earth

What is Needle Ice?

[When] the air temperature at ground level is below 32° F, but the soil temperature is just above 32°, the conditions are set. This most often happens on clear mountain nights when the air temperatures drop precipitously after a warm sunny day. Water in the moist soil is drawn to the surface by capillary action, where it rises to meet the cold air, freezing rapidly. The ice initially forms in small pores and crevices where it continues to collect ice, creating columns that push the ground up.

This ice forms as a growing column of crystalline filaments instead of a solid block of ice because of the constant motion of the groundwater. The needle ice pushes small soil particles skyward, raising the ground level slightly in a superficial crust. It will look like you're stepping onto solid ground, and it is a bit jarring when your foot falls down a couple of inches deeper than expected.

The sound of the ice needles collapsing sounds like the tinkling of glass chandelier crystals. If you've ever walked over crunchy ground on a cold morning, you've probably tread on needle ice.