Title Page Photo
“Glaciers are almost gone from Glacier National Park”
— Donella Meadows (Brainyquote.com)
Glacial Modification of Terrain
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The Impact of Glaciers on the Landscape
Glaciations Past and Present
Types of Glaciers
Glacier Formation and Movement
The Effects of Glaciers
Continental Ice Sheets
Mountain Glaciers
Periglacial Environment
Causes of the Pleistocene
 The Impact of Glaciers on the Landscape
• Extent of Glaciations
– Glacial ice coverage of the land surface
• Past –  1/3 (i.e. maximum extent)
• Today –  1/10
• Slow moving “rivers of ice”
• Direct Impacts
– Glacial topography and meltwater are the bases
for many of the world’s lakes and river channels
e.g. the Great Lakes
– Glaciers sculpted the awesome alpine vistas
(e.g. in Switzerland)
– Glacial deposits are parent material for soils
– Glaciers still cover sizeable areas of Earth’s land
surface
 Glaciations Past and Present
• Pleistocene Glaciations
Animation
– Time period
1. End of the Last Ice Age
2. Isostasy
• Roughly the last 2 million years
– End of Pleistocene Epoch
• ca. 10,000 yrs. ago
• Holocene epoch then began (interglacial/post-glacial)
• And we are still in this Holocene period
– Extent (shown in Animation and next slides)
- Fig. 19-1a. The maximum extent of Pleistocene glaciations worldwide.
- Fig. 19-1b. The maximum extent of Pleistocene
glaciations in North America.
- Fig. 19-1c. The maximum extent of Pleistocene
glaciations in Western Eurasia.
Indirect Impacts of Pleistocene Glaciers
– Periglacial processes and features they created
• ‘Peri’ means ‘outside’ the glacial zone. The effects here are mainly
by their melt-waters. E.g. glacial outwash plains
• Also, frost weathering, solifluction, etc
• Other periglacial features (treated later in this chapter)
Sea-level changes:
•When glaciers advanced (i.e. more ice), sea
level dropped. It was 130 m (430 ft.), which is
lower than it is today. And when glaciers
retreated (or melted), sea level rose.
•Also, relatively low evaporation rates added to
surplus water. Many of the large dry lake beds
today were full. E.g. Lake Bonneville, Utah.
The parent of the Great Salt Lake. Fig. 19-2
– Crustal depression
• Enormous weight of ice sheets
• Isostatic adjustment, crust is rebounding where glacial ice
existed (isostacy).
– Response to weight loss
– Fig. 13-21.
• Contemporary Glaciation (today)
– Two-thirds of the world’s fresh water is frozen
– Antarctic Ice Cap
• West Antarctica
• East Antarctica
- Fig. 19-4
– Greenland Ice Cap
– Photo Source: NASA (Image retrieved using
NASA’S World Wind software)
– North American Glaciers
– Fig. 19-6.
 Types of Glaciers
• 1) Continental Ice Sheets
– Found in non-mountainous
areas
– E.g. Antarctica and
Greenland Ice Sheets where
you have:
• Outlet glaciers
• Ice shelves
• Iceberg formation
– Fig. 19-7, pg 561.
Read caption.
• 2) Mountain Glaciers
– A) Highland Icefields (accumulates in unconfined sheets,
quite broad)
– Fig. 19-8. Icefield with a valley glacier and a piedmont glacier
as outlets (looks like an ‘icy alluvial fan’).
– B) Alpine Glacier (develops high up as ‘individual glaciers’)
– Cirques are the “bowls” they originate in
– Fig. 19-9. Three types of alpine glaciers: cirque, valley,
and piedmont.
– Fig. 19-10. Tributary alpine glaciers have joined to form
a very large glacier in foreground.
 Glacier Formation and Movement
• Changing snow to ice
– Compression and Coalescence
– Fig. 19-11.
– Zones of net accumulation and net ablation
– Fig. 19-12, see caption, pg 563
– mass (ice) balance
• ice inputs (zone of accumulation) vs. ice outputs
(zone of ablation)
• 3 conditions and landform development
– Inputs > outputs – advancing glacier 
till plain
end moraine
– inputs = outputs – stationary glacier 
– Inputs < outputs – retreating glacier 
 The Effects of Glaciers
Animation
(Glacial Processes)
• Erosion by Glaciers
– Glacial Plucking
Meltwater freezes
In sub-glacial rock
– Glacial Abrasion
– Fig. 19-14a. Grooves and striations caused by glacial
abrasion near Cuzco, Peru.
• Subglacial meltwater transport
– Meltwater from top of ice flows into crevasses and tubes and
ends up beneath glacier.
– Subglacial streams form, they carry debris beneath the ice
– Fig. 19-15. Meltwater stream flowing over the surface
of a glacier.
• Deposition by Glaciers
– Till is debris deposited directly by ice
• Unstorted/unstratified drift; heterogeneous collection of
debris of all sizes, which could range in size from
boulders to glacial flour.
– Fig. 19-16. Unsorted
glacial till.
– Fig. 19-17. Glacial erratic, example of till. This is a huge
boulder resting on a completely different type of bedrock,
and was brought by glaciers.
– Glaciofluvial deposits – debris deposited by melt
water
• Stratified drift (layered deposits)
– Photo Source: Pennsylvania Geological Survey
(http://www.dcnr.state.pa.us/topogeo/photogallery/)
 Continental Ice Sheets
• Development and Flow
– Origin of Pleistocene Ice Sheets
• Northern Hemisphere: Subpolar and midlatitude locations
• Antarctica
• Erosion by Ice Sheets
– Ice Excavations (extensive plucking action)
• Hudson Bay basin
• Great Lakes basins
• Finger Lakes
– Roche Moutonnée
– Fig. 19-19.
– Fig. 19-20. Lembert Dome, a roche moutonnée.
– Can you tell which direction the glacier moved from?
• Deposition by Ice Sheets
– Kettle
– Fig. 19-24. The formation of kettles.
– Drumlin
– Fig. 19-25. Drumlin west of Rochester, NY.
– Eskers
(glaciofluvial
debris/ gravel)
– Fig. 19-26. Eskers in eastern
Canada.
– Lakes
• Deranged
drainage
– Fig. 19-28. Lakes north of Ohio and Missouri rivers.
– Summary diagram of deposits associated with icesheets
• Fig. 19-21a and 21b. Glacier-deposited and glaciofluvially
deposited features of a landscape.
 Mountain Glaciers
• Development: long-term, high-elevation snowfall, above
the equilibrium line
• Example of Highland Icefield and valley glaciers (below)
– Fig. 19-29. Mt. Rainier, WA. Highland icefields with
tongues of valley glaciers radiating from the central field.
• Erosion by Mountain Glaciers
– Erosion dominates upper portion of the valley
- Fig. 19-33c
• Development of the erosional landscape
– Fig. 19-33a, b, c
– Cirque
• Upper end (head) of a
glaciated valley.
• The signature feature of
alpine glacial topography
– Fig. 19-31. Small
remnant glacier on the
north side of Wheeler
Peak in Nevada’s Great
Basin National Park.
– Fig. 19-32. Development of a cirque at the head of a
valley glacier.
– Fig. 19-36. Three small cirques on Mount Nebo in
Central Utah. The cirque glaciers never grew out
of their basins.
– Col
– Fig. 19-34. Col in a glaciated section of the Front
Range in north-central Colorado.
– Horn
– Fig. 19-35. Mount Aspiring, a prominent horn in
the Southern Alps of New Zealand.
- Glacial trough
– Fig. 19-38. Hollyford Valley, a glacial trough and
stairway in South Island, New Zealand.
– Fig. 19-39. Longitudinal cross section of a glacial trough
showing sequence of glacial steps (glacial stairway).
– Hanging Valley and Waterfall
– Fig. 19-40. Bridalveil Creek, occupies a hanging valley.
• Deposition by Mountain Glaciers
– Moraines (principal features)
– Fig. 19-41.
– Lateral moraine and nearby features
– Fig. 19-42
– Fig. 19-43. Emerald Bay, on Lake Tahoe. Two lateral
moraines almost close off the bay from the rest of the lake.
– Medial moraine
– Fig. 19-44. Dark strip of debris running down the middle
of the glacier is a medial moraine.
– End (terminal) moraine
• Nellie Juan Glacier and terminal moraine, Prince William Sound, Alaska.
(Source: U.S.G.S.: http://pubs.usgs.gov/of/2004/1216/m/m.html)
 The Periglacial Environment
• Periglacial – ‘perimeter of glaciation’
– 20% of world’s land area
• High latitudes and high elevations
– Usually areas covered by ice during Pleistocene epoch
– Non-glacial landscape features
• Permafrost (Chapter 9)
• Patterned ground
– Fig. 19-45. Polygonal ground patterns, near Prudhoe Bay, Alaska.
• Proglacial lakes
– Channeled scablands of Washington formed by periodic
discharges from an ice sheet-dammed Lake Missoula, a proglacial lake during the Pleistocene epoch.
-Fig. 19-46.
 Causes of the Pleistocene
• Explanations:
– Cyclical variation in Earth-Sun relations
• Seem to explain cycles of glaciations and deglaciations involving
tens of thousands to hundreds of thousands of years (Chapter 8).
• Shorter cycles are more difficult to explain.
– Fig. 19-47. Global temperature fluctuations. Many climate
scientists theorize that very long-term climate cycles are
controlled by cyclical changes in Earth-Sun relations.
– Other possible factors
• Variability of solar output
• Variations in amount of atmospheric CO2
• Changes in position of continents, configuration of ocean basins
and ocean circulation patterns
• Changes in atmospheric circulation due to increased elevation
of continental mass after a period of tectonic upheaval
• Reductions in insolation due to volcanic eruptions
• Are We Still in an Ice Age?
– Is our climate merely an interglacial warming period?
– If we are in an interglacial period, will human-induced
global warming slow down the return of another glacial
period?