ch15

Report
Classroom presentations
to accompany
Understanding Earth, 3rd edition
prepared by
Peter Copeland and William Dupré
University of Houston
Chapter 15
Glaciers: The Work of Ice
Glaciers: the 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 motion
• Glaciers form where more snow
accumulates in winter than melts in
summer.
Polarized
Thin
Section
of Ice
Z. Xie/Lanzhou Institute of Glaciology, Academia Sinica, People’s Republic of China
Fig. 15.1
Types of Glaciers
alpine: restricted to mountainous
systems
continental: covers extremely large
areas
Antarctica: 12,500,000 km2 up to 3 km
thick, 80% of the ice on earth, 65% of
the fresh water
Greenland: 1,700,000 km2 3.2 km thick
Geophysical classification
Warm base - water at the bottom
Cold base - ice at the bottom
Activity classification
Live—moving
Dead—stagnant
Morphological classification
Valley glacier
Ice cap glacier
Ice shelf glacier
Sentinel Range, Antarctica
Betty Crowell
Fig. 15.2
Greenland
Ice Cap
Fig. 15.3
Fig. 15.4
Variations in the
Present Height of
the Snow Line
Fig. 15.5
Glacial growth: Accumulation
Transformation of snow into ice
Snow may be thought of as sediment,
Firn as sedimentary rock, and
Glacier ice as metamorphic rock.
Transformation
of Snow to
Glacial Ice
Fig. 15.6
Glacial shrinkage: Ablation
• Melting
• Iceberg calving
• Sublimination
• Wind erosion
Calving
Glacier,
Glacier
Bay,
Alaska
Tom Bean
Fig. 15.7
Glacial Budget
Fig. 15.8
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.
Stages of
Antarctic Ice Shelf
Retreat
Fig. 15.9
Fig. 15.10
Individual
Ice
Crystals
Z. Xie/Lanzhou Institute of Glaciology, Academia Sinica, People’s Republic of China
Fig. 15.1
Cold, Dry Glacier
Fig. 15.11
Wet Glacier
Fig. 15.12
Glacial Crevasses, New Zealand
John Turner/Tony Stone Images
Fig. 15.13
Ice Flow in
Typical
Temperate
Valley
Glacier
Fig. 15.14
Beardmore Glacier, Antarctica
Fast flow lines
Wolfgang Bayer/Bruce Coleman
Fig. 15.15
Ice Flow in a Continental Glacier
Fig. 15.16
Rates of motion
• Extremely variable from one glacier to
another
• Millimeters 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.
• Rates vary with position in the glacier.
Glacial erosion
Abrasion
ice is soft, tools do the job
striations, polish, friction cracks
Quarrying (plucking)
V-shaped valley vs. U-shaped
hanging valleys
Glacial Polish,
Striations,
and Grooves,
Glacier Bay
National Park,
Alaska
Carr Clifton
Fig. 15.17
Roche Moutonée
Fig. 15.18
Glacial Cirque, Alaska
Carlyn Iverson/Photo Researchers
Fig. 15.19
U-shaped
Glacial Valley,
Glacier
National Park,
Montana
Steve Kaufman/DRK
Fig. 15.20
Creation of
Hanging
Valleys and
Associated
Waterfalls,
Before and
After
Glaciation
Fig. 15.21
Glacial deposits
1. Erratics
2. Glacial drift
Unsorted
till
kame
Sorted
outwash
eskers
3. Morrain: ridges of till
End
Lateral
Medial
McCarthy Fjord, Kenai Fjords
National Park, Alaska
Peter Kresan
Fig. 15.22
Glacial Till
on the
Eastern Side
of the Sierra
Nevada
Martin Miller
Fig. 15.23
Glacial Deposits
Fig. 15.24
Drumlins in Wisconsin
Tom Bean/DRK
Fig. 15.25
Esker in Canada
Tim Hauf Photography/Visuals Unlimited
Fig. 15.26
Kames and Kettles in New Zealand
Kame
Kettle
E.R. Degginger
Fig. 15.26
Varves Formed in Glacial Lake
John S. Shelton
Fig. 15.27
Lateral
Moraines
Medial
Moraines
Stephen J. Krasemann/DRK Photo
Evolution
of an
Outwash
Kettle
Fig. 15.28
Typical “Hummocky” Terrain of
Glacial Till
John S. Shelton
Fig. 15.30
Pleistocene continental glaciation
Great ice sheets extended into
temperate
regions 4 times in the past:
Wisconsin
0.20 – 0.018 Ma
0.20 m.y.
Illinoian
0.55 – 0.40 Ma
0.40 m.y.
Kansan
1.40 – 0.95 Ma
0.25 m.y.
Nebraskan
2.00 – 1.75 Ma
Advances and retreats
of continental glaciers
Worldwide and essentially
instantaneous
Sea level changes
lots of water in glaciers: during last ice
age sea level lowered by ~130 m
shoreline 100 km from NYC - Bering
Strait, English Channel, Indonesia
If all ice in glaciers today would melt,
sea level would rise 65m: Florida,
Egypt, Hong Kong, London, Houston
Glaciation in the geologic record
Ancient glacial deposits (till,
dropstones) indicate other
periods of significant
glaciation.
Late PC, Ordovician, Permian
Distribution of
Permafrost in
the Northern
Hemisphere
Fig. 15.29
Glaciation in
North
America
Fig. 15.31
What causes ice ages?
• Variations in Earth's orbit
• Changes in the atmosphere
• Changing position of the continents
• Changes in circulation of sea water
• Sliding of Antarctic ice sheet
No single one of these explains all ice
ages – must be some combination.
Changes in Oxygen Isotope Ratios
in Marine Fossils
Fig. 15.32
August, 18,000 B.P.
Fig. 15.33
Flooding
Along the
Bay of
Bengal,
Bangladesh
James P. Blair/National Geographic
Components
of the EarthSun Orbital
Variation
Fig. 15.34
Thermohaline Oceanic Circulation
Copyright N.W. Driscoll, Woods Hole Oceanographic Institute
Fig. 15.35
Ice cores from
the Vostok
Station,
Antarctica
After J.W.C. White (1993)
R.J. Delmas, Laboratorie de glaciologie et geophysique de l’environnement, Centre National de la Recherche Scientifique

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