Geoscience Reference
In-Depth Information
5.2.1
Frost Heaving
Frost heaving refers to rise of the ground surface or of coarse fragments due to
volumetric expansion of water during the formation of segregation ice. Key mecha-
nisms are needle-ice formation and cryoturbation (Sect.
5.2.3
). Large pressures
may build up during heaving that have a major impact on structures. French (
2007
)
reported values for frost heaving that included 1.5-14 cm/year for arctic regions,
2-30 cm/year for alpine regions, and 0.4-4.0 cm/year for Antarctica.
5.2.2
Freeze-Thaw Cycles
Repeated cycles of freezing and thawing of water in the soil are responsible for
frost heaving of coarse materials, cryoturbation, and mechanical or cryoclastic
weathering. During “freeze-back”, the freezing fronts move both from the soil sur-
face downward and the permafrost table upward. As this happens, moisture is
removed from the unfrozen soil material between the two fronts (cryodesiccation).
French (
2007
) reported numbers of freeze-thaw cycles (surface or 1-2 cm depth)
that included from 23 to 94 in the Arctic, 9 to 50 in alpine regions, and 19 to 42 in
Antarctica.
5.2.3
Cryoturbation
Cryoturbation is often recognized as the most important cryopedologic process in
cryosols (Tedrow
1962
; van Vliet-Lanoë
1988
; Bockheim and Tarnocai
1998
;
Bockheim et al.
1998a
; Bockheim
2007
; Jelinski
2013
). Cryoturbation is a collec-
tive term used to describe all soil movements due to frost action. Cryoturbation is
evidenced by (1) irregular horizons, (2) deformation of textural bands from deposi-
tion in the parent material, (3) broken horizons, (4) involutions, (5 the accumulation
of fi brous or partially decomposed organic matter concentrated in the transition
zone or on top of the permafrost table, (6) oriented coarse fragments, (7) silt caps
from vertical sorting, and (8) upwarping of sediments adjacent to sand- or ice-
wedges (Fig.
3.1
)
.
Cryoturbation is a complicated process that involves winter freezing of the active
layer that enables ice lenses to form accompanied by loss of water from the adjoin-
ing soil and summer thawing resulting in subsidence and dilation (Fig.
5.3
).
Although this model was developed by Mackay (
1980
) to explain the formation of
earth hummocks in arctic Canada, it illustrates the cryoturbation process. Examples
of cryoturbation in cryosols are shown in Fig.
5.4
.
