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Blue snow

My wife and I have spent the better part of the day digging out from the snowstorm, doing the driveway in stages. I noticed something I never had before; some of the shoveled snow has a faint blue cast to it. I don’t think I was imagining it, since my wife saw it too.

I remember when I was in Alaska learning that glaciers get a distinctly blue cast because the ice is extremely low in oxygen, which, at least if this site is correct, is not the cause of blue snow, which apparently has something to do with the scattering of light, in a process that is apparently the reverse of what makes the sky blue:

When light passes through ice, however, the red light is absorbed while the blue is transmitted. Were the operating process scattering as in the atmosphere, then the transmitted light would be red, not blue. However, because of the large size of snow grains and ice crystals, all wavelengths of visible light are scattered equally. Scattering therefore does not play an appreciable role in determining the color of the transmitted light. It takes an appreciable thickness of pure ice to absorb enough red light so that only the blue is transmitted. You can see the effect in snow at fairly shallow depths because the light is bounced around repeatedly between ice grains, losing a little red at each bounce. You can even see a gradation of color within a hole poked in clean, deep snow. Near the opening, the transmitted light will be yellowish. As the depth increases, the corer will pass through yellowish-green, greenish-blue and finally vivid blue. If the hole is deep enough, the color and light disappear completely when all the light is absorbed.

I have no idea if this accounts for the phenomenon that we observed. Maybe it was another sign that God hates gays, like dying birds in Arkansas.

Update: I think I actually managed to capture the blue cast in this picture, which you might have to make full screen (double click on pic) to see.

Have I just been missing this for the past 60 years?

One Comment

  1. MAB wrote:

    And I thought it was because the shovels were dark blue and dark green. And they shown through the snow…Interesting, because the snow was the same color in Norwich.

    Thursday, January 13, 2011 at 8:44 am | Permalink

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