Geology Reference
In-Depth Information
Table 4 . 8.
Chemical changes observed following repeated freezing and thawing of clay minerals.
Mineral
Number of freeze-thaw
Content (mmol/100 g)
cycles
Na
+
K
+
Ca
2+
Kaolinite
0
0.08
0.19
13.86
100
0.20
-
11.65
Bentonite
0
8.26
6.00
44.22
100
15.66
0.38
47.53
Polymineral clay
0
0.16
0.13
57.42
100
6.00
0.64
75.25
Source: Datsko and Rogov (1988).
Ground surface
Ice lensing, and soil freezing
Concentration of
solutes
Upward
movement of
solutes
Void
Active
layer
Permafrost
table
Freezing front
Permafrost
Freezing, of
near-surface
with ice
lensing
Zone of solute
concentration
Crystalline
coating, beneath
stone
Direction of
freezing
Direction of
solute movement
Upward heave
('Frost-pull' or
'Frost-push')
Figure
4.13.
The probable mechanism of solute precipitation by freezing. As the freezing front
progresses downwards, it attracts solutes from the active layer that concentrate beneath coarser
particles. Modifi ed from Vogt and Corte (1996).
A third example concerns anomalous micro-erosional phenomena that occur in some
of the cold deserts of Antarctica. Their mechanics of formation are unclear. For example,
grooves, pits, and furrows (“pseudo-rinnenkarren”) have been described from several
localities (French and Guglielmin, 2002a, b; Richter, 1985). In Northern Victoria Land,
the grooves are developed on steeply inclined (
35°) biotite-monzogranite bedrock sur-
faces. They are generally straight, 10-30 cm deep, 20-80 cm in width, and up to 10 m in
length. Many join and bifurcate and others meander, all with no apparent structural
control. One possible explanation is snowmelt erosion at sub-zero temperatures, together
with prior granular disintegration. Rock varnish on adjacent surfaces suggests a chemical
or biogeochemical origin, perhaps aided by wind (Campbell and Claridge, 1987, pp. 124-
129; Dorn and Oberlander, 1982; Dorn et al., 1992) but similar, and equally puzzling,
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