Glaciers and Glaciation
Glaciers and Glacial Features
• Glaciers – a mass of ice that moves over the land
under its own weight and shapes the land
– Excellent indicator for global climate conditions (warm or
cool). Not be developed in a single winter
• Glacier Formation
– Heat from the sun is generally constant so,
– Climate factors may influence the global temperature
budget
• Global cooling – ice will accumulate and build ice sheets and
glaciers
• Global warming – ice sheet retreat and glaciers get smaller
• Factors that change climate include – composition of the
atmosphere, pollution or particles suspended in the atmosphere,
abnormal heat retention (or loss) from the oceans
Glaciers
• Glaciers are parts of two basic cycles
• Hydrologic cycle
• Rock cycle
• Glacier – a thick mass of ice that originates
on land from the accumulation,
compaction, and recrystallization of snow
And cover about 10% of Earth’s land surface
Glaciers as a water source
• Important freshwater source
– Approximately 75 % of fresh water is stored as glacial ice
• Glacial meltwater may be the principal source of
summer streamflow in the regions having glaciers
• Overall volume of glacial ice can be manipulated
– Cloud seeding activities in glacial areas may cause
accumulation of increased amounts of ice
– Dusting glaciers with black coal may cause an increase melt
of glacial ice to occur
Glaciers
• Types of glaciers
• Valley (alpine) glacier
– Exists in mountainous areas
– Flows down a valley from an accumulation
center at its head
• Ice sheet
– Exists on a larger scale than valley glaciers
– Two major ice sheets on Earth are over
Greenland and Antarctica
– Often called continental ice sheets
– Ice flows out in all directions from one or more
snow accumulation centers
Present-day ice sheets
Greenland
Glaciers
• Other types of glaciers
– Ice caps
– Outlet glaciers
– Piedmont glaciers
Ice Cap
Piedmont glacier
Glaciers
• What if the ice on Earth melted?
• Slightly more than 2 percent of the world’s
water is tied up in glaciers
• Antarctic ice sheet
– Eighty percent of the world’s ice
– Nearly two-thirds of Earth’s fresh water
– Covers almost one and one-half times the area of
the United States
– If melted, sea level would rise 60 to 70 meters
Formation of glacial ice
• Glaciers form in areas where more snow falls
in winter than melts during the summer
• Steps in the formation of glacial ice
• Air infiltrates snow
• Snowflakes become smaller, thicker, and more
spherical
• Air is forced out
• Snow is recrystallized into a much denser mass
of small grains called firn
• Once the thickness of the ice and snow
exceeds 50 meters, firn fuses into a solid mass
of interlocking ice crystals – glacial ice
The transformation of
snow to glacial ice
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Movement of glacial ice
• Movement is referred to as flow
• Two basic types
– Plastic flow
» Occurs within the ice
» Under pressure, ice behaves as a plastic
material
– Basal slip
» Entire ice mass slipping along the ground
» Most glaciers are thought to move by this
process
• Zone of fracture
– Occurs in the uppermost 50 meters
– Tension causes crevasses to form in brittle ice
• Rates of glacial movement
•
•
•
•
Average velocities vary considerably from one glacier to another
From imperceptible to several meters/year
Byrd Glacier – 2m/day
Some move in surges –active advances
Glaciers move by basal
sliding and internal flow
Glacial erosion
• Glaciers are capable of great erosion and
sediment transport
• Glaciers erode the land primarily in two ways
• Plucking – lifting of rocks
• Abrasion
– Rocks within the ice acting like sandpaper to
smooth and polish the surface below
Figure 9.10 A and B
• Glacial erosion
• Glacial abrasion produces
– Rock flour (pulverized rock)
– Glacial striations (grooves in the bedrock)
Figure 11.12
Figure 11.13
Figure 11.14
The Matterhorn in
the Swiss Alps
Figure 11.15
Glacial deposits
• Glacial “drift” – refers to all sediments of
glacial origin
• Types of glacial drift
– Till – material that is deposited directly by the ice
– Stratified drift – sediments laid down by glacial
meltwater
Glacial till is typically unstratified
and unsorted
Glacial deposits
• Landforms made of till
• Moraines
– Layers or ridges of till
• Moraines produced by alpine glaciers
– Lateral moraine
– Medial moraine
• Other types of moraines
– End moraine – terminal or recessional
– Ground moraine
Figure 11.20
Glacial depositional features
Glacial deposits
• Landforms made of till
• Drumlins
– Smooth, elongated, parallel hills
– Steep side faces the direction from which the ice
advanced
– Occur in clusters called drumlin fields
– Formation not fully understood
A drumlin in upstate New York
Glacial deposits
• Landforms made of stratified drift
• Outwash plains (with ice sheets) and valley
trains (when in a valley)
– Broad, ramp-like surface composed of stratified
drift deposited by meltwater leaving a glacier
– Located adjacent to the downstream edge of most
end moraines
– Often pockmarked with depressions called kettles
• Landforms made of stratified drift
• Ice-contact deposits
– Deposited by meltwater flowing over, within, and
at the base of motionless ice
– Features include
» Kames
» Eskers
Glaciers of the past
• Ice Age
• The Ice Age began between 2 million and 3
million years ago, ended about 10,000yr ago
• Most of the major glacial stages occurred
during a division of geologic time called the
Pleistocene epoch
Maximum extent of ice
during the Ice Age
End moraines of the Wisconsinian
and Illinoian
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Glaciers of the past
• Indirect effects of Ice Age glaciers
• Forced migration of animals and plants
• Changed stream courses
• Rebounding upward of the crust in former
centers of ice accumulation
• Worldwide change in sea level
• Climatic changes
Coastline changes due
to glaciation
Changes in
river courses
Today
Prior to Ice age
Figure 11.26
Pluvial Lakes
Great Salt Lake
remains
“Salt Flats”
Causes of glaciation
• Some proposed causes of glaciation
• Volcanic eruptions……not long enough effects
• Change in solar output…….11 yr cycle not enough
• Plate tectonics
– Continents were arranged differently in the past
– Changes in oceanic circulation
– Would only account for Pleistocene glaciation
• Variations in Earth’s orbit….better supported
– The Milankovitch model
» based on:
1. Shape
(eccentricity) of
Earth’s orbit
varies
2. Angle of Earth’s
axis (obliquity)
changes
3. Earth’s axis
wobbles
(precession)
Support for Milankovitch model:
• Analysis of deep sea organisms sensitive to
climate variations used to establish chronology of
temperature change over past 500,000 years.(J.D.
Hays et al)
• This analysis compared to astronomical
calculation of eccentricity, obliquity and
precession did find a correlation.
• Other factors affecting climate change?
– Study of air trapped in ice from Antarctica indicate
less CO2 and methane at that time
– Also weaker warm currents towards poles at the time
Vanishing Glaciers Muir glacier, Alaska 1902-2005
Vanishing Glaciers Caroll Glacier, Alaska
1906 - 2004
Grinnell Glacier, Glacier National Park
1938,1981,1998,2006
Mt. Kilimanjaro 19932000