L3 Glaciation Processes


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L3 Glaciation Processes

  1. 1. Glacial Processes Key idea: ice is a powerful force in shaping the land as a result of weathering, erosion, transport and deposition
  2. 2. Objectives <ul><li>To be able to explain the following glacial processes: </li></ul><ul><li>Freeze thaw weathering </li></ul><ul><li>Processes of erosion - plucking and abrasion </li></ul><ul><li>Processes of movement and transportation – rotational slip and bulldozing </li></ul><ul><li>Deposition and the reasons for it </li></ul>
  3. 3. Freeze thaw weathering Freeze-thaw is when meltwater or rain gets into cracks in the bed rock, usually the backwall. At night the water freezes, expands and causes the crack to get larger. Eventually the rock will break away
  4. 4. Erosion – where rocks are broken down and moved away by ice eg. plucking + abrasion. Weathering - where rocks are broken down ‘in situ’ but are not moved away by ice, water or wind. eg. frost shattering. What is the difference between erosion and weathering ?
  5. 5. Glacial Erosion <ul><li>There are two main types of glacial erosion – plucking and abrasion </li></ul><ul><li>Plucking is the tearing away of blocks of rocks as a glacier moves. These blocks of rock had been frozen to the bottom of the glacier where water had entered joints in the rock and become frozen. When the ice moves downhill, rock is plucked from the back wall. </li></ul>
  6. 6. Abrasion is when rock fragments which have frozen to the base and the back of the glacier scrape the bed rock as the ice moves. Smaller rock particles have a sandpaper effect on the rocks over which the ice passes while the sharp edges of large rocks make deep grooves called striations
  7. 7. Direction of flow Crevasses
  8. 8. Tasks ( use textbook NT page 128) <ul><li>1. Draw labelled diagrams to show how each of the following processes operates: </li></ul><ul><ul><ul><li>Freeze thaw weathering </li></ul></ul></ul><ul><ul><ul><li>Plucking </li></ul></ul></ul><ul><ul><ul><li>Abrasion </li></ul></ul></ul><ul><li>2. Explain why the breakdown and removal of rock is quicker when </li></ul><ul><ul><ul><li>all three processes operate in the same area </li></ul></ul></ul><ul><ul><ul><li>Rocks have many lines of weakness </li></ul></ul></ul>
  9. 9. Glacial movement <ul><li>Melting ice in summer produces meltwater </li></ul><ul><li>This water helps to lubricate the underside of the glacier enabling it to slide downhill = basal slip. </li></ul><ul><li>In hollows this movement may be more curved = rotational slip </li></ul><ul><li>In winter when the glacier is frozen to the rocky surface the sheer weight of the ice and the influence of gravity cause individual ice crystals to deform in a plastic manner = internal deformation also causes the glacier to move downhill </li></ul>
  10. 11. Processes of transportation and deposition <ul><li>Moraine is angular rock material which is transported and later deposited by a glacier. </li></ul><ul><li>It is deposited when there is a rise in temperature. </li></ul><ul><li>As the glacier begins to melt it cannot carry as much material </li></ul>
  11. 12. Glacial Deposition <ul><li>Most deposition occurs when the ice melts. </li></ul><ul><li>As most melting occurs at the snout this is where most deposition occurs </li></ul><ul><li>Renewed advance of the glacier pushes the debris further downhill like a bulldozer – this process is bulldozing </li></ul>
  12. 13. Terms <ul><li>Freeze thaw </li></ul><ul><li>Plucking </li></ul><ul><li>Abrasion </li></ul><ul><li>Rock flour </li></ul><ul><li>Moraine </li></ul><ul><li>Lateral moraine </li></ul><ul><li>Medial moraine </li></ul><ul><li>Terminal moraine </li></ul><ul><li>Ground moraine </li></ul><ul><li>Rotational slip </li></ul><ul><li>Bulldozing </li></ul><ul><li>Scree </li></ul><ul><li>Striations </li></ul>
  13. 15. Bingo <ul><li>Choose 5 words </li></ul><ul><li>Abrasion Plucking Accumulation </li></ul><ul><li>Ablation Snout Glacier budget </li></ul><ul><li>Evaporation Ice sheet Valley Glacier </li></ul><ul><li>Weathering (freeze-thaw) Striation </li></ul><ul><li> </li></ul>