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I recently saw this picture posted on Twitter which shows a so-called ice spike rising from an ice cube tray.

Ice Spike from Ice Cube Tray

I have read the Wikipedia page, but it doesn't mean much to me. My instinct was that it is caused by vibrations from the freezer setting up a resonant frequency on the surface of the water, and the spike has gradually "built up" as the water freezes. But I'm not a physicist, so I don't know if this makes sense. I'm ideally looking for a layman's explanation of why this happens.

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    $\begingroup$ Since ice spikes occur naturally in birdbaths, which do not have motors giving a steady source of vibration, I suspect that your instinct is incorrect. $\endgroup$
    – Peter Shor
    Jul 13, 2013 at 11:42
  • $\begingroup$ I think, it has more to do with the right temperature than the vibration. Look at a snow-flake. Ice freezes in patterns, straight lines and angles. It has to do with the shape water makes as it freezes and the outside of the spike freezing while the inside is still wet. If it freezes too slow, no spike. it it freezes too fast, the potential spike would freeze on top and the ice would buckle. It happens in bird baths too. Vibration isn't necessary. You can play with making ice spikes if you have an adjustable temperature dial on your freezer. Use distilled water for best results. $\endgroup$
    – userLTK
    Mar 25, 2015 at 12:54

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I think what is happening in rough qualitative terms is that the water freezes around the sides and the top first leaving a hole in the centre. Ice expands by 4%-9% when freezing so as the water below freezes it forces the remaining water up through the hole where is freezes around the edge. The hole shrinks as the water freezes and rises around its edge forming the base of the spike. The spike is hollow so water is pushed up to the top where it freezes at the edge making the spoke grow longer

Update: If you search for ice spike on youtube you will find some good timelapse videos showing these spikes forming. I especially like this one because you can see the unfrozen water pushing up inside the spike.

Sometimes in a larger water container you can get an inverted pyramid shape. The explanation is the same and the shape is due to the crystaline nature of the ice. This video shows the phenomena

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  • $\begingroup$ why wouldn't it push the already frozen ice upwards? $\endgroup$
    – udiboy1209
    Jul 13, 2013 at 14:16
  • $\begingroup$ in bird baths the hole could be around some impurity that changes the freezing properties. $\endgroup$
    – anna v
    Jul 13, 2013 at 14:58
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    $\begingroup$ @udiboy, the ice is attached rigidly to the sides so it wont be pushed up if there is an easier way to exit at the centre. Ice will often start at the edges because crystals nucleates on the rough surface, so it sticks there and grows outwards towards the centre $\endgroup$
    – Philip Gibbs - inactive
    Jul 13, 2013 at 15:44
  • $\begingroup$ @PhilipGibbs I thought the ice would firmly stick to the walls of the container due to normal forces resulting from sideways expansion, which happens AFTER a complete lump of ice has formed. Are the ice-container bonds strong enough to keep it in place without that happening? $\endgroup$
    – udiboy1209
    Jul 13, 2013 at 17:14
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    $\begingroup$ @udiboy If the ice froze over the whole surface it would probably move up as the ice expanded but if there is a hole to allow the water to push through then the forces trying to float the ice upwards are very small. The least bit of stickiness would hold it in place. If that was not never the case I suppose we would never see ice spikes. $\endgroup$
    – Philip Gibbs - inactive
    Jul 13, 2013 at 18:56

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