Patterned Grounds

The repeated annual freezing and thawing of permafrost soils can produce very interesting geometric features called patterned ground. These include polygons, circles, nets, steps, and stripes. They typically occur in periglacial regions such as those in Siberia, Canada, Alaska, Iceland, Greenland, Antarctica and the Andes. The actual process by which these patterns form had long puzzled scientists but the introduction of computer-generated geological models in the past 20 years has allowed scientists to relate the formation of these features to phenomena associated with frost heaving, which refers to expansion that occurs when wet, fine-grained, and porous soils freeze.

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From Wikipedia:

The repeated freezing and thawing of groundwater forces larger stones toward the surface as smaller soils flow and settle underneath larger stones. Areas that are rich in larger stones contain much less water than highly porous areas of finer grained sediments. These water saturated areas of finer sediments have a much greater ability to expand and contract as freezing and thawing occur, leading to lateral forces which ultimately pile larger stones into clusters and stripes. Through time, repeated freeze-thaw cycles smooth out irregularities and odd-shaped piles to form the common polygons, circular, and stripes of patterned ground.

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Patterned ground in Katmai National Park, Alaska. Photo credit: epod.usra.edu

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Photo credit: www.geol.umd.edu

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Patterned Ground on Ile de la Possession in the Crozet Islands. Photo credit: yannig/Wikimedia

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Partially melted and collapsed lithalsas (heaved mounds found in permafrost) have left circle-like structures on the Svalbard Archipelago. Photo credit: Hannes Grobe/Wikimedia

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Patterned ground as illustrated by sorted circles (rifle for comparison of size), in Svalbard, Norway Photo credit: USGS

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Photo credit: permafrost.gi.alaska.edu

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Patterned ground can occur on any planet that has ice below its surface. This picture was taken on Mars indicating the presence of water on the Red Planet. Photo credit: NASA/JPL/University of Arizona

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