Geoscience Reference
In-Depth Information
Glaciers in the Cascade Mountains
Although alpine glaciers are now rare in the contiguous United
States, a few nice ones can still be found in the Cascade
Mountains in the Pacific Northwest. The best developed of these
glaciers occur on the flanks of the large volcanoes in the range,
such as Mount Rainier and Glacier Peak. In order to explore
these ice masses more thoroughly, go to the
Geo Media Library
and select
Glaciers in the Cascade Mountains
. After you com-
plete the interactivity, answer the questions at the end to test
your understanding of Cascade glaciers.
into the ocean where they become
icebergs
. Such an iceberg,
of course, was involved in the tragic sinking of the
Titanic
in
1912.
In addition to ice caps and ice fields, another source area
for an alpine glacier is a
cirque
, which is a small, bowl-like
depression on a mountain flank formed by glacial erosion.
A good example of an environment where numerous cirque
glaciers have formed is the Cascade Mountains in the Pacific
Northwest. Recall from Chapter 7 that this region receives
abundant orographic precipitation from moisture-laden air
flowing off the Pacific Ocean to the west. This precipitation is
especially high on the numerous volcanoes that arc along the
range. Given that the peaks of the volcanoes are usually greater
than 3000 m (9800 ft) in elevation, summer temperatures near
the mountain crests are typically very cool.
Figure 17.11a shows the effect that these cool tempera-
tures have on snow cover. Note how much snow remains on
the flanks of Mount Hood in Oregon even during late summer.
Such snow cover is the foundation for several cirque glaciers on
this mountain, as well as on other volcanoes in the range. On
Mount Hood, a variety of glaciers flank the mountain, extend-
ing from near the crest at about 3400 m (about 11,200 ft) down
to an elevation of about 1800 m (6000 ft). These glaciers ring
the mountain on all sides, as shown in Figure 17.11b.
Continental Glaciers
In addition to mountain glaciers, another form of glacier is
called a continental glacier. As the name implies, a
continen-
tal glacier
is a gargantuan ice mass that covers a large part of
(b)
(a)
Figure 17.11 Cascade alpine glaciers.
(a) Mount Hood is a composite volcano that reaches an elevation of over 3400 m (11,200 ft) and
thus is an excellent place for the development of alpine glaciers. (b) This topographic map illustrates the various glaciers that ring the flanks
of Mount Hood.
Cirque
A bowl-like depression that serves as a source area for
some alpine glaciers.
Continental glacier
An enormous body of flowing ice that
covers a significant part of a large landmass.
