Every upcicle is against one wall of a hollow metal post about a meter tall. I see water in there, but maybe 15–20 cm down. (Maybe that's ice too?)

The ice inside the post generally has a lenticular cross section with one arc flat against the metal, although one had a triangular shape.

They protrude up to 8–10 cm, often with one or more stair-steps away from the center, sometimes with an extremely fragile, narrow neck. The upper parts may be round (unlike the part in the post) or flat.

So are these kin to the ice spikes seen in ice cube trays? They're so big! And they're not freestanding, but are instead all stuck to the inner face of the posts.

How would they grow? It looks like they were pushed up out of the post and then maybe went through some freeze/thaw cycles that created those stairsteps, and the ridges on that 4th pic in the first post.

I really wish I could set up a camera to capture some growing.

Maybe I could set out a hollow post to grow my own?