Glacial ice structure

  1. I'm not familiar with earth science, in particular ice formation in glaciers and I hope you can bear my rather stupid question:
    Is the change of a "normal" ice layer into glacial ice with frozen air bubbles a continous transition or a spontaneous reaction?
    Someone told me that the air bubbles inside the snow flake in an ice layer start to freeze. How can air, this mixture of nitrogen, oxygen, carbon dioxide, ... actually freeze? It was a professor of meteorology, who told me that on a winterschool and I tend to believe him but I fail in understanding him.
    Are there any other changes in the ice solid structure (due to the high pressure), besides that effect of frozen air? Something like a phase transition into a solid-crystal structure? I mean the ice appears to be blue and that might be an indicator of a different absorption effect or a change into a crystal structure.
     
  2. jcsd
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  3. Tanja,

    The air bubbles are not frozen. They are merely trapped by the ice surrounding them. Glacial ice for this reason is less dense than ice formed by freezing liquid water.

    The blue tint is from the absorption of red light by the water molecule as a result of it's quantum vibrational modes. The same reason that lakes, oceans, and rivers appear blue.
     
  4. Must be a misunderstanding. The ice and snow at the ice sheets remain frozen allmost all the time. However as snow accumulates yearly the lower layers start to compress under the pressure and form crude icy snow or "firn" with air moving freely around. As the pressure increases at about 80-90 meters depth the ice grains become solid ice, trapping the air in bubbles.

    See also: http://www.crrel.usace.army.mil/sid/Summit/background.htm
    http://www.carleton.edu/departments/GEOL/Links/AlumContributions/blueice/firn.html
     
  5. Hello Skyhunter,

    thanks for your answer.
    But there's one question left
    Why does water in oceans, lakes and the glacial ice change its bleuish color if you look at it from different angles? If the color's origin are water quantum vibrational modes rather than light scattering it shouldn't depend on the angle. I might be wrong.

    And does this vibritional frequency change as soon as ice turns into glacial ice?
     
  6. Looking at it from different angles is changing the angle of the reflected light you are observing. Since there is only a slight absorption in the visible bandwidth the blue hue is easily negated or intensified by the angle of light.
     
  7. Up, that was a fast answer.
    Ok, you nearly convinced me. Another last question: Why is water in my water glas not blue. And I had a look at a deep water tank that didn't appear to be blue at all.
    And if it's a slight blue absoprtion, why are some small lakes and small pieces of glaciers very blue? You can see, that I still stick a bit to the pure reflection theory :-).
     
  8. Not to my knowledge. It is derived from the shape of the water molecule and it's magnetic dipole. To change the frequencies that the molecule responds to would necessitate changing the shape of the molecule. Although pure H2O does not exist in nature, so the composition of the ice could determine it's hue.

    Each atom has it's own magnetic field. When atoms organize into molecules their magnetic fields overlap and interact. The strength of the bonds determine how a molecule vibrates.

    Here is a great cite to learn about water.
     
  9. From my previous source.
    We were both partially correct. It is a combination of both.
     
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