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Glossary of Glacier Terminology

For definitions of Ice Cap, Ice Field and Icesheet see Glacier Types

South-looking photograph showing an outcrop of the Miocene age Yakataga Formation, Gulf of Alaska shoreline, Glacier Bay National Park, Alaska. The unit consists of ice-transported sand to boulder-size coarse-grained sediment in a glacial silt matrix.

Ice Rafting

The transportation of glacier sediment away from the ice margin by icebergs. Sediment transported by floating ice and deposited in the ocean is called glacial-marine sediment. Deposited in lakes, it is called glacial-lacustrine sediment.

North-looking photograph showing two icebergs that are transporting significant quantities of glacially-eroded sediment, Johns Hopkins Inlet, Glacier Bay National Park, Alaska. As these icebergs melt and roll-over, the entrained sediment will be released into the water column.

USGS map of Antarctica showing the location of ice shelves in darker blue from Fact Sheet 050-98.

Ice Shelf

The floating terminus of a glacier, typically formed when a terrestrial glacier flow into a deep water basin, such as in Antarctica and the Canadian Arctic.

LANDSAT MSS image of a large iceberg separating from the Larsen Ice Shelf. The berg is more than 50 miles long.

North-looking photograph showing an iceberg shaped like a dragon, towering ~ 15 feet above the waters of Muir Inlet, Glacier Bay National Park, Alaska.


A block of ice that has broken or calved from the face of a glacier and is floating in a body of marine of fresh water. Alaskan icebergs rarely exceed 500 feet in maximum dimension. In order of increasing size, the following names are used: Brash Ice, Growler, Bergy Bit.

North-looking photograph showing an iceberg shaped like a mushroom, towering ~ 15 feet above the waters of Muir Inlet, Glacier Bay National Park, Alaska.

North-looking photograph showing 300+-foot-long iceberg towering more than 40 feet above the waters of Portage Lake, Chugach National Forest, Chugach Mountains, Alaska.

Near vertical aerial photograph of the southwest coast of Greenland (upper right) flanked by a large, dense field of drifting icebergs. Most icebergs are less than 400 feet in maximum length, but the large berg in the upper left is at least 1/4-mile in length.

Ice-Dammed Lake

A lake that exists because its water is restricted from flowing by an ice dam. Sometimes these lakes form because an advancing glacier had blocked a valley.

Northeast-looking oblique aerial photograph showing the floor of a recently drained, ice-dammed lake, a part of Berg Lake, Chugach National Forest, Chugach Mountains, Alaska. The numerous sub-circular depressions on the lake floor suggest that the floor of the lake is ice-cored. As this part of the glacier's terminus thinned and narrowed, the lake was able to drain around the perimeter of the lake. This lake is an ice-marginal lake.


Part of a glacier where the ice flows over a bed with a very steep gradient, typically at a higher rate than both above and below. As a result the surface is fractured and heavily crevassed. In a river system, this would be a waterfall.

Northwest-looking photograph of the Vaughn Lewis Icefall, a steep, > 1,500 foot bedrock cliff over which the Vaughn Lewis Glacier descends from the upper Juneau Icefield, Tongass National Forest, Alaska.

Ice-Marginal Lake

A lake that is located adjacent to the terminus of a glacier. Typically, these lakes form in bedrock basins scoured by the glacier. They enlarge as the glacier retreats. Sometimes they are dammed by an End or Recessional Moraine.

North-looking oblique aerial photograph showing Harlequin Lake, an ice-marginal, moraine-dammed lake, located adjacent tot the terminus of Yakutat Glacier, Tongass National Forest, Saint Elias Mountains, Alaska. The Dangerous River is the meandering stream that drains the Lake at the lower left.


The balance between changes within the Earth's crust and mantle, where material is displaced in response to an increase (isostatic depression) or decrease (isostatic rebound) in mass at any point on the Earth's surface above. Such changes are frequently caused by advances or retreats of glaciers.

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