Ice Sheets and Glaciers

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Ice Sheets and Glaciers
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Glaciations Through Time
Gowganda GlaciationLate Precambrian
Glaciation
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Early Paleozoic (Saharan Glaciation) Late
Paleozoic (Gondwana Glaciation)
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The Late Cenozoic Bi-Polar GlaciationNorthern
Hemisphere Ice Sheets are climate
sensitiveAntarctic Ice Sheet is a polar ice sheet
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Antarctic Ice Sheet Drainage
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Ice Sheet Drainage EAIS is a terrestrial ice
sheet1. Average flow rate 5-10 metersper
year2. Steep (equilibrium profile)WAIS is a
marine ice sheet1. Drainage is mainly
throughice streams at rates of a fewhundred
meters per year2. Unstable profile
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Mountain peak is all that extends above The East
Antarctic Sheet
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Aerial view of West Antarctic Ice Sheet showing
gentle surface slope and flat-topped ice shelf
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left-aerial view of Ross Ice Shelf right - aerial
view of calving wall of ice shelf
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Where ice drainage converges toward the coast,
rapidly flowing ice streams occur
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Glacial Environments
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Glacial Erosion produces polished surfaceswith
striations (right) and chatter marks
(below)Abrasion (slow sand papering action)and
plucking (removal of large rock fragments)occurs
at a small scale
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Glacial erosion produces largescale landforms
such as rouchemoutonees and bedrock drumlins
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Glaciers produce U-shaped valleys on land (top)
and and u-shaped troughs where they advance onto
the sea floor (below)
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Where ice sheets advance onto the sea floor they
produce erosional surfaces (unconformities) that
are tens to hundreds of meters deep and typically
slope in a landward direction
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Basal Debris Zones
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Ice streams shear and deform the beds they
over-ride to create deforming beds. Once this
happens, the ice stream slides across the
deforming bed and the rate of flow of the ice
stream increases due to basal sliding. The
geomorphic product of basal sliding are
mega-scale glacial lineations that are tens of
meters high and tens of kilometers in length
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View of outcrop of till. Note the progradation
from left to right. The term till delta is used
for this type of deposit
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Tills are characterized by a lackof
stratifications and sorting
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Another characteristic of tills is their uniform
grain size and mineralogy within individual
units. The uniform mineralogy is manifest as
uniform magnetic susceptibility ( a measure of
the concentration of magnetic minerals in the
till)
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The rock clasts within tills tend to be angular
and have jagged corners (facets (lower left).
Grains of all sizes have striations and sand
grains have concoidal fratctures (lower right)
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Studies of till composition have shown that rock
and mineral composition varies little along ice
flow lines. This has been used to conduct till
provenance studies and reconstruct past ice
drainage.
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Moraines-ridges formed at the terminus and
margins of glaciers
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Moraines also form on the sea floor where ice
sheets were once grounded
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Ice Rafting (debris transport by icebergs)
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Glaciomarine Sediments are a mixture of
ice-rafted material and marine sediment.
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Glaciomarine sediments may be stratified and
sorted, unlike tills
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The equilibrium line of a glacier separates the
zone where accumulation exceeds ablation from the
zone where ablation exceeds accumulationss. As
the climate changes, the equilibrium line will
shift up or down glacier
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Polar glaciers (meaning that the ice rarely
melts) are characterized by clean ice whereas
temperate glaciers (where melting does occur, are
characterized by dirty ice and meltwater streams.

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Photo at top is from an Antarctic fjord showing
sediment-free water and photo at bottom is a
meltwater stream
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Temperate Glaciers are characterized by abundant
sediment, both in the ice and in meltwater
streams. This is because the equilibrium line of
the glacier is located far up the glacier.
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Glacial Lacustrine Environments