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Definition:
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(1) Ice that is part of a glacier, as opposed to other forms of frozen water such as ground ice and sea ice. (2) Ice that is part of a glacier, having formed by the compaction and recrystallization of snow to a point at which few of the remaining voids are connected, and having survived at least one ablation season. In this more restricted sense, the term refers to the body of the glacier, excluding not only snow and firn but also superimposed ice, accreted ice and marine ice. See zone. The density at which voids cease to form a connected network, that is, the density at which firn becomes glacier ice, is conventionally taken to be near to 830 kg m-3. Ice in, or originating from, a glacier, whether on land or floating on the sea as icebergs, bergy bits, or growlers. Snowflakes are compressed under the weight of the overlying snowpack. Individual crystal near the melting point have slick liquid edges allowing them to glide along other crystal planes and to readjust the space between them. Where the crystals touch they bond together, squeezing the air between them to the surface or into bubbles. During summer we might see the crystal metamorphosis occur more rapidly because of water percolation between the crystals. By summer's end the result is firn -- a compacted snow with the appearance of wet sugar, but with a hardness that makes it resistant to all but the most dedicated snow shovelers! Several years are usually required for the snow to settle and to season into the substance we call glacier ice. Above the firnline, snow that falls each year packs down and changes into glacier ice as air is slowly forced out of it. Ice in, or originating from, a glacier, whether on land or floating on the sea as icebergs, bergy bits or growlers.
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