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.

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 centimetres 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" ("Säuleneis" in German), "frost column", "Kammeis" (a German term meaning "comb ice"), "Stängeleis" (another German term referring to the stem-like structures), "shimobashira" (霜柱, a Japanese term meaning frost pillars), or "pipkrake" (from Swedish pipa (tube) and krake (weak, fine), coined in 1907 by Henrik Hesselman).

The similar phenomena of frost flowers and hair ice can occur on living or dead plants, especially on wood.

In order for needle ice to form there needs to be a process of Ice Segregation, which only occurs in a porous medium when supercooled water freezes into existing ice, growing away from the ice/water interface. As water permeates the ice, it becomes segregated into separate pieces of ice in the form of lenses, ribbons, needles, layers or strands of ice.

Needle ice is commonly found along stream banks or soil terraces. It is also found by gaps around stones and others areas of patterned ground. The variety of soil properties also affects where its found. Places where the soil is much deeper and richer can affect the growth of the ice. Consequently, the deeper the soil, the larger the water content allows it to develop. It can be evidently formed anywhere where underground water is exposed to open (freezing) air.

...
Wikipedia