I. How do glaciers form?
- A. Glacial material
is composed of thick masses of ice derived from snowfall.
- 1. When a thick
accumulation of snow builds up, compression takes place.
- a. Air bubbles
are driven out of the snow.
- b. Fluffy snowflakes
change to granular ice (called firn), and then to solid glacial ice.
- c. An inch
of rain corresponds to a foot of snow.
- 2. Melting during
the day and freezing at night aids in turning the ice into snow.
- B. Ice builds up so
much that it begins to flow, creating a glacier.
- 1. Glaciers tend
to build or accumulate at higher elevations. This is called the zone of accumulation.
- 2. Glaciers tend
to slide down to lower elevations where they melt. This is the zone of wastage
(sometimes called the zone of ablation).
- 3. A glacier begins
to form and advance when snow and ice accumulated from one winter survives
to the next winter.
- 4. A glacier retreats
when more snow/ice of the glacier melts during the summer than is accumulated
during the winter.
II. What are the major types
of glacier?
- A. Alpine glaciers
(also called mountain glaciers) form in mountainous regions and tend to be
confined to valleys between mountain ridges.
- 1. Alpine glaciers
have characteristics of rivers and solid rock.
- a. Like
rivers, alpine glaciers flow fastest at the top an center; they are slowest
around the sides and bottom.
- b. Like
rocks, ice behaves brittly near the surface of the ice sheet; ice behaves
ductilely deeper in the ice sheet (below ~40 meters), just as rocks do at
depth.
- 2. Erosional features
of Alpine glaciers
- a. U-shaped
valleys (example: Yosemite Valley)
- b. Hanging
valleys (example: Bridal Veil Falls, Yosemite National Park)
- c. Cirque
- d. Aretes
- e. Horn (example:
Matterhorn in the Swiss Alps)
- 3. Depositional
features of Alpine glaciers
- a. Moraines
- i. lateral
- ii. medial
- iii. end
moraines
- a.
terminal
- b.
recesional
- c.
ground
- B. Continental glaciers
(also refered to as ice sheets, ice caps, and sometimes ice fields) tend
to cover larger areas than alpine glaciers, and often persist at lower elevations.
Last update 5/17/2006
Webpage designed by Hiram Jackson.
Contact Geology webmanager, Hiram Jackson, at jacksoh@crc.losrios.edu
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