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Glossary of Glacier Terminology

Debris Cone

A cone or mound of debris-covered ice, with a thick enough sediment cover to protect the ice from melting.


Southeast-looking photograph showing four conical debris cones sitting on the ablating surface of the Bucher Glacier, adjacent to its confluence with the Gilkey Glacier, Juneau Icefield, Tongass National Forest, Coast Mountains, Alaska. The tallest of the cones is ~ 4 m high. The debris cones' sediment accumulated in a crevasse.

Dendrochronology


Photograph of the exposed roots and lower trunk of a tree that has recently eroded out of its entraining glacial sediment, Muir Inlet, Glacier Bay National Park, Alaska. The top of the tree was sheared off by an advance of Muir Glacier ~ 8,000 years ago.

The study of tree rings and subfossil wood to provide information about the glacial and climatic history of an area.


Photograph of several exposed tree trunks, recently eroded out of glacial-lacustrine sediment, south of the eastern margin of Bering Glacier, Alaska. The slab of wood that was cut from the tree in the foreground will have its rings analyzed and will have samples of individual rings radiocarbon dated. The tree was sheared off by an advance of Being Glacier ~ 1,500 years ago. Photograph by Austin Post. Bering Glacier flows through Wrangell-Saint Elias National Park.

September 10, 2001 LANDSAT 7 TM image showing a large disarticulation event occurring at Bering Glacier, Coast Mountains, Alaska. The width of the disarticulation area is ~ 1.0 mile.

Disarticulation

Disarticulation is the process through which large blocks of ice, sometimes greater than .5 miles in width, detach from the thinning and retreating terminus of a glacier that ends in a body of water. Disarticulation occurs as the terminus thins to where its buoyandcy no longer permits it to remain in contact with its bed. As the glacier begins to float free and rises off the bottom it rapidly comes apart along old fracture scars and crevasses. For example, at Bering Glacier, in the Chugach Mountains, Alaska, a single observed disarticulation event resulted in nearly 2/3 of a mile of terminus retreat in a single day. As many as 100 discrete, tabular pieces of glacier ice have been observed separating from the glacier's terminus in a single event. Bering Glacier flows through Wrangell-St. Elias National Park, Alaska.


Northeast-looking oblique aerial photograph of a large disarticulation event occurring at Bering Glacier, Coast Mountains, Alaska in August 2001. The width of the disarticulation area is ~ 1.0 mile. This is the same location shown in the LANDSAT image below.

Distributary

A tongue of glacier ice that flows away from the main trunk of the glacier. This may result from differential melting changing the gradient of part of a glacier.


Southwest-looking photograph of the terminus of Worthington Glacier, showing several small distributaries diverging from the main trunk of the glacier, Chugach National Forest, Chugach Mountains, Alaska.

Downwasting

The thinning of a glacier due to the melting of ice. This loss of thickness may occur in both moving and stagnant ice. Also called Thinning.


Northeast-looking near-vertical aerial photograph of the east margin of Muir Glacier. Both debris-covered and bare pieces of ice are sitting on recently-exposed bedrock adjacent to the glacier margin. The ice at the right edge of the photograph was stranded by the rapid thinning of the glacier, Muir Inlet, St Elias mountains, Glacier Bay National Park, Alaska.

Drift

A collective term used to describe all types of glacier sedimentary deposits, regardless of the size or amount of sorting. The term includes all sediment that is transported by a glacier, whether it is deposited directly by a glacier or indirectly by running water that originates from a glacier.


North-looking near-vertical aerial photograph of a 1-mile by 1.5-mile area recently-exposed by the retreat of Bering Glacier. The ground surface is covered by glacial sediment deposited in several ways, including as lodgement and ablation till, and as crevasse fill, Bering Glacier, Alaska. Bering Glacier flows through Wrangell-Saint Elias National Park.

Photograph of the flank of a drumlin composed of glacial till. The length of this drumlin is ~ 1/8 mile. Note the two people for scale. Cranes Beach, MA.

Drumlin

An elongated ridge of glacial sediment sculpted by ice moving over the bed of a glacier. Generally, the down-glacier end is oval or rounded and the up-glacier end tapers. The shape is often compared to an inverted, blunt-ended canoe. Although not common in Alaska, drumlins cover parts of the Eastern and Midwestern United States (Irish).


North-oblique aerial photograph of the fluted and drumlin-covered landsurface, north of Milwaukee, WI. The field of view is ~ 7 by 18 miles.

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