Blue ice (glacial)
Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of a glacier that winds its way toward a body of water (river, lake, ocean, etc.). During its travels, air bubbles that are trapped in the ice are squeezed out, and the size of the ice crystals increases, making it clear. A good example of blue ice was observed in Tasman Glacier, New Zealand in January 2011.
In some areas, earthquakes have raised the blue ice above the ground and created formations much like large frozen waves.
The blue color is often wrongly attributed to Rayleigh scattering. Rather, ice is blue for the same reason water is blue: it is a result of an overtone of an oxygen-hydrogen (O-H) bond stretch in water which absorbs light at the red end of the visible spectrum.
Antarctic runways 
Blue ice is exposed in areas of the Antarctic where there is no net addition or subtraction of snow. That is, any snow that falls in that area is counteracted by sublimation or other losses. These areas have been used as runways due to their hard ice surface which is suitable for aircraft fitted with wheels rather than skis.
See also 
- Why is ice blue?
- Glaciology of Blue Ice Areas in Antarctica
- Blue Ice in Antarctica
- Blue Ice Runways in Antarctica
- Blue Ice images from Antarctica