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Glaciers and the Great Ice Ages

Glaciers and the Great Ice Ages

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Glaciers and the Great Ice Ages

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  1. Glaciers and the Great Ice Ages

  2. Pleistocene Epoch:the Great Ice Ages • 2.0 Ma to 10,000 years ago • Four (or more) distinct episodes expansion and melting of ice sheets (continental glaciers)

  3. Why did the climate change so drastically and repeadedly? • Climate change and variations in Earth’s orbit • Eccentricity: elliptical to nearly circular cycles • Obliquity: cyclic changes in tilt of axis • Precession: cyclic change in”wobble” of the axis • Variations affect amount and distribution of solar energy received by Earth

  4. How does a glacier form? • Cold climate is necessary • Annual snow accumulation is greater than annual rate of melting • Snow builds up over time • Snow recrystallizes to ice

  5. Glacial Flow • Ice begins to flow (plastic deformation) under the influence of gravity • Glacier = mass of flowing ice

  6. Glaciers are dynamic • Flow is constant • Some parts of glacier are melting • Rate of accumulation vs. rate of melting determines if glacier will advance or if end of glacier will melt back (glaciers never flow backwards)

  7. Glaciers and Landscapes • Flowing ice picks up sediment, soil, etc. • Breaks loose pieces of bedrock • Modifies landscape by erosion and deposition

  8. Erosion by Glaciers • Striations: “scratch”marks made as ice drags rocks across bedrock

  9. Erosion by Glaciers • Modifies “V” shaped river valleys to a “U” shape

  10. Deposition by Glaciers • Erratics – pieces of “exotic” rock left by glacier • Till – unsorted, unstratified sediments dumped by ice • Outwash – sorted and stratified sand and gravel deposited by meltwater

  11. Deposition by glaciers • Lacustrine sediments • Lakes form between melting edge of ice and obstructions (often deposits of till) • Fine silt and clay settle to the bottom in calm water • Clay may be used in pottery and brick making • If lakes drain or fill with sediment: • bogs and swamps – ecologically important wetlands • Water-logged lacustrine sediments may cause tilting and sinking of buildings constructed on them

  12. Glaciers and Landforms • Characteristic landforms