Laboratory Manual for Introductory Geology 4e

FIGURE 15.2 Mountain and continental glaciers.
(a) The Crowfoot Glacier, a mountain glacier in Banff National Park, Canada.
(b) Continental glacier, Antarctica.
ice thousands of feet thick, dwarfing hills and burying all but the tallest peaks
(FIG. 15.2b). The North American and European continental glaciers did the same
during the Pleistocene.
15.2.2 How Glaciers Create Landforms
Glaciers erode destructional landforms and deposit constructional landforms. A
glacier can act as a bulldozer, scraping regolith (soil and unconsolidated sediment)
from an area and plowing it ahead. When it encounters bedrock, a glacier uses the
sediment it carries like grit in sandpaper to abrade the rock and carve unique landforms.
Glacial erosion occurs wherever ice is flowing, whether the glacier front is
advancing or retreating.
Depositional glacial landforms are equally distinctive: some are ridges tens or
hundreds of miles long; others are broad blankets of sediment. All form when
the ice in which the sediment is carried melts, generally when the glacier front is
retreating. Some sediment, called till, is deposited directly by the melting ice, but
some is carried away by meltwater; this sediment is called outwash [or glaciofluviatile
(glacial 1 stream) sediment]. Till and outwash particles differ in size, sorting, and
shape (FIG. 15.3) because of the different properties of the ice and meltwater that
deposited them.
Exercise 15.1 compares the ways in which glaciers and water do their geologic work.
15.3 Landscapes Produced by Continental
Glaciation
Both continental and mountain glaciers produce unique landforms not found in
areas affected by stream deposition and erosion. Landscapes formed by continental
glaciers differ from those formed by streams in every imaginable way, including the
shapes of hills, valleys, and stream divides, as well as the degree to which post-glacial
streams are integrated into stream networks like those discussed in Chapter 13.
FIGURE 15.4 illustrates the different shapes of valleys carved by continental glaciers
and by streams, and Exercise 15.2 explores their differences more fully.
15.3 LANDSCAPES PRODUCED BY CONTINENTAL GLACIATION
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