Delicate threads push up from the soil at this time of year. What are they?
Needle Ice! The water, soil type, and temperatures all have to be just right for these frosty pillars to form:
-The soil needs to be somewhat porous (tightly packed enough to retain water and loose enough so there is space for the water to move up through the soil – usually this is silty soil).
-The soil must be saturated, so all the pores are full of water.
-The soil temperature must be above freezing and the air temperature must be below freezing (this is usually in the late fall/early winter as soil takes longer to cool than air).
-The ground is usually bare, such as a hiking trail.
Under this perfect combination of conditions, water at or just below the soil surface reaches the colder air and freezes. Capillary action brings up more water from the soil, which then freezes and expands, freezes and expands, pushing up from the soil in fragile tubes. The dirt is lifted up as the needle ice grows!
Thinner columns of ice (about as thick as our hair and aptly named hair ice) grow from wood with Exidiopsis effusa fungus on humid nights when the temperature is just below freezing. See a timelapse here.