Glaciers: the Work of Ice Stephen J. Krasemann/DRK Photo.
-
Upload
nathan-marshall-cox -
Category
Documents
-
view
225 -
download
0
Transcript of Glaciers: the Work of Ice Stephen J. Krasemann/DRK Photo.
Glaciers: Glaciers: thethe Work of Ice Work of Ice
Stephen J. Krasemann/DRK Photo
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
Variations in the Variations in the Present Height of Present Height of
the Snow Linethe Snow Line
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
Common types of alpine
glaciers
Valley Glaciers, Denali National Park
Greenland Greenland Ice CapIce Cap
Betty Crowell
Sentinel Range, Antarctica
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.
Transformation Transformation of Snow to of Snow to Glacial IceGlacial Ice
Z. Xie/Lanzhou Institute of Glaciology, Academia Sinica, People’s Republic of China
Polarized
Thin Section of Ice
Glacial BudgetGlacial Budget
Glacial shrinkage: Ablation
• Melting
• Iceberg calving
• Sublimination
• Wind erosion
Tom Bean
Calving Glacier,Glacier
Bay,Alaska
Iceberg near AntarcticaIceberg near Antarctica
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.
Cold, Dry GlacierCold, Dry Glacier
Wet GlacierWet Glacier
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.
Glacial Glacial flow and flow and
basal basal slidingsliding
Ice Flow in Ice Flow in Typical Typical
Temperate Temperate Valley Valley GlacierGlacier
John Turner/Tony Stone Images
Glacial Crevasses, New Zealand
Ice Flow in a Continental GlacierIce Flow in a Continental Glacier
Wolfgang Bayer/Bruce Coleman
Beardmore Glacier, AntarcticaBeardmore Glacier, Antarctica
Fast flow lines
Stages of Stages of Antarctic Ice Shelf Antarctic Ice Shelf
RetreatRetreat
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
Glacial Polish, Striations,
and Grooves, Glacier Bay
National Park,Alaska
Carr Clifton
Glacial Glacial grooves and grooves and
striations striations at the base of at the base of
the Matterhornthe Matterhorn
S. C. Porter
Roche Moutonée
Asymmetrical glacial sculpturingAsymmetrical glacial sculpturing
S. C. Porter
Direction of ice flowDirection of ice flow
S. C. Porter
Carlyn Iverson/Photo Researchers
Glacial Cirque, AlaskaGlacial Cirque, Alaska
U-shaped Glacial Valley,
Glacier National Park,
Montana
Steve Kaufman/DRK
U-shaped U-shaped valleys and valleys and
fjords in fjords in northeasternortheastern Canadan Canada
S. C. Porter
Peter Kresan
McCarthy Fjord, Kenai Fjords National Park, Alaska
Creation of Creation of Hanging Hanging
Valleys and Valleys and Associated Associated Waterfalls, Waterfalls, Before and Before and
After After GlaciationGlaciation
Glacial deposits
1. ErraticsErratics2. Glacial driftGlacial drift
Unsorted SortedTILL
outwashkame eskers
loess/varves3. MorainsMorains: ridges of tillEnd, Lateral & Medial
S. C. Porter
Glacial erratic
Glacial Till on the
Eastern Side of the Sierra
Nevada
Martin Miller
S. C. Porter
Glacial tillGlacial till
Varves Formed in Glacial Lake
John S. Shelton
Glacial DepositsGlacial Deposits
Stephen J. Krasemann/DRK Photo
LateralMoraines
MedialMoraines
Courtesy USGS
Surging tributary glacierSurging tributary glacier
Terminal moraineTerminal moraine
Courtesy Gerald Osborn
Melting Ice
ResultingFeatures
Tom Bean/DRK
Drumlins in Wisconsin
Tim Hauf Photography/Visuals Unlimited
Esker in CanadaEsker in Canada
E.R. Degginger
Kames and Kettles in New Zealand
Kettle
Kame
John S. Shelton
Typical “Hummocky” Terrain Typical “Hummocky” Terrain of Glacial Tillof Glacial Till
Distribution of Distribution of Permafrost in Permafrost in the Northern the Northern HemisphereHemisphere
Lateral variations in permafrost in Siberia
GLACIATIONSGLACIATIONS
• Several periods in past• Worldwide & essentially
instantaneous (10 years)• Continental glaciers advance
and retreat several times•
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
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
Changes in Oxygen Isotope Ratios in Changes in Oxygen Isotope Ratios in Marine FossilsMarine Fossils
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)
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
Glaciation in Glaciation in North North
AmericaAmerica
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.
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)
Copyright N.W. Driscoll, Woods Hole Oceanographic Institute
Thermohaline Oceanic Circulation
Retreating Rhone GlacierRetreating Rhone Glacier
S. C. Porter