When Noah and I visited Cole (Cold) Mountain, we stumbled (physically) upon this phenomenon all along our walk home. Since discovering it, we’ve since noticed it along many paths across our Virginia winter trips (McAfee’s Knob, Sharp Top, and Sulpher Spring Trail). Upon further research, I now understand it. It’s Needle Ice.
This interesting occurrence forms when the temperature of the soil is above zero degrees Celsius (0 °C, 32 °F) and the temperature of the surrounding air is below zero degrees Celsius (0 °C, 32 °F). In a process called Ice Segregation, cold water moves through a medium toward the presence of ice, freezes at the interface and adds to the ice. When this occurs at or near the surface of soil it produces Needle Ice, which takes the form of strands of ice rising vertical from the surface or near surface of the soil.
Needle ice requires a flowing form of water underneath the surface, from that point it comes into contact with air that is below freezing. This area of the process usually occurs at night when temperature peaks its low point. From then on, it produces a needle like structure as we know as “Needle Ice”.
The ice needles are typically a few centimeters long. While growing, they may lift or push away small soil particles. On sloped surfaces, needle ice may be a factor contributing to soil creep. Alternate names for needle ice are “frost pillars” and “frost columns,” and similar happenstances can occur on living or dead plants, and on wood.
You see different things when you go out in different seasons!