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Glaciers and Glaciation

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Glaciers and Glaciation

  1. 1. GLACIERS AND SEA ICE
  2. 2. Glaciers <ul><li>A large, slow-moving mass of ice </li></ul><ul><li>Formed from compacted layers of snow </li></ul><ul><li>Glaciers slowly deform and flow in response to gravity and high pressure. </li></ul><ul><li>Cover about 10% of Earth’s landmass. </li></ul>
  3. 3. Extent of Glaciers <ul><li>Glaciers cover vast areas of polar regions, are found in mountain ranges of every continent, and are restricted to the highest mountains in the tropics. The </li></ul>The Baltoro Glacier in the Karakora Mountains, Pakistan. At 62 kilometres (39 mi) in length, it is one of the longest alpine glaciers on earth.
  4. 4. Glaciation <ul><li>The process of glacier growth and establishment is called glaciation . </li></ul><ul><li>Glaciers are sensitive monitors of climate conditions and are crucial to both world water resources and sea level variation. </li></ul>Folgefonni Glacier in Sorfjorden, Norway. Picture taken by Yann Arthus-Betrand.
  5. 5. Types of Glaciers <ul><li>Alpine glaciers , which are found in mountain terrains </li></ul><ul><li>Continental glaciers-ice sheets , which can cover larger areas </li></ul><ul><li>Glaciers are also categorized by thermal characteristics, climate setting, and behavior. </li></ul>Aletsch Glacier, Switzerland, the largest glacier in the European Alps
  6. 6. Alpine Glaciers <ul><li>Confined to mountain valleys </li></ul><ul><li>Flow from higher to lower elevations </li></ul><ul><li>Shape of alpine glacier is controlled by the shape of the valley </li></ul>A valley (or alpine) glacier in Alaska
  7. 7. Tidewater Glaciers <ul><li>Glaciers that flow into the sea. </li></ul><ul><li>Involved in the formation of ice bergs. </li></ul><ul><li>Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water. </li></ul>Hubbard Glacier is the largest tidewater glacier in Alaska
  8. 8. Calving Glaciers http://www.youtube.com/watch?v=bYH2Df-evNs
  9. 9. Floating Sea Ice
  10. 10. Ice Cap <ul><li>An ice mass that covers less than 50 000 km² of land area </li></ul><ul><li>Ice caps are not constrained by topographical features </li></ul><ul><li>their dome is usually centered on the highest point of a massif . </li></ul><ul><li>Ice flows away from this high point (the ice divide ) towards the ice cap's periphery. </li></ul>Vatnajökull, Iceland
  11. 11. Ross Ice Shelf (Sheet) <ul><li>Masses of ice covering more than 50 000 km² are termed an ice sheet. </li></ul><ul><li>Thick plates of ice, fed by glaciers, that float atop an ocean. </li></ul><ul><li>The presence of the shelves acts as &quot;brakes&quot; for the glaciers. </li></ul><ul><li>They also moderate the amount of melting that occurs on the glaciers' surfaces and act as a breaking force for glaciers. </li></ul><ul><li>It’s about the size of France (area of roughly 487 000 km², and about 800 km across) </li></ul>
  12. 12. Continental Glaciers <ul><li>Not confined by topography </li></ul><ul><li>Cover the entire surface beneath them. </li></ul><ul><li>Flow outward in all directions. </li></ul><ul><li>Not visibly affected by the landscape underneath. </li></ul><ul><li>Antarctica and Greenland are the only places where continental ice sheets currently exist. </li></ul><ul><li>Contain vast quantities of fresh water. </li></ul>Part of the Greenland Ice Sheet; Covers about 1.8 million Km2
  13. 13. Glacier Formation <ul><li>Form where snow and ice accumulation exceed snow and ice melt </li></ul><ul><li>Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser and denser firn </li></ul><ul><li>Firn is partially-compacted neve. </li></ul><ul><li>Neve is a young, granular type of snow which has been partially melted, refrozen and compacted. </li></ul>Firn from South Cascade Glacier, 80x magnified.
  14. 14. Growth of Glaciers <ul><li>Glaciers grow or recede as a function of the balance between accumulation and ablation of snow and ice. </li></ul><ul><li>The accumulation zone is a region where snowpack or superimposed ice accumulation persists. </li></ul><ul><li>The ablation zone is the region where all of the snow has melted away and bare glacier ice is exposed. </li></ul>
  15. 15. Crevasses in Glaciers <ul><li>Crevasses are common in the upper parts of glaciers when the ice is subjected to tension. </li></ul>Crevasses in a continental glacier near the Ross Sea .
  16. 16. Radioglaciology <ul><li>Study of glaciers and ice sheets using radar. </li></ul><ul><li>It employs a geophysical method similar to ground-penetrating radar. </li></ul><ul><li>Uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum. </li></ul><ul><li>Detects the reflected signals from subsurface structures. </li></ul><ul><li>GPR can be used in a variety of media, including rock, soil, ice, fresh water, pavements and structures. </li></ul><ul><li>It can detect objects, changes in material, and voids and cracks. </li></ul>
  17. 17. National Snow and Ice Data Center http://www.nsidc.org/ <ul><li>center in support of polar and cryospheric research </li></ul><ul><li>maintains information about snow cover, avalanches, glaciers, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice, paleoglaciology , and ice cores </li></ul>
  18. 18. Anatomy of a Glacier <ul><li>A cirque is an amphitheatre-like valley, or valley head, formed at the head of a glacier by erosion. </li></ul><ul><li>A medial moraine is a ridge of moraine that runs down the centre of a valley floor. It is formed when two glaciers meet and the debris on the edges of the adjacent valley sides join and is carried on top of the enlarged glacier. </li></ul>
  19. 19. The Glacial Budget <ul><li>The glacial budget is the total of accumulation and ablation for a glacier. </li></ul><ul><li>In winter the budget is equal or can exceed melt causing the glacier to grow, but in summer snow and ice melt exceed deposition. </li></ul>
  20. 20. Glacial Surges <ul><li>A glacial surge is a short-lived episode of accelerated flow in which the surfaces breaks into a maze of crevasses and its terminus advance noticeably. </li></ul><ul><li>The fastest glacial surge ever recorded was in 1953 in the Kutiah Glacier in Pakistan, the glacier advanced 12 km in 3 months. </li></ul>
  21. 21. Glacial Movement Variables <ul><li>Temperature of the area </li></ul><ul><li>The slope of the glacier </li></ul><ul><li>The bed's sediment size </li></ul><ul><li>The amount of meltwater from the glacier </li></ul><ul><li>The glacier's size </li></ul>
  22. 22. Basal Sliding <ul><li>Basal Sliding is the act of a glacier sliding over the bed before it due to meltwater under the ice acting as a lubricant. </li></ul>
  23. 23. Anatomy of a Receding Glacier I <ul><li>Lateral moraines are parallel ridges of debris deposited along the sides of a glacier. </li></ul><ul><li>A terminal moraine forms at the end of the glacier called the snout and marks the maximum advance of the glacier. </li></ul><ul><li>Ground moraines are till covered areas with irregular topography and no ridges often forming gently rolling hills or plains. </li></ul>
  24. 24. Sediment Transport by Valley Glaciers The dark material on the glacier is sediment.
  25. 25. Glacial Outwash <ul><li>A sandur is a glacial outwash plain formed of sediments deposited by meltwater at the terminus of a glacier. </li></ul><ul><li>An outwash plain might contain surface meandering streams that rework the original deposits. </li></ul><ul><li>The flow pattern of glacial rivers across sandar is typically diffuse and unchannelized. </li></ul>The western edge of Skeiðarársandur in Iceland shows the diffuse drainage channels typical of sandur.
  26. 26. Varve <ul><li>A varve is an annual layer of sediment or sedimentary rock. </li></ul><ul><li>The light layer usually comprises a coarser laminaset of silt and fine sand deposited under higher energy conditions when meltwater introduces sediment load into the lake water. </li></ul>Varve deposits from a glacial lake.
  27. 27. Anatomy of a Receding Glacier II <ul><li>A kettles are fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming buried partially to wholly by glacial outwash. </li></ul><ul><li>A kame is a geological feature, an irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier. </li></ul><ul><li>An esker is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions. </li></ul>
  28. 28. Glacial Polishing
  29. 29. Glacial Erratics <ul><li>A glacial erratic is a piece of rock that deviates from the size and type of rock native to the area in which it rests. </li></ul><ul><li>These rocks were carried to their current locations by glacial ice, often over hundreds of kilometres. </li></ul><ul><li>Erratics can range in size from pebbles to large boulders. </li></ul>
  30. 30. Glacial Maximums <ul><li>The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles. </li></ul><ul><li>Existed during the Pleistocene between c. 95,000 and c. 20,000 years before the present day. </li></ul><ul><li>Some parts were up to 2 miles think, depressing the crust up to 300 meters. </li></ul>
  31. 31. Climate Change <ul><li>Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate. </li></ul><ul><li>The Earth's axis completes one full cycle of precession approximately every 26,000 years. </li></ul><ul><li>The elliptical orbit rotates leads to a 21,000-year cycle between the seasons. </li></ul><ul><li>Earth's rotational axis moves between 22.1 degrees to 24.5 degrees creating a 41,000-year cycle. </li></ul>
  32. 32. Glacial Isotasy <ul><li>Formed during the recession of the Pleistocene ice shelf. </li></ul><ul><li>Rebound began in the southern region and proceeded north. </li></ul><ul><li>Lakes were formed because of crustal depression and melting of receding ice sheet. </li></ul>A satellite image of the Great Lakes.
  33. 33. State of Glaciers Today <ul><li>Most are melting because of climate change. </li></ul><ul><li>Many scientist believe that humans have greatly contributed to a natural melting cycle by adding carbon dioxide to the atmosphere causing global warming . </li></ul>

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