Why the Weird Spikes on Ice Cubes??

It’s about 6 am, I’m half asleep and getting a water bottle ready to bring to work. I open the freezer to get some ice cubes and see this:

Perhaps this is a common phenomenon, but in the 40+ years I’ve been on Earth, I somehow managed never to see it. What could cause these ice tentacles to climb out of my ice cube tray? I wondered.

Mini black hole, or some other gravitational anomaly forming in my freezer overnight? Aliens? Prankster Gremlins?

Ok, probably not.

I googled it. Alas, the answer is a little more mundane, but still interesting.

As most of us recall from elementary school science class, water expands as it turns to ice. This explains why my ice cubes try to burst from the tray when I over fill it, but how does this explain the little stalagmites on my ice cubes?

Note: Stalagmites grow from the ground up. Stalactites grow from the ceiling down (I know someone out there was wondering).

If something (like a little pocket of water, for example) is immersed in a cold environment (like a freezer) it will get colder from the outside in. Which means, our water becomes ice and expands from the outside in. This will cause pressure to increase on the still-liquid center of the ice cube. Sometimes, this pressure will be sufficient to break a hole through the layer of ice forming on the outside of the cube before the inner water freezes too.

Then, a little bit of the water squeezes out through the hole. This little bit of water is now on the colder outside and starts to freeze, but at the same time it is also being pushed up from below by more water trying to escape the squeeze.

Mind you, this is all happening very slowly. The result is that the water has time to freeze as it rises bit by bit. And voila! By the time the entire ice cube is frozen it has an ice spike sticking out of its top.

There you go. Your moment of science for today.

I’m not sure if I should wonder why this doesn’t happen on all ice cubes, or whether I should marvel that conditions are ever just right for the water to freeze just as it rises above the surface of the ice cube but before it falls and spreads out.