Glaciers: the Work of Ice Stephen J. Krasemann/DRK Photo.
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Transcript of Glaciers: the Work of Ice Stephen J. Krasemann/DRK Photo.
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Glaciers: Glaciers: thethe Work of Ice Work of Ice
Stephen J. Krasemann/DRK Photo
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Glacier
• Body of ice, snow, firn, and meltwater lying wholly or mostly on land showing evidence of present or former movement
• Glaciers form where more snow accumulates in winter than melts in summer - above snowline
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Variations in the Variations in the Present Height of Present Height of
the Snow Linethe Snow Line
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Types of Glaciers
alpinealpine: restricted to mountainous systems
continentalcontinental: covers extremely large areas - ice caps, ice sheets
AntarcticaAntarctica: 12,500,000 km2 up to 3 km thick, 80% of the ice on earth, 65% of the fresh water
Greenland:Greenland: 1,700,000 km2 3.2 km thick
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Common types of alpine
glaciers
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Valley Glaciers, Denali National Park
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Greenland Greenland Ice CapIce Cap
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Betty Crowell
Sentinel Range, Antarctica
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Glacial growth: Accumulation
Transformation of snow into iceTransformation of snow into ice
SnowSnow may be thought of as sediment,
FirnFirn as sedimentary rock, and
Glacier iceGlacier ice as metamorphic rock.
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Transformation Transformation of Snow to of Snow to Glacial IceGlacial Ice
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Z. Xie/Lanzhou Institute of Glaciology, Academia Sinica, People’s Republic of China
Polarized
Thin Section of Ice
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Glacial BudgetGlacial Budget
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Glacial shrinkage: Ablation
• Melting
• Iceberg calving
• Sublimination
• Wind erosion
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Tom Bean
Calving Glacier,Glacier
Bay,Alaska
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Iceberg near AntarcticaIceberg near Antarctica
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Mechanisms of motion in glaciers
• Type of motion depends on depth.
• Upper 50–100 m: brittle
• > 100 m: plastic (layers of ice slide past
each other)
• Individual slips extremely small
• Motion at base can be by slip or lubricated by water.
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Cold, Dry GlacierCold, Dry Glacier
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Wet GlacierWet Glacier
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Rates of motion
• Extremely variable from one glacier to another
• Millimeters to meters per dayMillimeters to meters per day
• Some glaciers move in surges: periods of rapid movement following periods of quiescence.
• During surge, rates may be 50 m/day.During surge, rates may be 50 m/day.
• Rates vary with position in the glacier & season of the year.
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Glacial Glacial flow and flow and
basal basal slidingsliding
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Ice Flow in Ice Flow in Typical Typical
Temperate Temperate Valley Valley GlacierGlacier
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John Turner/Tony Stone Images
Glacial Crevasses, New Zealand
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Ice Flow in a Continental GlacierIce Flow in a Continental Glacier
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Wolfgang Bayer/Bruce Coleman
Beardmore Glacier, AntarcticaBeardmore Glacier, Antarctica
Fast flow lines
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Stages of Stages of Antarctic Ice Shelf Antarctic Ice Shelf
RetreatRetreat
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Glacial erosion
AbrasionAbrasion - ice is soft, tools do the job - striations, polish, friction cracks
Quarrying (plucking)Quarrying (plucking)
U-shaped valleys & hanging valleys
cirques, horns, artet, rock flour
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Glacial Polish, Striations,
and Grooves, Glacier Bay
National Park,Alaska
Carr Clifton
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Glacial Glacial grooves and grooves and
striations striations at the base of at the base of
the Matterhornthe Matterhorn
S. C. Porter
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Roche Moutonée
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Asymmetrical glacial sculpturingAsymmetrical glacial sculpturing
S. C. Porter
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Direction of ice flowDirection of ice flow
S. C. Porter
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Carlyn Iverson/Photo Researchers
Glacial Cirque, AlaskaGlacial Cirque, Alaska
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U-shaped Glacial Valley,
Glacier National Park,
Montana
Steve Kaufman/DRK
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U-shaped U-shaped valleys and valleys and
fjords in fjords in northeasternortheastern Canadan Canada
S. C. Porter
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Peter Kresan
McCarthy Fjord, Kenai Fjords National Park, Alaska
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Creation of Creation of Hanging Hanging
Valleys and Valleys and Associated Associated Waterfalls, Waterfalls, Before and Before and
After After GlaciationGlaciation
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Glacial deposits
1. ErraticsErratics2. Glacial driftGlacial drift
Unsorted SortedTILL
outwashkame eskers
loess/varves3. MorainsMorains: ridges of tillEnd, Lateral & Medial
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S. C. Porter
Glacial erratic
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Glacial Till on the
Eastern Side of the Sierra
Nevada
Martin Miller
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S. C. Porter
Glacial tillGlacial till
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Varves Formed in Glacial Lake
John S. Shelton
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Glacial DepositsGlacial Deposits
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Stephen J. Krasemann/DRK Photo
LateralMoraines
MedialMoraines
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Courtesy USGS
Surging tributary glacierSurging tributary glacier
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Terminal moraineTerminal moraine
Courtesy Gerald Osborn
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Melting Ice
ResultingFeatures
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Tom Bean/DRK
Drumlins in Wisconsin
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Tim Hauf Photography/Visuals Unlimited
Esker in CanadaEsker in Canada
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E.R. Degginger
Kames and Kettles in New Zealand
Kettle
Kame
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John S. Shelton
Typical “Hummocky” Terrain Typical “Hummocky” Terrain of Glacial Tillof Glacial Till
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Distribution of Distribution of Permafrost in Permafrost in the Northern the Northern HemisphereHemisphere
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Lateral variations in permafrost in Siberia
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GLACIATIONSGLACIATIONS
• Several periods in past• Worldwide & essentially
instantaneous (10 years)• Continental glaciers advance
and retreat several times•
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Pleistocene continental glaciation
Great ice sheets extended into temperate regions 4 times in the past 2 million years:
Wisconsin 0.20 – 0.018 Ma
Illinoian 0.55 – 0.40 Ma
Kansan 1.40 – 0.95 Ma
Nebraskan 2.00 – 1.75 Ma
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Isotopic record Isotopic record of changing of changing ice volume ice volume
over the past over the past 2 million years 2 million years
based onbased on deep-sea cores deep-sea cores
Fig. 12.32
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Changes in Oxygen Isotope Ratios in Changes in Oxygen Isotope Ratios in Marine FossilsMarine Fossils
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Sea level changes
Lots of water in glaciers - during last ice age sea level lowered by ~130 m130 m
* shoreline 100 km from NYC - Bering Strait, English Channel, Indonesia
(If all ice in glaciers today melted, sea level would rise 65m65m - Florida, Egypt, Hong Kong, London, Houston would be gone)
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Glaciation in the geologic record
1. Ancient glacial deposits (till, dropstones, striations) indicate other periods of significant glaciation.
2. Late PC (Snowball Earth), Ordovician, Permian
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Glaciation in Glaciation in North North
AmericaAmerica
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What causes ice ages?
• Variations in Earth's orbitVariations in Earth's orbit
• Changes in the atmosphereChanges in the atmosphere
• Changing position of the continentsChanging position of the continents
• Changes in circulation of sea waterChanges in circulation of sea water
• Sliding of Antarctic ice sheetSliding of Antarctic ice sheet
No single one of these explains all ice
ages – must be some combination.
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Ice cores from the Vostok
Station, Antarctica
R.J. Delmas, Laboratorie de glaciologie et geophysique de l’environnement, Centre National de la Recherche Scientifique
After J.W.C. White (1993)
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Copyright N.W. Driscoll, Woods Hole Oceanographic Institute
Thermohaline Oceanic Circulation
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Retreating Rhone GlacierRetreating Rhone Glacier
S. C. Porter
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