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    Glaciers Glaciers Presentation Transcript

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