xkcd #3115: Unsolved Physics Problems
Title text:
'Tin pest' makes more sense to me. Tin just doesn't want to be locked down in a shape like that. I get it. But why would any metal want to grow hair??
Transcript:
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Source: https://xkcd.com/3115/
Similarly, ice spikes. You can make em at home, and we really don't understand how or why they form.
I think it's been figured out for a while now? Essentially most of the surface freezes, except for a small hole. The spike forms from that hole since the water is pushed out before freezing (on the outside) leaving a hollow spike.
The rate of freezing is similar to the rate of extrusion, a spike can form.
I thought there was a relatively good explanation for ice spikes having to do with the volumetric expansion of water as it transitions phases from liquid to solid. Basically as an ice cube freezes there is a shell formed over the top surface and under the right circumstances it forms from the outside edges in leaving a hole, but then instead of the hole closing over ice starts forming downward into the bulk of the cube, pushing liquid water out of the hole which is then frozen into a protrusion
https://en.m.wikipedia.org/wiki/Ice_spike