Blue Glow

This past week I went to Ice Castles in Woodstock with my brother and nephews. The "castle" was made out of millions of icicles. There was a distinct blue glow coming from them and it wasn't because of the colored lights built into them. 

It made me wonder what was going on. This is what I found out:

The heavy layers of ice press the air out of the deeper layers of ice. This not only removes much of the air, it also causes the ice to form large, dense crystals. When light hits these crystals, they absorb long red wavelengths of light. At the same time, they scatter short-waved blue light, which makes the ice appear blue. The longer the path light travels in ice, the more blue it appears.

Glaciers that have many cracks and crevices have many different kinds of blue reflecting. Take a look in this video.