4.10
Glaciers: Rivers of Ice
Glaciers, masses of ice and snow built up over thousands
of years, occur in the high altitudes of mountains (alpine
glaciers), as shown in Figure 1, and on the lands near Earth’s
poles (continental glaciers). The lower layers of glaciers are
turned into clear ice because of the weight of the snow above.
This great weight also causes alpine glaciers to ooze slowly
down the mountains.
A continental glacier covers the entire continent of
Antarctica. Another covers most of the island of Greenland,
an area of 1.8 million square kilometres. At its thickest point,
Greenland’s continental glacier extends 2700 m from top to
bottom. (See Figure 2.) Continental glaciers are usually thickest
at the centre and slowly flow out in all directions from there.
Cold air flows off continental glaciers, cooling the
surrounding area and helping to form strong winds
known as the polar easterlies. Because these
winds are so cold, they provide little
precipitation. Antarctica, for example,
is a true desert with the harshest
conditions on Earth: average
temperatures around –50°C and
an annual precipitation of less
than 3 cm.
The large sheet of ice on
the Arctic Ocean, called the
polar icecap, is not a glacier
because it lies over water, not
land. Although conditions
at the North Pole are less
severe than those in
Antarctica, this icecap
produces similar weather
effects to those caused
by continental glaciers.
Figure 3 illustrates arctic
pack ice, floating ice that has
been driven together to form
a single mass.
Figure 1
Supervised hikes
attract many tourists to
Rocky Mountain glaciers.
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Unit 4
Greenland
Glacier
2700 m
CN
Tower
553 m
Figure 2
Greenland’s continental glacier is almost
equal in height to five CN Towers.
Figure 3
Spring conditions cause the
ice to break up into large
ice floes.
Glaciers store huge amounts
of fresh water as snow and ice.
Some of this water, especially at
the melting edges of the glacier,
rejoins the water cycle fairly
quickly as a valuable source of
liquid water. When the glacier
finally oozes its way to the ocean,
icebergs break off into the water.
Icebergs can threaten shipping
lanes and offshore oil rigs. The
most famous shipping disaster
occurred in 1912 when the
Titanic struck an iceberg and
sank. However, icebergs may have
benefits. Since they consist of
fresh water, people may start
towing icebergs to places where
drinking water is needed.
Glaciers of Old
The largest glaciers of today are small compared with the
glaciers of the last major Ice Age. Beginning about 2 million
years ago, ice sheets spread over most of North America
(Figure 4) and Eurasia. When the ice began to melt
at the end of the last Ice Age, sea levels rose.
Land that was pressed down by the immense
weight of the ice continues to move upwards, or
rebound. The remains of the last Ice Age include
the Greenland and Antarctic ice sheets. Today people are
concerned about global warming and fear that coastal lands
will be covered with water if polar ice melts quickly.
a 18 000 years ago
b 8000 years ago
Understanding Concepts
1. Describe three effects glaciers
have on the environment.
Exploring
2. Design a simulation of how a
glacier turns snow into ice.
3. Research print and electronic
resources to explore one of the
8C following topics. Be prepared to
present your findings in an
interesting way. End your
presentation with three new
questions you thought of during
your research.
4A
(a) During the last Ice Age, the
ice receded due to changing
climate. How might global
warming affect glaciers and
the world in the future?
(b) Explain why fossils of marine
animals are found in places
where no oceans exist. (See
Figure 5.) Provide specific
references to glaciation.
Northwest
Territories
•
Fort McMurray
British
Columbia
Alberta
Figure 5
Why were fossils of this prehistoric
marine reptile found hundreds of
kilometres from any ocean?
(c) Draw at least 2 maps like
those in Figure 4, showing
the position of ice today
and at one or more other
time periods.
Reflecting
Figure 4
Since 18 000 years ago, the ice covering
North America has gradually melted.
SKILLS HANDBOOK: 4A Research Skills 8C Multimedia Presentations
4. Describe, using specific examples,
how this section on glaciers is
related to the water cycle.
Water Systems
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