Glaciers and the Great Ice Ages

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Glaciers and the Great Ice Ages
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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)

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Why did the climate change so drastically and
repeatedly?

• Climate change and variations in Earths orbit
• Eccentricity elliptical to nearly circular
  cycles
• Obliquity cyclic changes in tilt of axis
• Precession cyclic change inwobble of the axis
• Variations affect amount and distribution of
  solar energy received by Earth

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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

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Glacial Flow

• Ice begins to flow (plastic deformation) under
  the influence of gravity
• Glacier mass of flowing ice

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Glacial Flow

• Glacial 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)

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Glaciers and Landscapes

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

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Erosion by Glaciers

• Striations scratchmarks made as ice drags
  rocks across bedrock

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Erosion by Glaciers

• Modifies V shaped river valleys to a U shape

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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

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Deposition by glaciers

• Lacustrine sediments
• Lakes form between melting edge of ice and
  obstructions (often deposits of till)
• Fine silt and clay settle 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

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Glaciers and Landforms

• Characteristic landforms

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New Yorks Glacial Landscape

• Shaped by Erosion
• and Deposition

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Glaciers and New Yorks Landscape

• Great Lakes Erie and Ontario
• Glacially widened and deepened E-W stream valleys
  
• Finger Lakes
• Glacially deepened N-S stream valleys
• Mohawk Valley misfit stream
• Glacially widened and deepened E-W stream valley
• Glacial Lake Albany drained when ice left
  Hudson Valley

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Glaciers and New Yorks Landscape

• Susquehanna Valley modified to U shape
• Dammed by till at Wells Bridge (near Otego)
• Dam broke and lake drained

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Glaciers and New Yorks Landscape

• Hudson Valley a fjord
• Glacially deepened N-S stream valley
• Flooded when sea level rose
• Salt water as far north as Poughkeepsie
• Tides affect river level as far north as Troy
• Ocean freighters can sail up to Albany an
  inland seaport

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Kensetts Hudson - Fjord
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Palisades (igneous rock) along the Hudson Fjord
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Hudson Fjord, Long Island Sound,Moraines and
Outwash of Long Island
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Glaciers and New Yorks Landscape

• Long Island
• Two terminal moraines
• Outwash plain
• Long Island Sound - Glacially widened stream
  valley flooded by rising sea level

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Other Glacial Features

• Outwash channels Niagara River
• Hanging valleys and waterfalls very prominent
  in the Finger Lakes
• Kettle lakes
• Drumlins

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Churchs Niagara Falls Outwash Channel
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Glaciers and New Yorks Economy

• Thick, fertile soils developed on till and
  outwash foundation of agriculture in state
• Microclimate associated with Lakes
• Water moderates climate
• Warmer in winter, cooler in summer
• Ideal for growing grapes/producing wine
• Aquifers especially in outwash
• Sand and gravel for construction