glaciers and ice sheetshomepages.wmich.edu/~kehew/geos1000/ch13_glaciers.pdfglaciers and ice sheets...
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Glaciers and Ice Sheets• Cryosphere
– The perennially frozen part of the
hydrosphere
• Components of the cryosphere
– Glaciers
• A semi-permanent or perennially
frozen body of ice,
• Consists largely of re-crystallized
snow
• Moves under the pull of gravity
– Temperate glaciers
– Polar glacier
– Ice sheets
– Ice shelves, ice bergs
GLACIER TYPES AND
FEATURES
What are glaciers?
• Masses of ice that are thick enough to flow under their own weight.
Emerald Glacier
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Glaciers and Ice Sheets
• How glaciers form
– Snow that survives for more than a year gradually becomes
denser until it is no longer penetrable by air and becomes
glacier ice.
– Further changes happen as the glacial ice is buried deeper
(increasing pressure)
Glacial Ice
• Glacial Ice is snow that has been recrystallized and densified (spec. gravity = 0.9) It is commonly banded because of formation of layers at different times. It is blue in color because it reflects blue wavelengths and absorbs others.
Snow = 0.1
Firn = 0.5-0.8
Glacier ice = 0.9
What kinds of glaciers are
there?• Ice Sheets-dome shape, >50,000 km2
• Ice Caps-dome shape, <50,000 km2
• Ice Fields
• Valley Glaciers
• Cirque Glaciers
• Tidewater Glaciers and Ice Shelves
• Small Glaciers
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Ice Sheets- Dome shaped masses of ice
that are greater than 50,000 km2 in area.
The Laurentide Ice Sheet
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Ice Caps- Dome shaped masses of ice
less than 50,000 km2 in area
Eyjafjallajokull-Iceland
Outlet (valley) glacier from ice cap. Notice moraine, proglacial
lake, outwash plain.
Top of an ice dome from the air
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Piedmont lobe of an Icelandic ice cap
Ice Fields – Non dome-shaped masses of ice of
large areal extent in mountainous areas.
Mountain peaks project above them.
Wapta Ice Field
Climbers ascending to top of ice field
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Top of Wapta Ice Field
Valley Glaciers-Long narrow glaciers that flow
down hill in troughs cut into bedrock
Athabasca Glacier- Note moraines.
Ruth Glacier-Alaska
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Alaska
Chamonix
Terminus of Kahiltna Glacier, Alaska
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Icelandic glacier in previously formed glacial trough
Solheimajokull, Iceland, 1971
Solheimajokull Glacier, 1992
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Solheimajokull Glacier terminus, 1992
Cirque Glaciers
• Small
glacier that
forms in a
bowl-
shaped
depression
called a
cirque.
Cirque was formed by a glacier during the last ice age.
Grinnell Glacier-Glacier National Park
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Tidewater Glaciers and Ice
Shelves:Glaciers that terminate in water
Harvard and Yale Glaciers-Prince William Sound
Tidewater glaciers: grounded at the end of the
glacier; does not form an ice shelf
Yale Glacier-Prince William Sound
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Ice shelf, Antarctica
Edge of an ice shelf. The height of the edge is 30 m and the shelf
extends several hundred meters below sea level.
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Larsen Ice Shelf, 2002.
Shelf is undergoing
catastrophic collapse due
to global warming.
Tabular ice bergs
Breakup of ice shelf margin to form tabular ice bergs
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Emerald Glacier, 2002, Canadian Rockies
SMALL GLACIERS
Bow Lake
Glaciers and Ice Sheets
• How glaciers grow and shrink
– A glacier is measured using the amount of snow
(winter) and the amount of melting (summer).
– The difference between accumulation and ablation is a
measure of the glacier’s mass balance
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Glacier Mass Balance (budget)
• Accumulation area
• Ablation area
• Equilibrium line
Glaciers and Ice Sheets
Glaciers and Ice Sheets
• How glaciers move
– Glaciers move because
of the pull of gravity
– Ice in the central part of
the glacier moves faster
then the sides, and the
uppermost moves faster
than the lower layers
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Glaciers and Ice Sheets
2 types of movement
•Internal deformation (creep)
•Basal sliding
Glaciers and Ice Sheets
• Internal flow
– Ice moves in a glacier
through a combination
of ductile deformation
at depth and brittle
deformation at the
surface
– Crevasse
• A deep gaping fissure in
the upper surface of a
glacier
Glaciers and Ice Sheets
• Basal sliding
– Ice at the bottom of a
glacier slides across its
bed (the rock or sediment
which the glacier rests
on)
– The glacial landscape
• Glacier acts like a file,
sled, and plow
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• Glacial erosion
– Abrasion
• Glacial striations
– Plucking (quarrying); removal
of large blocks
– Large scale erosion
• Glacial troughs (deep valleys
with a U-shaped profile)
• Cirques
Arete: thin ridge between
2 cirques
Geiranger fjord, Norway
Troughs and fjords
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Glacial abrasion: striations
Striations, polish, Maine
Plucking
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Canadian Rockies
Plucking: large blocks removed as glacier moves over
Glaciers and Ice Sheets
• Glacial deposition
– Till
• A mixture of crushed rock,
clay, sand, pebbles, cobbles,
and boulders deposited by a
glacier
– Moraine
• A ridge or pile of debris that
has been, or is being,
transported by a glacier
• Generally formed in the
middle of the glacier
(medial); at the sides
(lateral); or at the end of the
glacier (terminal)
Michigan impacted by
three lobes of the LIS
Glacial deposits 3-180
meters thick
Overlie sedimentary
rocks of Michigan Basin
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Basal till-South Haven
Glacial moraines in SW Michigan
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Lateral moraine; Athabasca Glacier;
Alberta
Glaciers and Ice Sheets
Glacial landforms
•Esker
•Ridge deposited by
a river flowing in a
tunnel at the base of
a glacier
•Drumlin
•Streamlined hill
formed by squeezing
of soft sediment at
the base of the ice
Dahlen esker; eastern North Dakota
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Road cut through esker; southern Manitoba
Glaciers and Ice Sheets
• Periglacial landforms
– Tundra
– Permafrost
• Ground that is
perennially below the
freezing point of
water
– Ice wedges
– Patterned ground
• Produced by freeze-
thaw cycle
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Active Ice wedge (USGS)
Ice wedge cast
Relict ice wedge polygons-Wisconsin. Indicative of
past permafrost conditions.
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Differential thaw of permafrost (USGS)