Geology Reference
In-Depth Information
(A)
(B)
Figure 7.15.
Ice wedge rejuvenation. (A) Schematic diagram showing a buried (i.e. inactive) wedge
and modern wedges of single-, two-, and multi-stage nature. (B) Rejuvenated ice wedge, southern
Banks Island, Canada.
areas, they may attain widths of 1.0-2.0 m near the surface but are usually much smaller.
Epigenetic wedges rarely exceed 3.0-4.0 m in depth.
7.5.2. Syngenetic Wedges
Syngenetic ice wedges form at approximately the same time as the enclosing sediments
are laid down. In other words, as the ground surface rises, so the wedge grows upwards
in response to surface aggradation (Figure 7.14B). The typical locations for syngenetic
wedges are on fl oodplains, beneath peat, as in tundra polygons, and beneath gelifl uction
deposits, as at the bottom of a slope. The size and shape of a syngenetic wedge is a func-
tion of both horizontal and vertical growth rates. If sedimentation is high and ice-vein
accretion is low, then the wedge becomes thinner; if ice-accretion rate is high and sediment
accumulation is low, then the wedge becomes wider.
Syngenetic ice wedges appear to reach their greatest thickness and vertical dimensions
on ancient alluvial surfaces and river terraces in central Siberia (Dostovalov and Popov,
