Geology Reference
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Figure 6.2. Sand wedges. (A) Oblique aerial view from 200 m of double-rimmed sand-wedge poly-
gons formed on glacial outwash sediments, Peary Land, North Greenland. (B) Wind-blown sand
infi lling a thermal-contraction crack, Taylor Dry Valley, Southern Victoria Land, Antarctica. Both
photos were supplied courtesy of the late Professor T. L. Péwé.
Fractures that develop primarily in the seasonally-frozen layer have been described
from Siberia (Danilova, 1956; Dylik, 1966; Katasonov, 1973; Katsonov and Ivanov, 1973).
They appear to be typical of cold continental climates and probably refl ect the thickness
of the zone of seasonal freezing and thawing. Apparently similar structures are described
from Iceland (Friedman et al., 1971) and Svalbard (Jahn, 1975, pp. 74-78, 1983). Some
transliterated Russian texts refer to these structures as “initially-ground wedges”
(Romanovskii, 1974, pp. 71-74, 1977b, 1978; Melnikov and Spesitvsev, 2000, Figure 4-25),
implying that they eventually evolve into other types of frost fi ssures. However, because
their origin is unclear, the more descriptive term “soil wedge” is preferred here. In all
cases, these cracks rarely exceed 1.5 m in depth, are fi lled with mineral soil, and usually
occur in sandy loam and gravel. Sometimes, the enclosing sediments show deformation,
often in the form of a “turning down” of the sediment layers. Relict soil wedges are dis-
cussed further in Chapter 13.
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