(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.