More snow in Chicago

It snowed till late evening here last night, though we don’t have the ten inches originally predicted. There is enough, though, to cause cancellation of flights at O’Hare and Midway. And enough for students at my University to make a cool snowman (snowperson?). The mohawk hairdo is made from coffee stirrers purloined from the dining hall. I love the leafy necklace:

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And here’s a mystery: footprints in ice. Can you explain this? Remember, it snowed twice in the past two days, with nearly a day’s break between.

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31 Comments

  1. Randall Schenck
    Posted December 12, 2016 at 8:15 am | Permalink

    I think the way that works is – after the first snow, people walk thru it. Melting occurs and then another freeze sets in. More snow is swept away leaving the frozen prints.

  2. Posted December 12, 2016 at 8:15 am | Permalink

    compressed snow takes longer to melt

  3. Kevin Meredith
    Posted December 12, 2016 at 8:18 am | Permalink

    When the snow fell, it was lightly packed. Stepping on it packed it tighter. When the air warms above 32C, lightly packed snow is more porous to that air and melts more quickly than tightly packed snow.

    • Draken
      Posted December 12, 2016 at 8:22 am | Permalink

      At 32C, there’s more melting than just snow 🙂

      I suppose you meant °F.

      • Kevin Meredith
        Posted December 12, 2016 at 9:27 am | Permalink

        Thanks, I did mean F

      • gravelinspector-Aidan
        Posted December 12, 2016 at 3:12 pm | Permalink

        Gallium.
        Brie.

  4. Draken
    Posted December 12, 2016 at 8:19 am | Permalink

    This leads to the question: is Mohawk hair on a snowman cultural appropriation? Now fortunately this is Uchicago, because if it were for example Brown, may the snowgods help you…

    • Posted December 12, 2016 at 10:11 am | Permalink

      “This leads to the question: is Mohawk hair on a snowman cultural appropriation?”

      I wondered that as well, but I think it’s OK if the snow is native to America.

      • gravelinspector-Aidan
        Posted December 12, 2016 at 3:13 pm | Permalink

        Surely all snow is immigrant snow from Antarctica.? Someone should build a wall.

  5. Posted December 12, 2016 at 8:23 am | Permalink

    I believe the ice footprints come from a multi-step process like this:

    1. Semi-wet snow is walked on and compressed (and if it’s possible to make a snowman, the snow is definitely wet enough for this).
    2. Temperature continues to drop below freezing, making the packed wet snow icy. If the temperature was below freezing the whole time, the ground could still be warm enough to cause this effect. Sometimes.
    3. Snow removal in the form of a forward-spinning brush on a small Bobcat-style vehicle removes all the lighter, unpacked snow. This includes the snow around the footprints that hasn’t been packed into dense ice and isn’t firmly attached to the concrete.

    I saw this a lot less out at Montana State in Bozeman, where the temperatures were below freezing long enough (and the snow dry enough) that the snow would simply pack into squeaky white footprints instead. No melting.

    • Posted December 12, 2016 at 11:01 am | Permalink

      Correct analysis, in my opinion. +1.

  6. Mark Sturtevant
    Posted December 12, 2016 at 8:39 am | Permalink

    I see a lot of naturalistic explanations about the footprints, but no one suggested the alternative supernaturalistic ones. People here are clearly biased in their views.

    Cool snowman, though. Its’ got personality.

    • Randall Schenck
      Posted December 12, 2016 at 8:52 am | Permalink

      Hell yes, it’s Sasquatch. Or his little brother.

      • gravelinspector-Aidan
        Posted December 12, 2016 at 3:21 pm | Permalink

        … wearing a plain-heeled shoe on one foot and a ridged-heel shoe on the other. Obviously a sasquatch of studied sartorial elegance.

    • Desnes Diev
      Posted December 12, 2016 at 11:13 am | Permalink

      Maybe Jack Frost decided to go for footprint (and “tireprint”) patterns on sidewalks. Fen patterns on windows can be boring.

      Something like that happened another time in another world (see Hogfather by T. Pratchett).

  7. JJH
    Posted December 12, 2016 at 8:39 am | Permalink

    It’s easy. It snowed and melted. Then, Frosty walked through and left his footprints behind.

    • Alpha Neil
      Posted December 12, 2016 at 9:55 am | Permalink

      Where there is only one set of tracks is when frosty was carrying me.

      • JJH
        Posted December 12, 2016 at 12:09 pm | Permalink

        Excellent!

      • Posted December 12, 2016 at 12:24 pm | Permalink

        lol

      • Diane G.
        Posted December 13, 2016 at 1:03 am | Permalink

        + lol

  8. rickflick
    Posted December 12, 2016 at 9:09 am | Permalink

    It’s clear to me that the snowman (looks male to me) with personality created the prints. He leaves a bit of himself wherever he goes.

  9. Kevin
    Posted December 12, 2016 at 9:51 am | Permalink

    My kids are not allowed to walk on the driveway until I shovel it. That’s da roolz. Otherwise I get exactly that kind of mess that never seems to come off until sun.

    • George
      Posted December 12, 2016 at 10:06 am | Permalink

      Worst is when you have to drive on the driveway before you clear the snow. I have those tire track impressions right now. Came home on Saturday night (northwest suburb of Chicago) with about 2″ of snow on the ground. Drove through it to get the car into the garage. Did not clear the snow until last night (about 8″ by then) and the tire tracks will be there for a while.

  10. Alpha Neil
    Posted December 12, 2016 at 9:54 am | Permalink

    The icy footprints reminded me of the beautiful ancient footprints photo posted recently.

  11. enl
    Posted December 12, 2016 at 11:05 am | Permalink

    Not snowman. Not snowperson. “individual of frozen water crystal descent”.

    • Posted December 12, 2016 at 12:53 pm | Permalink

      You’ll have to specify what form of crsytalization, otherwise you’re confusing snow with the other crystallization, ice. And that would be racist, or something.

      • harrync
        Posted December 12, 2016 at 2:40 pm | Permalink

        It has been scientifically proven that snow crystals are genetically superior to ice crystals. I know this is true because, following the precedent set by our President-elect, I just made it up.

        • Posted December 12, 2016 at 2:52 pm | Permalink

          If it weren’t for Trump getting elected and ending The War On Christmas™ this year, we’d all be watching Frosty, the Androgynous Crystalline Water Formation again. Now, it’s okay to say snowMAN! He is already Making America Great Again!

      • gravelinspector-Aidan
        Posted December 12, 2016 at 3:35 pm | Permalink

        I don’t think that you get any unusual crystalline structures of ice until something fairly above (Earth) surface pressures. [Checks phase diagram – diffuse transition to a cubic form around -100degC and a sharper transition to tetragonal (3 orthogonal symmetry axes, but differing cell dimensions) at around 2kbar pressure.
        Ice is a good substance for scaring people with their first phase diagram because it’s a (fairly) pure compound. Then you can get onto the complex things like mixtures and immiscible phases in some parts of P-T space, or having to draw your diagrams with a third composition axis.

  12. Posted December 12, 2016 at 2:24 pm | Permalink

    The footprints can only be a sign from God. He’s all powerful but prefers subtle hints that require a moment’s thought to figure out. The Footprints of the Lord. Amen.

  13. cherrybombsim
    Posted December 12, 2016 at 7:28 pm | Permalink

    I can see someone has used salt on the sidewalk with the footprints. The footprints are smushed down and less porous than the rest of the snow, where the salty water can seep through and melt more snow.


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