Chapter 8
Periglacial landforms
The previously described cold-climate processes give rise to a wide variety of periglacial
landforms. There are two main environments where these features are especially abundant.
The high-latitude areas with markedly seasonal contrasts and the middle- and low-latitude
alpine zones like the Andes, Himalaya, or the mountains of equatorial Africa characterised
by strong daily fluctuations. The differences in the climatic conditions have an important
influence in most of the processes responsible for the generation of periglacial landforms
(King, 1976a,b).
The variations in the climatic belts during the Pleistocene have caused changes in the
distribution of the periglacial environments. It is important to differentiate between relict
and active periglacial landforms. The identification of relict landforms allows us to infer
the existence of past periglacial conditions in certain areas (Washburn, 1979).
1. Patterned ground
Patterned ground corresponds to a group of small-scale landforms with circular, polygonal,
and stripped geometries that raised the attention of the first explorers of the periglacial
regions to the detriment of other more widespread landforms (French, 1996). Patterned
ground is not specific to periglacial areas alone, however, and similar morphologies are
developed in other environments, especially in the hot desert (Hunt and Washburn, 1966).
Therefore, a situation of equifinality or morphological convergence takes place because
different processes under distinct conditions give place to similar landforms. It is very
important to bear in mind this circumstance when trying to deduce past environmental
conditions from relict landforms and depositional features. In the subdesertic central sector
of the Ebro Depression around Zaragoza city (NE Spain), several researchers (Johnson,
1960; Brosche, 1971, 1972) interpreted structures found in fluvial terrace deposits
overlying Tertiary evaporites as ice wedges and cryoturbations. Recent studies, however,
have demonstrated that they were generated by subsidence-related process caused by
the karstification of the soluble bedrock (Zuidam, 1976a,b). Only those morphologies
generated by the thermal cracking of frozen ground are specific of periglacial environments because they indicate the presence of permafrost or intense cold conditions.
Periglacial patterned ground generates in the active layer and is classified, according
to the classical morphologic systematisation of Washburn (1956) into circles, polygons,
nets, steps, and stripes. The presence or absence of particle sorting is considered for each
of the types. The circles, polygons, and nets develop mainly on horizontal surfaces. These
cells tend to lengthen with slopes between 2 and 7 ~ becoming stripes (Sharpe, 1938; Bfidel,
1960) (Figure 8.1).
Periglacial landforms
The previously described cold-climate processes give rise to a wide variety of periglacial
landforms. There are two main environments where these features are especially abundant.
The high-latitude areas with markedly seasonal contrasts and the middle- and low-latitude
alpine zones like the Andes, Himalaya, or the mountains of equatorial Africa characterised
by strong daily fluctuations. The differences in the climatic conditions have an important
influence in most of the processes responsible for the generation of periglacial landforms
(King, 1976a,b).
The variations in the climatic belts during the Pleistocene have caused changes in the
distribution of the periglacial environments. It is important to differentiate between relict
and active periglacial landforms. The identification of relict landforms allows us to infer
the existence of past periglacial conditions in certain areas (Washburn, 1979).
1. Patterned ground
Patterned ground corresponds to a group of small-scale landforms with circular, polygonal,
and stripped geometries that raised the attention of the first explorers of the periglacial
regions to the detriment of other more widespread landforms (French, 1996). Patterned
ground is not specific to periglacial areas alone, however, and similar morphologies are
developed in other environments, especially in the hot desert (Hunt and Washburn, 1966).
Therefore, a situation of equifinality or morphological convergence takes place because
different processes under distinct conditions give place to similar landforms. It is very
important to bear in mind this circumstance when trying to deduce past environmental
conditions from relict landforms and depositional features. In the subdesertic central sector
of the Ebro Depression around Zaragoza city (NE Spain), several researchers (Johnson,
1960; Brosche, 1971, 1972) interpreted structures found in fluvial terrace deposits
overlying Tertiary evaporites as ice wedges and cryoturbations. Recent studies, however,
have demonstrated that they were generated by subsidence-related process caused by
the karstification of the soluble bedrock (Zuidam, 1976a,b). Only those morphologies
generated by the thermal cracking of frozen ground are specific of periglacial environments because they indicate the presence of permafrost or intense cold conditions.
Periglacial patterned ground generates in the active layer and is classified, according
to the classical morphologic systematisation of Washburn (1956) into circles, polygons,
nets, steps, and stripes. The presence or absence of particle sorting is considered for each
of the types. The circles, polygons, and nets develop mainly on horizontal surfaces. These
cells tend to lengthen with slopes between 2 and 7 ~ becoming stripes (Sharpe, 1938; Bfidel,
1960) (Figure 8.1).