What color is snow and ice? If confronted with this question, you are likely to say white or clear, right?
If you answered that way, you'd be right most of the time, however there are certain times when ice appears to be blue in color such as in glaciers, holes or tunnels in the snow, old sea ice, and other assorted situations. This blue color can be very confusing to a person as it is a clear contrast from the clear or white color we associate ice and snow with, however there is scientific reasoning for why that particular phenomenon occurs.
When light passes through ice and snow, which is comprised of a great amount of ice crystals, red light is absorbed and blue light is transmitted, however because snow grains and ice crystals are rather large in size, all wavelengths of visible light are equally scattered so no particular color is allowed to dominate and make its presence known to the human eye due to the process of scattering.
Rather, what causes ice and snow to appear blue is its thickness. If ice or snow is very thick, it is possible for a great deal of red light to be absorbed, enough so that only blue light is transmitted making the ice look blue to the human eye. If you dig a hole in clean, deep ice or snow, you can see this process firsthand and view a gradiation of color from shallow depths to the deepest depths as a little red light is lost the deeper you go. The ice or snow at the surface of the hole is likely to be yellowish-redish and progress to yellowish-green, from there, greenish-blue, and eventually completely and totally blue in color.
Ice coloring is very important in determining how long it has been frozen and its strength,something important in several industries and activities such as fishing, ice-road trucking, climbing, exploring, etc. Most ice is white during its first year of existence due to the presence of a large amount of bubbles which cause light to scatter and travel only a short distance and leave the same color as it came in.
During the summer, the ice surface melts and new overlying ice layers compress the remaining air bubbles. Now, any light that enters travels a longer distance within the ice before it emerges. This gives the red end of the spectrum space enough to be absorbed, and the light returned at the surface is blue. During the warmer Summer months, the ice surface melts and new outer layers of ice form and alleviate many of the remaining air bubbles in the ice. Because of this, light is able to travel further into the ice and absorb the red light and return to the surface with blue light. Those who are experts in dealing with ice or have to because of their career choice know that older, bluer ice with only a few bubbles is stronger and a great deal safer than fresh white ice.
While not all ice and snow will appear blue in color, it can happen and it all has to do with how much and white kind of light is absorbed and transmitted.