Coastal Mass Movement


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  • Water is not a lubricant. This statement confuses me. Could you please explain? Your statement seems to suggest that water is the catalyst for the 'lubrication' that you mention and even if not (in this case) is water not a lubricant in other circumstances?
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Coastal Mass Movement

  1. 1. Coastal Mass Movement (Landslides) Higher Geography Lithosphere
  2. 2. Introduction <ul><li>Mass movement occurs when weathered material moves downhill under the force of gravity (often lubricated by water). </li></ul><ul><li>Landslips in coastal areas occur because of erosion from the waves, physical (freeze-thaw) and chemical (solution) weathering. </li></ul>
  3. 4. A classification of mass movement After Carson and Kirkby
  4. 5. 4 star hotel in Scarborough, North Yorkshire (1993).
  5. 7. Black Ven, Dorset Coast
  6. 8. Black Ven, Dorset Coast
  7. 9. Osmington Coastal Path, Dorset Coast
  8. 10. How Landslips work (1) <ul><li>Rain water sinks through the porous rocks but once it reaches the underlying clays it can sink no further. The water builds up along the junction between the rock layers and seeps out of the cliffs as a series of springs. </li></ul><ul><li>After periods of prolonged rainfall, the build up of water increases the weight of the cliff top. Increased poor pressure reduces the friction and allows large sections of the cliff top to break away. </li></ul>
  9. 11. How Landslips work (2) <ul><li>As the cliff top block subsides, it rotates along the slip plane within the cliff, resulting in the flat surface tipping back towards the cliff. </li></ul><ul><li>The main type of landslide that occurs at the coast is called slumping . </li></ul>
  10. 12. Slumping (also landslips) Slumps occur in weaker rocks and involve some rotational movement. Slumping can occur after heavy rainfall or earthquakes Back tilted slopes Large blocks break away Sliding surface is concave Soft boulder clay cliffs can be undercut by the sea and slumps are common.
  11. 13. Landslides in Dorset <ul><li>The Dorset and East Devon coast contains a wide range of landslides, both large and small. </li></ul><ul><li>The coast is unstable because there are numerous situations where porous strata (eg: chalk and sandstone) lie over impermeable clays. </li></ul>
  12. 14. Old Harry Rocks
  13. 15. Another view Sliding surface is concave Clay Sandstone
  14. 16. Impermeable Clay Permeable Sandstone Rotational Slumping Sheer Face
  15. 19. Your turn <ul><li>Make notes on Landslides and slumps from page 87. </li></ul><ul><li>Copy Rotational sliding diagram from page 88. </li></ul>Copy Fig 4.13 from page 87.