How snowflakes get their shapes

Not all snowflakes are unique in their shape. There's one fact for you.

And here's another: The shape of snowflakes — whether individually distinct or mass-production common — is determined by chemistry. Specifically, the shape is a function of the temperatures and meteorological conditions the snowflakes are exposed to as they form and the way those factors affect the growth of ice crystals.

This short video from Bytesize Science will give you a nice overview of snowflake production and will help you understand why some snowflakes are unique, and why others aren't.


  1. Neat video!  One thing I’ve wondered about snowflakes, and which the video doesn’t precisely answer, is why the six arms of a snowflake are identical to one another.  Although the video explains how the six sides of the prism that forms around the dust particle acquire depressions due to heat differentials, I don’t understand why these depressions should be the “same”, let alone why they should lead to identical arm-shapes as they grow more and more complicated.  Why don’t snowflakes have six totally distinct arm-shapes?


      1. Thanks so much!  That video completely answered my question.  Better yet, the answer is pretty damn neat.  Basically the arms are uniform because their growth is a direct expression of the atmospheric conditions they’re passing through (temperature, moisture, etc).  Since they all pass through the same conditions together, they grow in the same way.  Snowflake as dynamic sculptural thermometer/hygrometer — fabulous.

    2. They’re promoting a common misconception:  the wrong idea that snowflakes flutter around, or that they fall edge-on.

      Actually, snowflakes orient face down like little dinner plates.

      When I found out about this, I understood everything, EVERYTHING!!!!


      At the scale of a snowflake (they’re under 1mm across,) the air acts very viscous.   Any fluttering gets damped out.  (Think of dust settling in a sunbeam.  Micro people could walk around on any flat-falling snowflakes.)   And because they’re face-on to the vertical wind, there’s a dead zone in front as well as behind the disk-like shape.  Only the edges of the ice are seeing lots of new, vapor-laden air, so only the edges are growing fast.    (Hmmm, wouldn’t this setup *cause* the flat shape?  If they tumbled, they’d end up as little prisms or even spheres,  no?)

      And at the small scale of a snowflake, the temperature & humidity is the same all around the edge, and all parts change simultaneously.  The flake may penetrate through turbulent plumes of temp/humd variation, so all the growing dendrites change form at once.

      At Museum of Science, Boston, we had a huge MIT snowflake-growing machine with flat tanks of supercooled water and crossed polarizers.   That thing could grow individual flakes a few cm across!   Underwater flakes, yet the same flat-with-dendritic-edges form.

      For weirdness, go search:  Electric Snow Crystal

  2. Browsing over the title, I first read it as ‘how cornflakes get their shape’.  Which left me immensely indifferent.  But snowflakes … that’s another matter.  

    Random forms produced by machines and people vs. geometrical forms produced by nature. Offering an elegant and clear view on the laws of physics

  3. From my observations the arms of a particular snowflake are not identical, just fairly similar. Often even the branch patterns are a bit different between arms and the size of side branches varies a bit. My understanding is that there is no central organizing principle in the center the guides the branching each arm grows independently. The arms size and branches are formed as some function of temperature and saturation of the air with water and probably some other things, and the arms experience very much the same conditions they grow in a similar way. A different flake that falls next to another may have experienced a very different cycling of temperature etc. so it has a different pattern of growth.

  4. What, no celestial jibber about makerbots condensing on particular winter nights? Does everyone else have an app to save that stuff up for particular days’ articles as if it were an auction?

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