Glaciers

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Glaciers

  1. 2. <ul><li>1. Glacier </li></ul><ul><li>A thick ice mass that forms over hundreds or thousands of years </li></ul><ul><li>Cover nearly 10% of Earth’s land area </li></ul><ul><li>Form in regions where more snow falls each winter than melts in the summer </li></ul><ul><li>Flow downhill </li></ul><ul><li>Agents of erosion and important part of the rock cycle </li></ul>
  2. 3. <ul><li>Valley glaciers – ice masses that slowly advance down valleys that were originally occupied by streams </li></ul>
  3. 4. <ul><li>Ice sheets – enormous ice masses that flow in all directions from one or more centers and cover everything </li></ul><ul><li>Greenland – 80% is covered with ice </li></ul><ul><li>Antarctica – the glacier is nearly 4300 m thick, accounts for 80% of the world’s ice and holds nearly 2/3 of the world’s fresh water. </li></ul>
  4. 6. <ul><li>2. Movement of Glaciers </li></ul><ul><li>Plastic flow – pressure causes the brittle ice to distort and change. The ice flows. </li></ul><ul><li>Basal slip – the entire ice sheet slips and slides downhill in response to gravity </li></ul><ul><li>Above the snowline, a glacier forms where more snow falls in winter than melts in summer. This is called the zone of accumulation. </li></ul><ul><li>In the zone of wastage the glacier loses ice to melting. </li></ul><ul><li>Glaciers also lose ice in a process called calving. This produces icebergs. Only 10% of the iceberg is visible. </li></ul>
  5. 8. <ul><li>3. Glacial erosion </li></ul><ul><li>Plucking – blocks of rock are frozen in the ice and flow with the glacier. </li></ul><ul><li>Abrasion – the glacier slides on the bedrock smoothing and polishing the surface </li></ul><ul><li>The pulverized rock is as fine as flour and the meltwater leaving the glacier has a milky consistence. </li></ul>
  6. 10. <ul><li>4. Glacial Landforms </li></ul><ul><li>Glacial trough – U shaped valley </li></ul>
  7. 11. <ul><li>Hanging valleys – some side valleys are left higher when the glacier retreats and this produces spectacular water falls </li></ul>
  8. 12. <ul><li>Cirques – bowl-shaped depressions at the head of the glacier </li></ul><ul><li>Aretes – saw-toothed ridges </li></ul>
  9. 13. <ul><li>Horns – sharp pyramid shaped peaks </li></ul>
  10. 14. <ul><li>5. Glacial drift </li></ul><ul><li>Till – sediments deposited directly by glaciers, unsorted </li></ul><ul><li>Stratified drift – sediment laid down by glacial meltwater, sand and gravel </li></ul><ul><li>Glacial erratics – large boulders found lying on the ground (different material than bedrock) </li></ul>
  11. 16. <ul><li>6. Moraines – when glaciers melt layers or ridges of till are left </li></ul><ul><li>Lateral moraine – ridges of till that form along the side of glacial valleys </li></ul><ul><li>End moraines – deposits of till that forms at the end of the glacier </li></ul><ul><li>Ground moraines – the glacier deposits sediment as the ice melts, fills in low spots and clogs old stream channels resulting in poorly drained swamp lands </li></ul><ul><li>Terminal and recessional moraines – end moraines formed during stationary periods of glacial advance or retreat </li></ul>
  12. 17. <ul><li>7. Other Glacial Depositional Features </li></ul><ul><li>Outwash plains – streams emerging from the glacier slow and drop sediment </li></ul>
  13. 18. <ul><li>Kettles – form when buried blocks of ice melt </li></ul>
  14. 19. <ul><li>Drumlins – streamlined hills of stratified drift, the steep side faces the direction the ice came from </li></ul>
  15. 20. <ul><li>Eskers – snake-like ridges of composed of sand and gravel that were deposited by streams once flowing in tunnels beneath glaciers </li></ul>
  16. 21. <ul><li>8. Glacial Ice Ages </li></ul><ul><li>In the most recent ice age, glaciers covered about 30% of the Earth </li></ul><ul><li>Pleistocene epoch </li></ul>
  17. 22. <ul><li>9. Impact on Drainage </li></ul><ul><li>Formation of the Great Lakes </li></ul><ul><li>Basin and Range region of Utah and Nevada was once filled with a large lake – Lake Bonneville . The Great Salt lake is remnants of that glacial lake. </li></ul>

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