While hiking up to Summit Peak in the Porcupine Mountains this past weekend (not quite as impressive as it sounds; as I said at the time, “peak” is a relative term and we were in Michigan), we came across a patch of mud at the edge of the trail with some unusual ice crystals sprouting out of it.
The shape actually reminded us of string cheese, only smaller – delicate curlicues of ice growing out of the surface of the soil. I’d never seen anything like it before, but we found several more patches of them as we walked, all growing out of exposed mud.
It turns out this phenomenon is called “needle ice.” It only occurs when the air temperature is below freezing but the soil temperature isn’t – in other words, in the fall before the soil freezes for the winter. Liquid water in the soil is drawn up to the surface through capillary action and is extruded in columns through pores in the soil as it freezes. This is more or less what we’d guessed was happening.
And if you’re wondering, here’s what the view from Summit Peak, the highest point in Michigan’s Upper Peninsula, looked like this first weekend in November. That’s Lake Superior on the horizon, although it blends so seamlessly with the sky that it’s hard to tell. (Click to enlarge.)