The periglacial environment
149
horizontal lenticular layers of clear ice with variable thicknesses. They may form in situ
by ice segregation during the freezing process. Ice veins and wedges are vertical or
inclined cracks in the ground filled with ice. The wedges result from the growth of veins
by the supply of meteoric water. They are V-shaped, tapering downwards, with the ice
crystals having a vertical arrangement (Lachenbruch, 1962) (Figure 7.3) and
their expansive growth deforms the adjacent sediment. Ice wedges are commonly
2 to 3 m wide and penetrate about 5 to 8 m when resulting from epigenetic freezing. In
Siberia, syngenetic ice wedges formed in alluvium reach 5 m wide and 40 to 50 m deep
(Harry, 1988). They commonly form part of polygonal systems and if there is an
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Figure 7.3. Evolution of an ice wedge (Lachenbruch, 1962).