South-looking, May 1995, photograph showing a number
of rounded blocks of glacier ice that are partly
buried in sediment deposited by a 1994 Jokulhaup
that occurred at the terminus of Bering Glacier,
Chugach National Forest, Chugach Mountains, Alaska.
The ice boulders were partially exhumed by later
discharge that eroded their entombing sediment.
The largest ice boulder is ~ 60 feet in maximum
dimension. Note the helicopter for scale. Bering
Glacier flows through Wrangell-Saint Elias National
Park. |
Pit Pond
A depression in an outwash plain by the melting of a block
of ice floated to its depositional site by meltwater and subsequently
buried by sediment. As it melts, a depression in the surface
of the outwash plain develops.
|
South-looking, May 1995, oblique aerial photograph
showing the rounded blocks of glacier ice shown
immediately above and a number of additional blocks
that are still partly buried in sediment deposited
by a 1994 Jokulhaup that occurred at the terminus
of Bering Glacier, Chugach National Forest, Chugach
Mountains, Alaska. In the area south of the middle
of the photograph, no ice boulders have been exhumed.
The largest ice boulder is ~ 60 feet in maximum
dimension. Bering Glacier flows through Wrangell-Saint
Elias National Park. |
|
South-looking, August 1995, oblique aerial photograph
showing a close-up of the lower right-hand area
shown on the photograph immediately above. All of
the rounded blocks of glacier ice shown above have
melted away, causing a reversal of topography and
the development of numerous pit ponds. Many individual
pit ponds have coalesced to form larger, complex
basins. Bering Glacier, Chugach National Forest,
Chugach Mountains, Alaska. The largest complex basin
is > 200 feet long. Bering Glacier flows through
Wrangell-Saint Elias National Park. |
|
|
Pleistocene
The epoch of geologic time, informally called the 'The
Great Ice Age' or the 'Glacial Epoch', that began ~1.8
million years ago and ended ~8,000 years ago (see the
CVO's Geologic
Time Scale). During this interval continental glaciers
repeatedly formed and covered significant parts of the
Earth's surface. Together, the Holocene and Pleistocene
epochs comprise the Quaternary Period.
|
|
Plucking
The mechanical removal of pieces of rock from a bedrock
face that is in contact with glacier ice. Blocks are quarried
and
prepared for removal by the freezing and thawing of water
in cracks, joints, and fractures. The resulting pieces are
frozen into the glacier ice and transported.
West-looking photograph of a plucked and frost-shatter
unnamed nunatak, projecting through the surface
of the Taku Glacier, Juneau Icefield, Coast Mountains,
Tongass National Forest, Alaska. Note the people
on the ridge for scale. |
|
|
|
U.S. Department of the Interior |
U.S. Geological Survey