Glacial ice is composed of ice crystals, snow, air, water and sediments. Glaciers are mainly formed from compressed snow, with only a small proportion due to freezing of water. Glaciers form when more snow accumulates over the year than melts during the summer. As layers of snow accumulate, the buried snow grains become more and more tightly packed and are converted to firn which subsequently metamorphoses to glacial ice as the firn recrystallizes.

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