Needle ice forms when the temperature of wet earth is above freezing, but the air is dry and below freezing.
The liquid water in the soil wicks to the surface via capillary action through small pores and cracks, where it freezes on contact with the cold air; it expands and forms a small ice cap atop the pore or crack. As more liquid water arrives from below, it also freezes and expands, pushing the previously-formed ice upward.
If the process goes on overnight, it can grow needle-like ice columns or mini-stalagmites that make for very crunchy walking!
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Close but no cigar! The way to remember cave formations is “Ants in your pants.” The mites go up and the tights go down. Mini-stalagmites.
Zig
I could blame autocorrect, but it was probably just a brain misfire on my part. 🙂 Thanks, I’ll correct it.
The skyline sure has changed since I worked there in the ’60s, but my building is still clearly visible in your crisp shot. I recall this kind of ice in my grade school playground – haven’t seen it since.