Ice, which is water in its frozen, solid state, will form when the water temperature reaches 320 F. In cold weather, ice appears on rivers, lakes, and the ocean. In area where it is perpetually cold, ice becomes part of the landscape as features such as glaciers, ice caps, and ice sheets.

    Glaciers form in locations where snow accumulates faster than it can melt, usually in mountains areas. Over time the snow becomes compressed and recrystallizes into ice. When the ice reaches a solid mass of a certain thickness it can begin to move, or flow, under its own weight. Most glaciers move very slowly, perhaps only a few inches a year, but under circumstances, they can advance quickly.

    An ice cap is a thick layer of ice and snow that has formed a permanent crust over areas of land. Such formations are found primarily in polar regions. Sometimes the term ice cup is used interchangeably with ice sheet, although an ice sheet usually is larger. Ice sheet that cover continents are known as continental glaciers, such as Antarctic ice sheet.

Adopted from: National Geographic, Answer Book 10,001 Fast Fact about Our World, Washington DC, National Geographic, 2015.

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