glacier flour

a fine powder of silt- and clay-sized particles that a glacier creates as its rock-laden ice scrapes over bedrock; usually flushed out in meltwater streams and causes water to look powdery gray; lakes and oceans that fill with glacier flour may develop a banded appearance; also called rock flour.

glacier flood

a sudden outburst of water released by a glacier.

glacier fire

a phenomenon in which strong reflection of the sun on an icy surface causes a glacier to look like it is on fire.

glacier cave

a cave of ice, usually underneath a glacier and formed by meltwater; cave entrances are often enlarged near a glacier terminus by warm winds; most common on stagnant portions of glaciers.
A small stream flows from the glacier cave at the terminus of Arolla Glacier in the Pennine Alps. Photograph from 1902. (Photo courtesy of H.F. Reid, archived at the World Data Center for Glaciology, Boulder, CO.)


a mass of ice that originates on land, usually having an area larger than one tenth of a square kilometer; many believe that a glacier must show some type of movement; others believe that a glacier can show evidence of past or present movement.
Taku Glacier winds through the mountains of southeastern Alaska, calving small icebergs into Taku Inlet. This photograph dates from 1929. (Photo courtesy of the U. S. Navy, archived at the World Data Center for Glaciology, Boulder, CO.)


land covered in the past by any form of glacier is said to be glaciated.

glacial trough

a large u-shaped valley formed from a v-shaped valley by glacial erosion.
Western Brook glacial trough, Newfoundland, Canada. The sheer walls of this glacial trough soar up to 700 m high, and the glacial basin is 500 m deep in places. (Photo courtesy of Natural Resources Canada. Copyright Terrain Sciences Division, Geological Survey of Canada.)

glacial till

accumulations of unsorted, unstratified mixtures of clay, silt, sand, gravel, and boulders; the usual composition of a moraine.

glacial striations

grooves or gouges cut into the bedrock by gravel and rocks carried by glacial ice and meltwater; also called glacial grooves.
Striated Graywackie, Yale Glacier, Alaska. 1997. Parallel striations and bedrock fracture trends (across the left side of the image) are clearly visible in this photo. (Photo courtesy of Tom Lowell, University of Cincinnati.)

glacial retreat

when the position of a mountain glacier's terminus is farther upvalley than before; occurs when a glacier ablates more material at its terminus than it transports into that region.
Muir Glacier, Glacier Bay National Park and Reserve's White Thunder Ridge as seen on August 13, 1941 (left) and August 31, 2004 (right). (2004 photo courtesy of B. Molnia, USGS; 1941 photo courtesy of W. Field. Archived in the Long-Term Change Photograph Pairs Special Collection in the Glacier...


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