GEOLOGY 12
CHAPTER 17
GLACIERS
QUESTIONS FOR REVIEW
1.
ANSWERS
What proportion of the earth's fresh water is currently found as ice? Describe how
this water cycles through a glacier.
♦ About three-quarters of the earth's fresh water is now found in glaciers.
♦ Cycling Water Through a Glacier
2.
1.
It is added to the glacier as precipitation (usually snow).
2.
Over time and with continued precipitation, the snow is compacted into ice.
3.
When a sufficient mass has accumulated, the ice begins to flow.
4.
At the advancing edge of the glacier, ice loss occurs by evaporation, by
melting, or by calving of icebergs.
Describe three conditions that encourage glacier formation.
♦ Abundant snowfall is essential.
♦ The temperature must be cold enough year-round that the snow persists.
♦ A gentle slope for the snow to accumulate will also promote the development of a
glacial ice mass.
3.
What is the distinction between continental and alpine glaciers?
♦ The primary distinction between these two types of glaciers is one of size.
♦ The alpine glaciers are small, found in mountainous terrain, and usually confined
to a single valley.
♦ Continental glaciers are larger and cover a significant portion of a continent.
4.
What is rock flour, and how is it produced?
♦ ROCK FLOUR is very finely pulverized, silt-sized sediment produced as the
glacier and the rock fragments abrade the rock surfaces over which the glacier
flows.
♦ Rock flour is also very little altered, chemically or mineralogically, from the parent
rock composition.
5.
How does glacial till differ, in terms of sorting, from many water-laid sediments?
Why?
♦ Glacial till is usually much less well sorted.
♦ The maximum size of particle a stream can move is largely a function of its
velocity. As the velocity decreases, the largest particles are selectively dropped.
♦ A solid glacier moves all sizes of fragments together, independent of its velocity.
♦ Similarly, as the glacier melts, fragments of all sizes are deposited together.
6.
Describe the origin of hanging valleys and striations.
♦ HANGING VALLEYS form where small tributary glaciers join a larger glacier. The
smaller glaciers typically have less deep valleys. When the glaciers melt away, the
tributary valley floor ends at the main valley, high above the floor of the larger
valley.
♦ STRIATIONS are the fine parallel grooves cut by glaciers into the rocks over
which the glacier flows. These grooves are produced by other rocks frozen into
the base of the glacier.
7.
What is moraine? Distinguish among the following: ground moraine, terminal
moraine, and medial moraine.
♦ MORAINE is any landform made of till.
♦ GROUND MORAINE is a till sheet left by a retreating glacier; terminal moraine is
the end moraine (formed at the advancing edge of a glacier) that marks the
farthest extent of the ice.
♦ MEDIAL MORAINE is a moraine formed by the joining of two.
♦ LATERAL MORAINES where two glaciers join and begin to flow together.
8.
How do outwash deposits originate? What is an esker?
♦ OUTWASH DEPOSITS form when till is transported and redeposited by
meltwater.
♦ ESKERS form from meltwater streams flowing in and under the ice depositing
sediments along their icy channels; when the glacier melts, all that is left is the
sinuous ridge of sediment.
9.
Describe the annual depositional cycle of a glacial lake that gives rise to varves.
♦ In spring and summer, increased meltwater flow carries more sediment into the
lake. At the same time, microorganisms and algae grow in the lake above.
♦ In fall and winter, sedimentation decreases, and the organisms die and settle to
the bottom where they deposit an organic-rich layer over the inorganic sediment
layer.
10. Cite and briefly summarize any three proposed causes of ice ages. (Many answers
are possible.)
♦ Periods of intense VOLCANIC ACTIVITY may put so much dust into the air and
block so much sunlight that global cooling occurs and an ice age begins.
♦ Changes in TILT OF THE EARTH'S AXIS: if polar regions are tilted farther away
from the sun, and become colder, ice sheets may begin to accumulate there.
Geology 12
Chapter 17
Questions For Review
Page 2
♦ CONTINENTAL DRIFT: shifting continents may disrupt equator-to-pole ocean
currents that moderate polar temperatures. This would allow the poles to get
colder and so promote ice accumulation.
♦ Changes in SOLAR RADIATION: a decrease in solar energy output, such as we
see periodically during the modern sunspot cycle, could reduce solar heating of
the earth and initiate an ice age.
11. What is the greenhouse effect? Why is it a subject of increasing concern in modern
times?
♦ The term "GREENHOUSE EFFECT" refers to atmospheric heating as a
consequence of the trapping of infrared radiation by certain molecules, especially
CO2.
♦ Intensive burning of fossil fuels over the last century has caused measurable
increases in atmospheric CO2, with no end in sight.
♦ It is feared that significant Greenhouse Effect heating will therefore occur, melting
remaining ice sheets, raising global sea levels, and flooding low-lying coastal
regions.
Geology 12
Chapter 17
Questions For Review
Page 3