Scientific Colloquium
April 30, 2004

Sorted circles, meter scale patterns consisting of circular soil domains surrounded by raised annular stone domains, are found in Arctic and high alpine environments in which the uppermost layer of soil (the active layer) experiences cyclic freezing and thawing.  These patterns exhibit a striking circular plan form, a convex upward soil domain surface on which motion is outward from the center, and tilt in the subsurface consistent with circulation. Sorted circles are just one of the many incredible sorted patterns found in these environments, including: polygons, labyrinths, islands and stripes.  Additionally, sorted patterns are a small subset of the diverse range of patterns found in cold climates, including: earth hummocks, palsas, pingos, ice wedge networks, etc.  Less obstructed by the biological agents that dominate temperate climates, cold environments team with self-organized patterns.  Frost heave, soil expansion by water migration during freezing, is the prime mover in the active layer, but what organizes that motion?  Sorted patterns can be understood in terms of self-organization owing to a few simple feedbacks between the transport processes that modify and the morphology that continually directs the evolution of the pattern.