Glaciers

Glaciers are created in areas where the air temperature never gets warm enough to completely melt snow. Snowflakes may partially melt when they come into contact with the ground; as the air temperature drops further, the partially melted snow refreezes, turning into ice. The resulting mixture of snow and ice is compacted as additional layers of snow accumulate on top. Eighty percent of fresh snow is air; as the weight of fresh upper layers of snow and ice increases, air is pressed out of the lower layers, producing ice that contains less than 20–air. As the years pass, snow accumulates and the slab of ice grows steadily thicker (if the glacier is in a growth phase). Eventually, the layer of ice becomes so massive that it begins to flow slowly downhill. When an ice mass begins to flow under the influence of gravity, it is considered a glacier.