Patterned ground

Patterned ground is the distinct, and often symmetrical natural pattern of geometric shapes formed by ground material in periglacial regions. Typically found in remote regions of the Arctic, Antarctica, and the Australian outback, but also found anywhere that freezing and thawing of soil alternate; patterned ground has also been observed on Mars. The geometric shapes and patterns associated with patterned ground are often mistaken as artistic human creations. The mechanism of the formation of patterned ground had long puzzled scientists, but the introduction of computer-generated geological models in the past 20 years has allowed scientists to relate it to frost heaving, the expansion that occurs when wet, fine-grained, and porous soils freeze.

Patterned ground can be found in a variety of forms. Typically, the type of patterned ground in a given area is related to the prevalence of larger stones in local soils and the frequency of freeze-thaw cycles.

Polygons can form either in permafrost areas (as ice wedges) or in areas that are affected by seasonal frost. The rocks that make up these raised stone rings typically decrease in size with depth.

In the northern reaches of the Canadian Boreal forests, when bogs reach a eutrophic climax and create a sedge mat, Tamarack Larch and Black Spruce are often the early colonists within such a polygonal climax sedge mat.

Circles range in size from a few centimeters to several meters in diameter. Circles can consist of both sorted and unsorted material, and generally occur with fine sediments in the center surrounded by a circle of larger stones. Unsorted circles are similar, but rather than being surrounded by a circle of larger stones, they are bounded by a circular margin of vegetation.

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