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Introduction
The Kinds of Glaciers
™Glaciers are masses of ice
which move over land by
plastic flow and basal slip.
By definition glaciers are moving bodies of ice on land,
that flows downslope or outward from an area of
accumulation.
™Glaciers presently contain
2.15% of all water on Earth
and cover about 10% of the
land surface.
Sea ice and icebergs are nothing more than frozen
seawater and are not glaciers because they do not
form on land.
Fig. 14.2, p. 359
The Kinds of Glaciers
Fig. 14.4b p. 361
Valley Glaciers
™ Valley glaciers are also called alpine glaciers and
mountain glaciers
™Valley Glaciers
™Long, narrow tongues of
ice
™Typically much smaller
than continental glaciers
™Flow from higher to
lower elevations
™Confined within
mountain valleys.
™Create spectacular
scenery!
™ Valley glaciers that flow into the
sea are called tidewater glaciers.
Fig. 14.1b, p. 358
The Kinds of Glaciers
Fig. 14.2, p. 359
The Kinds of Glaciers
™Continental Glaciers
Continental glaciers flow outward in all
directions from a zone of accumulation
Fig. 14.3 a, p. 360
™Ice Caps
™ Huge - cover vast
areas.
areas
™ Often develop large
ice shelves where
they flow outward
into the sea.
Fig. 14.3 a-b, p. 360
™ Similar to
continental glaciers
but much smaller
smaller.
™Some develop from
valley glaciers when
they grow over the
top of a divide.
Fig. 14.3 c, p. 360
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Moving Bodies of Ice on
Land
Glaciers
Moving Bodies of Ice on Land
™ How Do Glaciers Originate and Move?
™Glaciers—Part of the Hydrologic Cycle
Glaciers form when winter snowfall exceeds summer
melt and snow accumulates yearly.
™ Ice is a crystalline solid. Fresh snowflakes are about
80% air.
™Glaciers are a reservoir in the
hydrologic cycle where water is
stored for long periods as it
moves from the oceans to land
and back to the oceans.
™As th
™A
the snow accumulates
l t
it thaws and refreezes,
becoming a granular type
of ice called firn.
™When firn is buried and
and recrystallized, it is
metamorphosed to glacial
ice and will flow under its
own weight.
Fig. 14.4a, p. 361
Geo-Insight 8., p. 371
Glaciers
Moving Bodies of Ice on Land
Glaciers
Moving Bodies of Ice on Land
™How Do Glaciers Originate and Move?
™Glaciers move thru Basal Slip and Plastic Flow
™If a slope is present glaciers
may slide over their
underlying surface,
surface a
phenomenon called basal
slip
™Most of their movement is
accomplished by plastic
flow, a type of deformation
that takes place in response
to stress.
™Distribution of Glaciers
™Glaciers exist only where there is
™Sufficient precipitation in the form of snow
™Temperatures are low enough that they do not
melt
™ These conditions prevail in
™High mountains (some even near the equator) or
™High latitudes (such as in Alaska, the Canadian
Arctic islands, Greenland, and Antarctica.)
Fig. 14.5, p. 362
The Glacial Budget
Accumulation and Wastage
The Glacial Budget
Accumulation and Wastage
™ Glacial budget - A glacier's behavior depends on the
balance between accumulation and wastage (melting).
™ Glacial budget - A glacier's behavior depends on the
balance between accumulation and wastage (melting).
™The upper part of the
glacier, where the snow
cover is year-round is the
zone of accumulation.
™The lower part, where
losses exceed gains is the
zone of wastage.
™The line separating the
two is the firn limit. It
shifts each year.
™Glaciers having a
balanced budget have a
stationar terminus.
stationary
termin s The
firn limit changes very
little from year to year.
™Positive and negative
budgets result in advance
and retreat of the
terminus, respectively.
Fig. 14.7 a-b, p. 366
Fig. 14.7 a-b, p. 366
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The Glacial Budget
Accumulation and Wastage
The Glacial Budget
Accumulation and Wastage
™ Glacial budget - A glacier's behavior depends on the
balance between accumulation and wastage (melting).
™How Fast Do Glaciers Move?
™The rate of glacial
movement depends on
the slope
slope, discharge and
season.
™In general, valley
glaciers move more
rapidly than do
continental glaciers
™A valley glacier with a
balanced budget will
deposit a terminal
moraine at its base.
™If it has a negative
budget a recessional
moraine may develop.
Fig. 14.7 a-b, p. 366
The Glacial Budget
Accumulation and Wastage
Fig. 14.5, p. 367
The Glacial Budget
Accumulation and Wastage
™Glacial Surges - During a glacial surge, accelerated
flow into a glacier causes its terminus to advance rapidly
™ Its surface breaks into a maze of
crevasses.
™ Theories for the cause of surges:
™ 1. Water-saturated sediment below a glacier
allows it to slide
™ 2. A glacier’s slope increases due to
thickening in the zone of accumulation and
thinning in the zone of wastage.
Fig. 14.6, p. 363
Erosion and Transport by Glaciers
Erosion and Transport by Glaciers
™ Glaciers effectively erode and transport significant
amounts of sediments because they are moving solids.
Glaciers…
™Push or bulldoze loose materials in their paths
™Erode by abrasion - that is, the movement of
sediment-laden ice over rock surfaces
™Erode by plucking when ice freezes in or around
bedrock projections and pulls them loose.
™They are very effective in
eroding soil and
unconsolidated
nconsolidated sediment
sediment.
™Glaciers deposit huge
amounts of sediment of all
grain sizes, from boulders
the size of a house down to
rock flour.
Fig. 14.11, p. 369
Fig. 14.9, p. 368
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Erosion and Transport
by Glaciers
Erosion and Transport by Glaciers
™Erosion by Valley Glaciers
Glaciers…
™ Valley glaciers carve angular peaks and deep valleys
™Polish rocks as they grind them into a fine powder
called rock flour.
™Abrasion also results in glacial striations –
scratches
t h made
d b
by rocks
k scraping
i against
i t one
another as the glacier moves
™U-Shaped Glacial Troughs
™When mountain valleys
are eroded
d db
by glaciers
l i
they are deepened and
widened so that they have
flat or gently rounded (Ushaped) valley floors and
near-vertical valley walls.
Fig. 14.10, p. 368
Erosion and Transport by Glaciers
Fig. 14.12 b, p. 369
Erosion and Transport by Glaciers
™Erosion by Valley Glaciers
™A fiord forms when sea level rises and fills a Ushaped glacial valley with sea water.
™Erosion by Valley Glaciers
Hanging Valleys
™ Create some of the world’s most spectacular waterfalls
™ Form when a former glacial tributary
reaches the main valley
U-Shaped
Glacial Troughs
Fig. 14.12c, p. 369
Geo-Insight 8., p. 371
Geo-inSight 3-5, p. 370
Erosion and Transport
by Glaciers
Erosion and Transport
by Glaciers
™Erosion by Valley Glaciers
™Erosion by Valley Glaciers
™Arêtes and Horns
™Cirques
Fig. 14.12c, p. 369
™At the upper end of the
glacial trough, a scoopshaped depression, or
cirque, eroded into a
mountain side marks the
place where a glacier
formed and moved out
into a trough.
Fig. 14.16a, p. 375
™ Both are landforms
generated by valley glacier
erosion.
™ An
A arête
êt is
i a serrated
t d ridge
id
between U-shaped glacial
troughs or between adjacent
cirques
™ A horn is a pyramid-shaped
peak left when headword
erosion takes place by at
least three glaciers in the
same peak.
Geo-inSight 10., p. 370
Fig. 14.12c, p. 369
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Erosion and Transport by Glaciers
Deposits of Glaciers
™Continental Glaciers
and Erosional Landforms
™Glacial Drift – a general term for all glacial
deposits
™ Areas eroded by continental glaciers
™ Are smooth and rounded, ice-scoured plains
™ Create deranged drainages with swamps and lakes
™ Exhibit large areas of polished and striated bedrock
™ Erratics – huge boulders derived from distant source
areas, transported to their current location by
g
glaciers
Fig. 14.13, p. 372
Deposits of Glaciers
Fig. 14.14 a-b, p. 373
Deposits of Glaciers
™Glacial Drift – a general term for all glacial
™Landforms Composed
deposits
™ Two types of drift
™ 1. Till – sediments deposited directly by glacial ice.
Poorly sorted.
™ 2. Stratified drift – sediments deposited by running
water, usually in braided streams. Well-sorted.
of Till
™ End moraines – Crescent shaped deposits of till
that form near the terminus of the glacier.
™ Form a pile of rubble at the front of the glacier
Fig. 14.15b, p. 374
Fig. 14.18a, p. 377
Deposits of Glaciers
Fig. 14.15, p. 374
Deposits of Glaciers
™Landforms Composed of Till
™Landforms Composed
of Till
™ Recessional moraine.
™ Suppose that a glacier reaches its maximum extent
and has a balanced budget.
™Accordingly it deposits a terminal moraine.
™ If it then has a negative budget,
™Its terminus retreats and perhaps becomes stabilized once
again if its budget is balanced
™In this case another end moraine is deposited but it is
called a recessional moraine.
™ Lateral and Medial Moraines –
Ridge shaped deposits of till that
form within the glacier
glacier.
™ Created by plucking rock from
the valley walls
™ Lateral moraines form along the
sides of the glacier
™ Medial moraines form where two
lateral moraines meet
Fig. 14.16 b, p. 375
Fig. 14.7b, p. 366
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Deposits of Glaciers
Deposits of Glaciers
™Landforms Composed of Stratified Drift
™Landforms Composed of Till
™ Sediments deposited by glacial meltwater. Well sorted.
™Drumlins
™ Streamlined hills of till shaped by continental
glaciers or by glacial meltwater floods. Form
drumlin fields, with 100’s of drumlins present.
™ Outwash Plains – vast blankets of sediment, usually
sand and gravel, that form in front of the glacier as it
melts
™ Valley Trains – deposits of braided streams that form
long, narrow deposits of stratified drift.
Fig. 14.17, p. 376
Fig. 14.18a, p. 377
Fig. 14.17, p. 376
Deposits of Glaciers
Deposits of Glaciers
™Landforms Composed of Stratified Drift
™Deposits in Glacial Lakes
™ Kames – conical hills created when a stream deposits
sediment in a depression on the glacier’s surface.
™The most distinctive deposits in
glacial lakes are varves
™ Eskers – snake-like deposits from sub-glacial streams
™Varves consist of couplets of
dark and light, laminated, finegrained sediment
sediment.
™The dark layers form during the
winter when small particles of clay
and organic matter are deposited.
™The light layers are made up of silt
and clay that form during the
warmer months.
Fig. 14.17, p. 376
Fig. 14.19, p. 377
What Causes Ice Ages?
™The age of a glacial lake may be
determined by counting the
layers.
Fig. 14.20a, p. 378
What Causes Ice Ages?
™ The Milankovitch Theory
™ An explanation for the onset of the
glacial episodes
™Short-Term Climatic Events
™ Milankovitch cycles can be measured in 10’s of
thousands of years. They are too long to explain
events like the Little Ice Age that lasted just a few
h d d off years
hundreds
™ Milankovitch claimed that
irregularities in Earth’s rotation and
orbit bring about complex climatic
changes that provide the triggering
mechanism for glacial episodes.
™ Several hypotheses have been proposed
™ Variations in solar energy due to solar flares or
interstellar dust
™ Volcanic eruptions are known to cause short term
climate change. A series of large eruptions could
produce a prolonged event.
™ The 3 primary factors are
™orbital eccentricity
™changes in axial tilt
™precession of the equinoxes
Fig. 14.21, p. 378
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