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Needle ice, also known as Pipkrake, is commonly found hoisting pebbles and small clumps of dirt above moist fine-grained soils on crisp winter mornings. In actual fact, the needles themselves sit atop thin water films that supply ice growth from below - hence the need for moist ground conditions to provide an available water source. This is in stark contrast to the case for hoar frost, which is of a similar scale, but forms from water supplied through the air and is easily recognized by the appearance of side branches and a generally more dendritic structure. Instead, needle ice is closely related to the phenomena of frost heave, in which layers of ice called lenses form in horizontal sequences that push the soil grains out of the way and cause the ground surface to heave. Frost heave causes enormous damage to roadways and other man-made structures and is also one of the most important weathering mechanisms at high altitudes and in polar regions - possibly even a controlling mechanism in determining the shapes of the mountains themselves through its role in breaking rocks and creating scree. The physical weathering produced by needle ice is of a much smaller scale, but nevertheless provides an important mechanism for liberating nutrients useful to alpine vegetation.
Alan Rempel
Department of Geological Sciences
University of Oregon
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