Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 247

tion of the soil (fine-grained is best), and (4) the orientation of the freezing plane. A
nonsorted circle displays no difference in particle size; its form is usually determined
by the bordering vegetation. Similarly, sorted polygons contain rocks along the pattern
lines with finer material between them, while nonsorted polygons are the result of a
cracking matrix at the surface with no difference in the size of material. In Finnish La-
pland, remote sensing data helped classify nonsorted patterned ground, which is more
common at lower elevations where the ground moisture and vegetation are abundant,
and sorted patterned ground, which occurs at high elevations with steeper slopes and
sparse vegetation (Hjort and Luoto 2006). Sorted stripes (stone stripes) are marked by
alternating zones of larger and finer particles, while nonsorted stripes may be identified
by ridges and furrows or by alternating bare and vegetated strips. Although both types
of patterned ground present recognizable and conspicuous patterns, the sorted vari-
ety is the most intriguing, both because it has a more striking appearance and because
the segregation of rock sizes suggests a more complex origin. Moreover, the sorting is
both vertical and horizontal. The larger particles that compose the borders character-
istically accumulate in a wedge shape. The cross section of the wedge has the widest
part near the soil surface and tapers downward. In addition, the largest rocks are near
the surface, progressively getting smaller with depth. In small-scale features, the stony
margins are typically composed of pea-sized particles extending to a depth of only a
few centimeters, while in large-scale features, the rocks may be sizable, extending to a
depth of 1 m or more.