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More About Glaciers

Glaciers are often explained as being great rivers of ice that flow and shape the landscape, sculpting mountains and carving out valleys.

• Glaciers store about 75% of the world's freshwater.
• Glacierized areas cover more than 15,000,000 square kilometers of the Earth.
• Glacier ice crystals can grow to be as large as baseballs.
• Glacial ice often appears blue because ice absorbs all other colors except blue; which is reflected.
• Ice shelves may calve icebergs that are over 80 kilometers long.
• Almost 90% of an iceberg is below water - only about 10% shows above water.
• North America's longest glacier is the Bering Glacier in Alaska, measuring 204 kilometers long.

In regions of high winter snowfall and cool summer temperatures, snow can accumulate to a point where buried layers get compressed by the overlying snow. The pressure creates a thickened mass of ice.

When the mass of compressed ice reaches a critical thickness of about 18 meters, it begins to deform and move. Its sheer girth, in combination with the forces of gravity, causes a glacier to slowly move, or flow.

Glacier ice flows down mountain valleys, fans across plains, and spreads into the sea. As a glacier moves over the ground surface, friction causes the underside of the glacier to move more slowly while overlying glacier ice moves unimpeded.

Glacier retreat, melt, and ablation, result from increasing temperature, evaporation, and wind scouring. Ablation is a natural and seasonal part of glacier life. As long as snow accumulation equals or is greater than melt and ablation, glacier health is maintained.

Over the past 60 to 100 years, glaciers worldwide have tended toward retreat. Alpine glaciers, which are typically smaller and less stable to begin with, seem particularly susceptible to glacial retreat. Whether this is due to a predictable climate trend or because of increased human impacts on global climate remains to be determined.