I finally made it to Mitakesan today, and while I would normally review the hike as a day trip from Tokyo, that will have to wait for another post since …. I found needle ice today!
I came down from the ridge on my hike today through a very shady forested section and noticed that my footsteps seemed crunchier than the scattered dry leaves could account for, and I stopped to investigate. When I looked, I found little ribbons of ice sticking out of the ground. Several were broke off, but most of them were still poking out of the ground and about 2 inches tall. They looked like extruded ribbons with several individual filaments at the base merging into one flat section, but oddly they all seemed to be about half an inch or so wide and then there would be another ribbon. Some were vertical and had bits of dirt and leaves on top of them, others were at angles and in some cases were nearly circular. When I turned around and looked at the trail from the other direction, there were patches of it all over.
Wikipedia has a good description of what causes needle ice:
Needle ice is a phenomenon that occurs when the temperature of the soil is above 0 °C (32 °F) and the surface temperature of the air is below 0 °C (32 °F). The subterranean liquid water is brought to the surface via capillary action, where it freezes and contributes to a growing needle-like ice column.