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Glossary of Glacier Terminology

Sérac

A jagged pinnacle or tower of glacier ice located on the surface of a glacier, formed as a glacier flows down an icefall or by the intersection of crevasses. Frequently, large areas of a glacier will be covered by séracs.


The terminus of McBride Glacier, Glacier Bay National Park, Alaska, showing numerous pyramidal topped séracs. The individual spires are more than 100 ft. high.

Snowbridge

A mass of snow that has accumulated in the top of an open crevasse, masking the existence of the crevasse. Frequently, a large void exists below the snowbridge.


Several foot-thick accumulation of snow covers the top of an open creavasse on the surface of the Malaspina Glacier, Wrangell-St.Elias National Park, Alaska.

Vegetation covers the ice which is no longer moving in the medial morain band of Bering Glacier. Chugach National Forest, Alaska.

Stagnation

The in-situ melting of glacier ice. Many glaciers have stagnant termini, covered by thick sediment debris. Some support vegetation, including mature forests.


Water-filled melt-pits dot the surface of bering glacier's stagnant medial moraine. Chugach National Forest, Alaska.

Fairweather Glacier's mature spruce and hemlock trees are growing on the surface of the stagnant melting terminus, Glacier Bay, Alaska.

Mature spruce trees are falling into the Pacific Ocean at the stagnant termnus of Malaspina Glacier at Satkigi Bluffs, Wrangell-St.Elias, Alaska.

Striations

Multiple, generally parallel, linear grooves, carved by rocks frozen in the bed of a glacier into the bedrock over which it flows.


Recently-emerged striations, located in bedrock adjacent to the terminus of Guyot Glacier in Icy Bay, Wrangell-St.Elias, Alaska. Note the penny for scale.

Suncups

A series of bowl-like depression melted into a snow or ice surface, separated by a network of connected ridges. Individual suncups may be more than three feet deep and ten feet in diameter. Suncups form during warm, sunny conditions.


Differential melting has produced a field of up to two foot-high sun cups on the surface of the Malaspina Glacier, Wrangell-St.Elias, Alaska.

Surge

A short-lived, frequently large-scale, increase in the rate of movement of the ice within a glacier. Ice velocities may increase 10 to 100 times above normal flow rates. In some surges, the terminus of a glacier rapidly advances. Although not all glaciers surge, those that do often surge with some sort of a periodicity.


The fractured and rapidly-calving terminus of the surging Bering Glacier, Oct. 1993, Chugach Mountains, in Alaska.

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