Page 365 - Laboratory Manual in Physical Geology

MOUNTAIN CONTINENTAL
EROSIONAL FEATURES OF GLACIATED REGIONS
GLACIATION GLACIATION
Bowl-shaped depression on a high mountain slope, formed by a
Cirque X
cirque glacier

Sharp, jagged, knife-edge ridge between two cirques or glaciated
Arête X
valleys

Col Mountain pass formed by the headward erosion of cirques X

Steep-sided, pyramid-shaped peak produced by headward erosion
Horn X
of several cirques
Steep slope or rock cliff at the upslope end of a glaciated valley or
Headwall X
cirque

U-shaped, steep-walled, glaciated valley formed by the scouring
Glacial trough X
action of a valley glacier

Hanging valley Glacial trough of a tributary glacier, elevated above the main trough X

Asymmetrical knoll or small hill of bedrock, formed by glacial
abrasion on the smooth stoss side (side from which the glacier
Roche moutonnée X
came) and by plucking (prying and pulling by glacial ice) on the
less-smooth lee side (down-glacier side)
Glacial striations Parallel linear scratches and grooves in bedrock surfaces, resulting X X
and grooves from glacial scouring

Smooth bedrock surfaces caused by glacial abrasion (sanding
Glacial polish X X
action of glaciers analogous to sanding of wood with sandpaper)

FIGURE 13.5 Erosional features of mountain or continental glaciation.

Nisqually Glacier—A Global ACTIVITY
Thermometer? 13.6 The Changing Extent of

Nisqually Glacier is one of many active valley glaciers that Sea Ice
occupy the radial drainage of Mt. Rainier—an active volcano
|
located near Seattle, Washington, in the Cascade Range of
THINK How is the cryosphere affected by
the western United States. Nisqually Glacier occurs on the
About It climate change?
southern side of Mt. Rainier and flows south toward the
Nisqually River Bridge in FIGURE 13.15 . The position of the
OBJECTIVE Measure how the extent of sea ice has
glacier’s terminus (downhill end) was first recorded in 1840,
changed annually in the past, predict how it may
and it has been measured and mapped by numerous geologists

change in the future, and infer what benefits or hazards

since that time. The map in FIGURE 13.15 was prepared by

could result if Arctic sea ice continues to decline.
the U.S. Geological Survey in 1976 and shows where the
terminus of Nisqually Glacier was located at various times PROCEDURES
from 1840 to 1997. (The 1994, 1997, and 2010 positions
1. Before you begin, read Sea Ice. Also, this is what
were added for this laboratory, based on NHAP aerial
you will need:
photographs and satellite imagery.) Notice how the glacier has
____ 30 cm (12 in.) length of thread or thin string
more or less retreated up the valley since 1840.
____ ruler, calculator
Sea Ice ____ Activity 13.7 Worksheets (pp. 355–356) and
pencil
Sea ice is frozen ocean water. The largest masses of sea
2. Then follow your instructor’s directions for
ice occur in the Arctic Ocean and around the continent
completing the worksheets.

of Antarctica ( FIGURE 13.16 ). In both locations, the sea

Glaciers and the Dynamic Cryosphere ■ 335