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Concept
Pipkrake
Résumé
Needle ice is a needle-shaped column of ice formed by groundwater. Needle ice forms when the temperature of the soil is above and the surface temperature of the air is below . Liquid water underground rises to the surface by capillary action, and then freezes and contributes to a growing needle-like ice column. The process usually occurs at night when the air temperature reaches its minimum.
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", "Spew Ice", "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 it is 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.
Needle ice is most suitable in soils with a high silt and organic matter content. Needle ice consists of groups of narrow ice slivers that are up to several centimeters long.
Source officielle
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