this school building to find out where the building is being weathered! </li></ul><ul><li>First of all, think of some enquiry questions you could ask about where the weathering is found, e.g. how high up or on which side of the building it is. </li></ul>
  21. 21. Time to go outside! If you have worked well and have left yourself enough time, it’s time to go outside to put your questions to the test! Lets go and find out if we can see weathering in action!
  22. 22. Do you have w hat I ’m l ooking f or? <ul><li>An explanation of what is mechanical, biological and chemical weathering. </li></ul><ul><li>Mechanical weathering –  </li></ul><ul><li>Biological weathering –  </li></ul><ul><li>Chemical weathering –  </li></ul><ul><li>One example of each type of weathering – using keywords. </li></ul><ul><li>Mechanical weathering –  </li></ul><ul><li>Biological weathering –  </li></ul><ul><li>Chemical weathering –  </li></ul>
  23. 23. Next lesson: EROSION!!! Slideshow adjusted by S.Rackley, original source unknown.

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