Why did my ice freeze in a pointy way

Question

I froze an ice cube and there was a thing that looked like an upside down icicle in the middle. Can someone explain this?

Answer 1

Hi Lauren!

I don't know exactly what kind of shape you saw but I think I have an idea!

The YouTube channel Veritasium has a great video explaining this phenomena titled "Ice Spikes Explained".

The quick summary is that as the liquid water in the tray starts to solidify into ice, it does so from the outside-inward. Ice has a fairly unusual property in that Ice is less dense than its liquid form -- or, put another way, ice expands as it freezes. As such, the forming "ice shell" exerts an increasing inward pressure on the liquid water in its center.

The liquid water doesn't have many options for how to escape this crushing pressure from the surrounding ice, so it can pop a tiny hole into the top surface of the ice and start to leak out to relieve the pressure. Leaked water quickly freezes into ice, forming a sort of hollow ice tube, which then acts as a tube for the leakage of more of the internal water, which then refreezes -- this slowly grows an "upward icicle". The icicle/tube eventually stops growing whenever the "tube opening" freezes over.

This is a really cool phenomena which is entirely dependent upon water's tendency to *expand* when freezing -- so almost any other liquid should *not* exhibit this phenomena!

The video will explain it a lot clearer that I can in words, so I'd give it a watch if you are interested!

Best,

--Zach