174
Climatic Geomorphology
Figure 8.4. Sorted polygons. Southern Shetland Islands, Antarctica. Scale 1 m. Photo: J. Ldpez Martfnez.
The nets are intermediate forms whose mesh is neither dominantly circular nor
polygonal and can be sorted or nonsorted. The hummocks are included in this type
(Figure 8.6). These are mounds of earth covered with vegetation that may reach 2 m in
diameter and 50 cm in height. Their internal structure displays cryoturbations. They occur
above the tree line (timber line) and their genesis seems to be related to mass
displacements (Schunke and Zoltai, 1988).
The steps are a type of patterned ground that corresponds to benches that develop in
slopes with a gradient between 3 and 20 ~ The margins of the nonsorted steps are covered
with vegetation (tuff-banked terraces) whereas in the sorted ones the borders are made up
of imbricated clasts (stone-banked terraces) (Sharp, 1942a). Very likely the nonsorted
steps derive from hummocks and the sorted steps from sorted circles and polygons
(Washburn, 1979). Their origin is considered to be related mainly to differential mass
displacement.
The stripes are strips oriented parallel to the steepest slope gradient. The nonsorted
stripes consist of parallel lines of vegetation-covered ground and intervening strips of
relatively bare ground. The sorted stripes are parallel lines of stones and intervening strips
of fine material with the later tending to be several times wider than the coarser lines
Climatic Geomorphology
Figure 8.4. Sorted polygons. Southern Shetland Islands, Antarctica. Scale 1 m. Photo: J. Ldpez Martfnez.
The nets are intermediate forms whose mesh is neither dominantly circular nor
polygonal and can be sorted or nonsorted. The hummocks are included in this type
(Figure 8.6). These are mounds of earth covered with vegetation that may reach 2 m in
diameter and 50 cm in height. Their internal structure displays cryoturbations. They occur
above the tree line (timber line) and their genesis seems to be related to mass
displacements (Schunke and Zoltai, 1988).
The steps are a type of patterned ground that corresponds to benches that develop in
slopes with a gradient between 3 and 20 ~ The margins of the nonsorted steps are covered
with vegetation (tuff-banked terraces) whereas in the sorted ones the borders are made up
of imbricated clasts (stone-banked terraces) (Sharp, 1942a). Very likely the nonsorted
steps derive from hummocks and the sorted steps from sorted circles and polygons
(Washburn, 1979). Their origin is considered to be related mainly to differential mass
displacement.
The stripes are strips oriented parallel to the steepest slope gradient. The nonsorted
stripes consist of parallel lines of vegetation-covered ground and intervening strips of
relatively bare ground. The sorted stripes are parallel lines of stones and intervening strips
of fine material with the later tending to be several times wider than the coarser lines