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Earth Science - Glaciers & Ice Ages

Earth Science - Glaciers & Ice Ages. Davidson Glacier near Haines, Alaska. Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight Glaciers form by accumulation and compaction of snow Packed snow becomes firn

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Earth Science - Glaciers & Ice Ages

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  1. Earth Science - Glaciers & Ice Ages

  2. Davidson Glacier near Haines, Alaska

  3. Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight Glaciers form by accumulation and compaction of snow Packed snow becomes firn Then refreezes to ice Glaciers

  4. Formation of Glacial Ice from Snow

  5. Glaciation Types • Alpine Glaciation: found in mountainous regions • Continental Glaciation: exists where a large part of a continent is covered by glacial ice - cover vast areas

  6. Types of Glaciers

  7. Alpine Glaciers • Are confined by surrounding mountains Types: • Cirque Glaciers – erode basins in mountainsides • Valley Glaciers – flow into preexisting stream valleys • Icecaps – form on mountaintops

  8. Types of Glaciers– Cirque Glacier Mount Edith Cavell, Jasper National Park, Canada

  9. Types of Glaciers – Valley Glacier Tongas National Forest, Alaska

  10. Types of Glaciers – Icecap and Continental Sentinal Range, Antarctica

  11. A Glacier’s Budget • A story of gains and losses • Gain snow in zone of accumulation • Lose ice in zone of ablation • Budget can be: • Positive (growth) • Static (unchanging) • Negative (net melting)

  12. A Glacier’s Budget Year round Snow Summer Rain Note that a glacier is a river. Even if the terminus doesn’t advance, still flows

  13. Iceberg Calving – Hubbard Glacier, Wrangell-St. Elias National Park, Alaska

  14. Erosion by Glaciers • Abrasion • Rocks embedded in glacier’s base make linear scratches and grooves in bedrock • Quarrying • Glacier breaks off and removes large blocks of rock

  15. Glacial Abrasion in Bedrock Source:Tom Bean

  16. Glacial Erosion – Roche Moutonee Yosemite NP, California

  17. Erosion by Glaciers (cont) • Alpine glaciers erode mountain slopes into horseshoe shaped basins called cirques • Erosion of multiple cirques erodes intervening rock, causing: • Horns: pointy peaks • Aretes: long serrated ridges • Cols: passes through the ridges.

  18. Alpine Glacial Erosion

  19. Alpine Glacial Erosion Origin of Hanging Valley

  20. Yosemite Falls

  21. Valley Glaciers • Erode a large quantity of bedrock and sediment • Convert V-shaped stream valleys into U-shaped glacial valleys.

  22. U-ShapedValley in Tracy Wilderness, Southeastern Alaska

  23. Seawater Flooded U-ShapedValleys: Fjords Bela Bela Fjord, BC

  24. Erosion by Continental Glaciation • Erosional Landforms much larger in scale than alpine glaciers • Huge U-shaped troughs, including: Finger Lakes, Great Lakes, Puget Sound, and Loch Ness were all once valleys excavated by glaciers

  25. Erosion of Preglacial Lowlands (Finger Lakes)

  26. Erosion of Preglacial Lowlands (Great Lakes of North America) Source:U.S. Dept. of Interior, USGS Eros Date Center

  27. Glacial Deposits or Drift • Glacial Till: unsorted, unstratified sediments deposited by melting ice. • May contain glacial erratics • Often accumulate at glacier’s terminus as a Moraine: hills of sediment left by a glacier’s retreat.

  28. Advance & Retreat: Moraines

  29. Large Granite Erratics

  30. Medial Moraines – Kennicott Glacier

  31. Effects of Glaciation • Change Climate –increased precipitation • Drop in sea-level:alter coastlines • Form continent-wide Dams • Divert streams – Ohio and Missouri rivers

  32. Lowered Sea-level - Landbridge

  33. Lowered Sea-level exposed continental shelf

  34. Giant Ripples of the Missoula Flooding

  35. Causes of Ice Ages • Plate Tectonics Moves Continents to Poles Raises mountains above snowline • Orbit Distances, Axis Tilt and Wobble • Moderates solar radiation past 65° N • Croll-Milankovitch Cycles ~ 100,000 years • Low summertime radiation causes glaciers to expand

  36. Glacier Distribution 20,000 ya Approximate Maximum

  37. Milankovitch Cycles 100,000 years

  38. 41,000 years

  39. Earth’s Past Ice Ages • PreCambrian Glaciation • 750 mya ice flowed from poles to tropics • Late Pennsylvanian & Permian Glaciation • covered South Africa, South America, India, Australia • Pleistocene Glaciation • most recent, ended about 10,000 years ago

  40. Pleistocene Glaciation • started 1.6 mya -30 advances and retreats • Latest retreat ended 10,000 years ago • “Little Ice Age” occurred 700 to 150 years ago, paralyzed Europe • Next glaciation period - ???

  41. Sustained warming since 1850 Athabaska Glacier, Columbia Icefield, W. Canada

  42. End of Glaciers

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