Glaciers and Glaciation - The Changing Earth: Exploring Geology and Evolution - page 379

Stratifi ed drift in outwash plains and valley trains consists
of sand and gravel deposited by meltwater streams issu-
ing from glaciers. Ridges known as eskers, and conical
hills called kames are also composed of stratifi ed drift.
Major glacial intervals separated by tens or hundreds of
millions of years probably occur as a result of the chang-
ing positions of tectonic plates, which in turn cause
changes in oceanic and atmospheric circulation patterns.

Currently, the Milankovitch theory is widely accepted as
the explanation for glacial-interglacial intervals.
The reasons for short-term climatic changes, such as the
Little Ice Age, are not understood. Two proposed causes
are changes in the amount of solar energy received by
Earth and volcanism.

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Important Terms

abrasion (p. 367)
arête (p. 372)
basal slip (p. 361)
cirque (p. 369)
continental glacier (p. 360)
drumlin (p. 374)
end moraine (p. 373)
esker (p. 375)
fi ord (p. 369)
fi rn (p. 361)
glacial budget (p. 362)
glacial drift (p. 372)
glacial erratic (p.372)
glacial ice (p. 361)

glacial polish (p. 367)
glacial striations (p. 367)
glacial surge (p. 364)
glaciation (p. 360)
glacier (p. 359)
ground moraine (p. 373)
hanging valley (p. 369)
horn (p. 372)
ice cap (p. 360)
kame (p. 375)
lateral moraine (p. 374)
Little Ice Age (p. 358)
medial moraine (p. 374)
Milankovitch theory (p. 377)

outwash plain (p. 375)
plastic fl ow (p. 361)
recessional moraine (p. 373)
stratifi ed drift (p. 373)
terminal moraine (p. 374)
till (p. 372)
U-shaped glacial trough
(p. 367)
valley glacier (p. 359)
valley train (p. 375)
zone of accumulation (p. 362)
zone of wastage (p. 362)

Review Questions

1. The zone of accumulation on a glacier is
a. _____ the area where fi rn is converted
to glacial ice;
b. _____ where additions exceed losses;
c. _____ at a depth of about 40 meters;
d. _____ where most basal slip takes place;
e. _____ an erosional landform.
2. All sediment deposited directly by glacial ice is called
a. _____ varve;
b. _____ esker;
c. _____ outwash;
d. _____ till;
e. _____ kame.
3. Which one of the following is a feature caused by valley
glacier erosion?
a. _____ valley train;
b. _____ dropstone;
c. _____ terminal moraine;
d. _____ glacial recession;
e. _____ hanging valley.
4. Glaciers move mostly by
a. _____ plastic fl ow;
b. _____ surging;
c. _____ lateral compression;

d. _____ abrasion;
e. _____ glacial polish.
5. When freshly fallen snow compacts and partly melts
and refreezes, it forms granular ice known as
a. _____ drift;
b. _____ fi rn;
c. _____ cirque;
d. _____ drumlin;
e. _____ till.
6. If a glacier has a negative budget
a. _____ its terminus retreats toward the zone of
accumulation;
b. _____ its fi rn limit moves toward the glacier's terminus;
c. _____ it fl ows much more rapidly for a short time;
d. _____ its zone of wastage disappears;
e. _____ it advances and modifi es previously deposited
moraines.
7. The only two areas where continental glaciers are
present today are
a. _____ Canada and Alaska;
b. _____ Montana and Wyoming;
c. _____ Greenland and Antarctica;
d. _____ Scandinavia and Siberia;
e. _____ Iceland and Baffi n Island.