Photo: Franz Joseph Glacier, New Zealand

Taken May 25, 2007

Pop quiz hot shots: if you ever find yourself on a glacier hike in New Zealand (and you should, it’s great fun!) what makes the ice blue instead of the white we’re used to?

Answer: it depends on the light that’s reflected.  Atoms interact with wavelengths of light differently causing some to be reflected and some to be absorbed, so for example something is black when it absorbs all the light hitting it (and why black objects get hot!).  Everyone’s favorite life-sustaining molecule, H2O, vibrates in a way that absorbs light towards the red side of the spectrum, leaving the blue color you see above.

So why is ice and snow usually white then?  For the simple reason that virtually all the light you see hitting a snowy surface is scattered a few times and eventually reflects back, giving white, and this overwhelms the faint blue color water normally has.  It’s only when the light is absorbed by the water (you usually need around a meter of it) that the blue makes it through, similar to how coffee looks light when poured but much darker in a cup.

And that is why glaciers look so damn cool.  The more you know…

7 responses to “Photo: Franz Joseph Glacier, New Zealand

  1. Fantastic post! I used to study glaciers in Alaska and had the hardest time making people understand when I got back that most of my experience was pale blue and gray, not white. =)

    • astrowright, thanks! Alaska sounds awesome and yeah lots of gray ice on the bottom of the glacier, but that’s not half as interesting to explain as the pretty blues. 🙂

  2. The photos looks remarkably like it was photo-shopped… maybe I will try to make a version of it with me, to see how hard it is to do!

    • Steven, thanks I think? This was my Facebook picture for a long while so I’m going to use that as evidence that it’s actually real. *wink*

    • Looks shopped because the lighting is completely diffuse in there and there is no flat ground.

      /Random comment by random stranger

      • Hi!

        I assure you this image is very real indeed- light is diffuse because it’s ice all around, and no flat ground because glaciers don’t melt evenly. Lots of other pictures like mine can be found on a Google search. 🙂


      • That’s what I meant. In retrospect I should’ve added “despite being clearly real”.

        /Random stranger

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