EART 3 Geology of National Parks 22704

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EART 3- Geology of National Parks 2/27/04

• OUTLINE
• What is a Glacier and how does it move
• Glacial Landscapes
• Ice Ages
• CONCEPTS
• Ice as metamorphic rock
• Brittle vs. ductile deformation
• Climate controls

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Glacier- permanent body of ice that moves
downslope
Cirque glacier-occupies a bowl shaped depression
on a mountain Valley glacier-flows from a cirque
along a valley floor Piedmont- broad lobe of ice
that terminates on open slopes Ice sheet-
continent size ice mass
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Grinnell Glacier, Glacier NP
Valley Glacier
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How do glaciers move?

• 1. Internal Flow- flow by ice crystals shearing
  past each other (Ductile deformation)
• 2. Basal sliding- sliding at the base of the
  glacier aided by a thin layer of water

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Challenger Glacier, North Cascades NP
Crevasses brittle deformation Internal flow
below- ductile deformation
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Erosional Glacial Landforms
U shaped valley- V shaped river valley widened by
glacier Hanging valley- U shaped valley carved by
smaller tributary glacier not as deep as main
glacial valley Cirque- bowl shaped depression
where alpine glaciers originate Arete- sharp
peaked ridge surrounded by cirques Horn- pointed
peak where aretes meet
Glacial polish-smoothed rock surface due to ice
movement Roches mountonees- small ridge with a
smooth gradual side and a steep drop Tarn- small
lake at the base of a cirque
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U Shaped Valley Yosemite NP
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Hanging Valley Bridal Veil Falls, Yosemite NP
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Chasm Lake, Rocky Mtn. NP
Cirque
Tarn
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Arete
North Cascades NP
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Pilot Peak, outside Yellowstone NP
Horn
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Yosemite NP
Glacial polish
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Acadia NP
Roche Mountonees
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Depositional Glacial Landforms
Glacial till-sediment deposited by ice and
unsorted Outwash- till that has been carried and
sorted by meltwater Moraine- glacial till
accumulated at the edge (lateral), the end
(terminal), or between (medial) glaciers Glacial
erratic- large boulder carried by a glacier and
deposited
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Glacial erratic
Yosemite NP
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Yosemite NP
Glacial till
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Mills Moraine Rocky Mountain NP
Lateral Moraine
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Grand Teton NP
Terminal Moraine
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Ice Ages
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Oxygen Isotopes
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What Causes Ice Ages?

• Changes in the orbital parameters of the Earth
  that place it farther from the sun
• Reduction in the concentration of certain gases
  in the atmosphere (greenhouse gases)

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Orbital Parameters
Precession of the equinoxes Obliquity
Eccentricity
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Greenhouse Gases