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Glossary of Glacier Terminology


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.

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