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Fig. 5.3 A model illustrating cryoturbation during growth of an earth hummock in arctic Canada
(Mackay 1980 )
5.2.4
Dilatancy
In the literature there is confusion among the terms dilatancy and thixotrophy
(Alexander 1992 ) and liquefaction. Dilatancy is defi ned as the property of dilating
or expanding, particularly in granular materials that expand due to the increase in
space between rigid particles upon displacement of the particles. In contrast, thixot-
rophy is defi ned as the property of certain gels becoming fl uid when agitated and
reverting back to a gel when left to stand. Soil liquefaction is the phenomenon
whereby a saturated or partially saturated soil substantially loses strength and stiff-
ness in response to an applied stress, often during an earthquake. Bockheim et al.
( 1998b ) observed that the Bg horizon of soils in moist nonacidic tundra often dis-
played dilatancy due to the abundance of silt and water in the active layer.
5.2.5
Cryodesiccation
The primary evidence for cryodesiccation is the presence of cracks that often extend
from the soil surface through the active layer into the near-surface permafrost.
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