The pool in my back yard froze over, and now that it's warmer it is starting to break up. But I notice that the ice is marred by fractures, and that they all seem to be completely vertical. Handling the ice indeed causes it to fragment into "sticks", for lack of better term.

This link points to an album of two short video clips to demonstrate.

Why does it do that?

Fractured ice

  • $\begingroup$ Nice observational skill. It might be the memory of the seeds around which the ice started forming. $\endgroup$
    – Alchimista
    Commented Mar 4, 2021 at 11:54
  • $\begingroup$ @alchimista thanks! This structure is pretty uniform across the entire surface of the water, not localised to one part, so I'm afraid I don't buy the "seed" argument. $\endgroup$
    – noughtnaut
    Commented Mar 4, 2021 at 12:06
  • $\begingroup$ Well the ice certainly starts by a sort of slurry, isn't? Kind of "onion stuff" finally meeting to form the pool plate. I think is something between boundaries rather than along a crystal plane... $\endgroup$
    – Alchimista
    Commented Mar 4, 2021 at 12:09
  • $\begingroup$ @Alchimista, I have reconsidered and now do buy the "seed" argument. However, that's not (yet) the full answer to my question. $\endgroup$
    – noughtnaut
    Commented Mar 10, 2021 at 20:33
  • $\begingroup$ that was indeed a suggestion $\endgroup$
    – Alchimista
    Commented Mar 10, 2021 at 22:56

2 Answers 2


Those are some pretty unusual chunks of ice - as you can see, the boundaries of the 'columns' are visible before he breaks them up. So what you've got is a crystalline solid which clearly is the merging of many "source" crystal starting points, or "seeds" as mentioned in the comments.

I can say with certainty from my many years of shinny on frozen ponds that ice does not typically form that way, or at least not at that small scale. I'm going out on a limb (but not on thin ice :-) ) and suggesting that there was a lot of pollen or other small-size debris on your pool which acted as the seed locations for this ice.

  • $\begingroup$ Fair enough, let's go with the "pollen seed" argument. It's certainly plausible. But why, then, are the fracture lines so perfectly parallel that pieces slide neatly up and down against one-another? $\endgroup$
    – noughtnaut
    Commented Mar 10, 2021 at 20:32

I have seen this many times on lakes in Wisconsin. I would like to note that in my experience the lake water does not freeze like this. Instead it freezes solid with near isotropic properties in comparison. This occurs instead when the ice begins to melt. The "seed" argument, elaborated upon in Carl Witthoft's comment, is a good hypothesis for what causes the patterns seen. I would like to hypothesize that while sentiment may cause the starting points the vertically linear separations are due to melted water pooling and melting ice in channels straight down with gravity.


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