I went up to Indian River Falls today and noticed a number of small streams that were still flowing with little ice (while others, sometimes larger streams, were frozen solid). I think the free flowing water must have come out of the ground at a temperature well above freezing and a flow rate such that, despite the cold temperatures, the stream stayed relatively ice free for a while. On one such stream I noticed what were probably the largest needle ice formations I have ever seen. They were at least 6-9 inches tall and seemed to have grown out of the silt/clay that made up part of the stream bed. It was interesting to see the clear layering. I am guessing they represent a cycle of night/day or warmer/cooler, but I am not sure.
I’m not sure how these ice formations are created, but a little internet research indicated that it involves hydrostatic pressure from ground water pushing up the ice. It’s unclear to me why/how that action would be working in this case, since the surface water is right next to the ice formations.