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L4 Glacial Troughs


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L4 Glacial Troughs

  1. 1. Glacial Erosion features - Glacial Valleys Objectives: To understand the formation of the following glacial erosion features: U – shaped valleys Hanging valleys To know the terms: truncated spurs, alluvial fan
  2. 2. Words… <ul><li>Weathering Erosion </li></ul><ul><li>Plucking Abrasion </li></ul><ul><li>Crevasse Arete </li></ul><ul><li>Pyramid peak Corrie </li></ul><ul><li>Tarn plucking </li></ul><ul><li>Striation moraine </li></ul><ul><li>Snout ablation </li></ul><ul><li>accumulation </li></ul>
  3. 3. Glacial features on an OS map
  4. 4. Pyramid Peak Arete Valley Glacier Corrie
  5. 5. Corrie Arête Pyramidal Peak
  6. 7. Types of Glaciers – Valley Glacier Tongas National Forest, Alaska
  7. 8. <ul><li>Glaciers most commonly flow along pre-existing river valleys. </li></ul><ul><li>They carve relatively straight courses </li></ul><ul><li>Their strength enables them to form the following features: </li></ul><ul><ul><li>Glacial troughs </li></ul></ul><ul><ul><li>Truncated spurs </li></ul></ul><ul><ul><li>Hanging valleys </li></ul></ul><ul><ul><li>Ribbon lakes </li></ul></ul>
  8. 9. U shaped Valleys
  9. 11. U-Shaped Valley in Tracy Wilderness, Southeastern Alaska
  10. 12. U-shaped valley formation
  11. 13. U shaped Valley <ul><li>When a glacier erodes its valley , a classic U shape is formed. </li></ul><ul><li>U shaped valleys often start life as river valleys that existed before glaciation occurred. </li></ul><ul><li>The glaciers then followed the existing V shaped valleys, eroding the interlocking spurs, straightening the valley sides and deepening the valley floors as the ice moved. </li></ul><ul><li>U shaped valleys are also known as glacial troughs. </li></ul><ul><li>The flat floor is roughly shaped by the ice which tends to cut down more evenly than flowing water. A thick layer of glacial debris (ground moraine) is deposited as the ice retreats, creating a well drained and fertile soil </li></ul>
  12. 15. U-shaped valley (trough) The Nant Ffrancon Valley The once u-shaped valley has been distorted by moraine deposits and a collection of scree from weathering and mass movement.
  13. 16. U shaped Valley Glacial U shaped valley with steep sides, flat floor, and truncated spurs (middle left)
  14. 18. Langdale – a U-shaped valley Steep valley sides Flat valley floor
  15. 19. <ul><li>What is this feature? </li></ul><ul><li>Look at how this valley appears to be suspended above the valley below </li></ul><ul><li>It is a hanging valley </li></ul><ul><li>How is it created? </li></ul>
  16. 20. Hanging Valley A HANGING VALLEY is a glacial valley that runs above and perpendicular to another glacial valley
  17. 21. Hanging Valley
  18. 23. Receding tributary glacier Medial moraines Former height of glacier Main valley glacier Hanging valley Truncated spur U shaped valley ‘ Misfit’ stream Waterfall Corrie Pyramid peak Truncated spur
  19. 24. On an O.S. map
  20. 26. Can you identify a corrie, pyramid peak, hanging valley, terminal moraine, corrie lip, arete, glacial trough? In summary….
  21. 27. Glacial Landscapes <ul><li>1 is a Pyramidal Peak because it has steep, triangular faces divided by sharp ridges or arêtes. </li></ul><ul><li>2 is an Arête , because it is a sharp ridge between corries. </li></ul><ul><li>3 is a Corrie or Cirque , because it is an armchair shaped hollow with steep back and sides. </li></ul><ul><li>4 is a Corrie Lochan or Tarn , because water has gathered in the hollow in the floor of the corrie. </li></ul><ul><li>5 is an Alluvial Fan , because it is a fan shaped pile of rock remains (alluvium) washed down by the stream and piled up where the steep valley side meets the valley floor. </li></ul><ul><li>6 is a Ribbon Lake , because it is a long narrow lake in a part of the valley cut deeper by the glacier. </li></ul><ul><li>7 is a Truncated Spur , because the ridge has been cut off sharply by the ice that flowed down the main valley. </li></ul><ul><li>8 is a Misfit Stream , because it is far too small to have cut the valley. </li></ul><ul><li>9 is a Hanging Valley , because the valley floor is much higher than the floor of the main valley. </li></ul><ul><li>10 is a 'U' Shaped Valley , because it has steep sides and a nearly flat floor. (The other side of the valley is missing in this cut-away diagram. </li></ul>