The periglacial environment
169
3.6. Eolian action
In the Arctic and Antarctic regions the extreme cold and arid conditions impede the growth
of vegetation so that the wind may be an important activity. During the Pleistocene, the
transport and sedimentation of eolian particles had a great importance in Europe (Kasse,
1997) and in the centre of the United States (Embleton and King, 1975a,b). While the cover
sands constitute continuous deposits in central Europe, in Great Britain they are patchy.
Between the Last Glacial Maximum and the beginning of the Holocene, three phases of
eolian sand deposition have been identified. These phases do not coincide strictly with
stadial or glacial conditions. Aridity, scarce vegetation cover and delayed responses of the
eolian activity to climatic change determine the timing of eolian phases (Kasse, 2002).
Besides, the wind plays a relevant role in the redistribution of the snow during the winter.
In summer it melts more rapidly on the sun-facing slopes. These changes in the snow cover
are very important for nivation processes and the generation of landforms such as
asymmetric valleys and oriented lakes that will be assessed below. In these cold polar
regions, the wind action operates predominantly in summer, causing the deflation of fine
particles from the land surface generating periglacial pavements on alluvial plains and till
accumulations. Overdeepening due to differential eolian erosion may give rise to deflation
basins (Sepp~il~i, 2004). The abrasion caused by the blasting of wind-transported particles
on the ground produces ventifacts or faceted clasts, yardangs in rock outcrops (elongated
mushroom shapes), microyardangs in loose sediments (small-scale knife-shaped and
aligned landforms), and tafonis close to the base of rock slopes (French, 1996).
Figure 7.23. Summer atmospheric pressures (isobars) and wind directions in Europe during the Late
Glacial period. H and L: High and low pressures (modified from Poser, 1950).
169
3.6. Eolian action
In the Arctic and Antarctic regions the extreme cold and arid conditions impede the growth
of vegetation so that the wind may be an important activity. During the Pleistocene, the
transport and sedimentation of eolian particles had a great importance in Europe (Kasse,
1997) and in the centre of the United States (Embleton and King, 1975a,b). While the cover
sands constitute continuous deposits in central Europe, in Great Britain they are patchy.
Between the Last Glacial Maximum and the beginning of the Holocene, three phases of
eolian sand deposition have been identified. These phases do not coincide strictly with
stadial or glacial conditions. Aridity, scarce vegetation cover and delayed responses of the
eolian activity to climatic change determine the timing of eolian phases (Kasse, 2002).
Besides, the wind plays a relevant role in the redistribution of the snow during the winter.
In summer it melts more rapidly on the sun-facing slopes. These changes in the snow cover
are very important for nivation processes and the generation of landforms such as
asymmetric valleys and oriented lakes that will be assessed below. In these cold polar
regions, the wind action operates predominantly in summer, causing the deflation of fine
particles from the land surface generating periglacial pavements on alluvial plains and till
accumulations. Overdeepening due to differential eolian erosion may give rise to deflation
basins (Sepp~il~i, 2004). The abrasion caused by the blasting of wind-transported particles
on the ground produces ventifacts or faceted clasts, yardangs in rock outcrops (elongated
mushroom shapes), microyardangs in loose sediments (small-scale knife-shaped and
aligned landforms), and tafonis close to the base of rock slopes (French, 1996).
Figure 7.23. Summer atmospheric pressures (isobars) and wind directions in Europe during the Late
Glacial period. H and L: High and low pressures (modified from Poser, 1950).