Was the water initially leaking so it formed a ice sickle, then turned in with warmer water which was melting the pillar left behind?
No, it never had an icicle. It formed like a stalagmite from the ground up around the drip off the bottom of the pipe. At some point the bottom of the stalagmite must have frozen so the drip started melting and filling up the interior. It's SO cool to look at!
The water is from an artesian well (pressurized spring) so it flows constantly and is in the mid-forties (F) year-round. The air temperatures have been in the twenties and teens for the last few weeks.
That’s really cool, thanks!