Cold-Climate Weathering - The Periglacial Environment - page 60

the opening of joints, and the frequency of rockfall in sedimentary rocks. For example,
in the Japanese Alps, joint widening occurs in both autumn and spring. The autumn
events are associated with freeze-thaw cycles, and the magnitude of the widening refl ects
freezing intensity and water availability. By contrast, widening in spring likely originates
from refreezing of melt water entering the joint. In the high-latitude environment of
Svalbard, there was little evidence for thermal-stress fatigue. Instead, when high moisture
content was associated with freezing conditions, this favored rock disintegration. Frost
shattering acted by wedging along bedrock joints and cracks. Similar conclusions were
reached earlier by L. Dredge (1992) when describing the disintegration of limestone
bedrock in the eastern Canadian Arctic. Joints and weaker bedding allow water infi ltra-
tion and provide sites for fracturing by volumetric expansion, either in open-system or
closed-system environments, or by hydraulic freeze-back processes. Joint expansion may
also cause the upward buckling of slabby limestone along joint lines.
In a series of experiments, V. N. Konishchev and V. V. Rogov (1993) found that the
speed of crack growth in water (ice)-saturated samples far exceeded that of dry samples
when subject to numerous freeze-thaw cycles. These data (Table 4.2A), compiled for dif-
ferent rock types, give some indication of the approximate maximum speed of frost
weathering. The average thickness of the disintegration layer for ice-saturated rocks during
one freeze-thaw cycle ranged from a high of 3.5 mm in marl to a low of 30-50 10 −5 mm

×

Table 4 .2 . Some Russian data concerning rates of bedrock weathering by frost action: (a) average
thickness of disintegration layer for one freeze-thaw cycle in various rocks of different water
saturation; (b) data on fi ssuring of feldspar sandstones in an opencast mine, Taimyr, Siberia.

(A) Average Thickness of Disintegration Layer (mm)

Rock, deposits Dry Samples Water-saturated Samples

Range (mm) Average (mm) Range (mm) Average (mm)

Granite (6.4-8.6) × 10 −5 8.0 × 10 −5 (6.4-34.9) × 10 −5 14. 5 × 10 −5

Weathered granite (8.7-11) × 10 −5 10 × 10 −5 (10 -32) × 10 −5 20 × 10 −5

Gneiss-granite, gneiss (7.0-9.2) × 10 −5 8.0 × 10 −5 (7.0-9.9) × 10 −5 9.0 × 10 −5

Porphyry (8.1-25) × 10 −5 11 × 10 −5 (3.1-92.4) × 10 −5 30 × 10 −5

Diabase (0.8-8.3) × 10 −5 4.5 × 10 −5 (1.1-8.3) × 10 −5 4.5 × 10 −5

Metamorphic shale (2.8-27) × 10 −5 12 × 10 −5 (8-35) × 10 −5 18 × 10 −5

Limestone (3.8-7.3) × 10 −5 5.5 × 10 −5 (22.3-24.7) × 10 −5 23.5 × 10 −5

Sandstone (4.0-7.1) × 10 −5 6.0 × 10 −5 (4.0-160) × 10 −5 48 × 10 −5

Limestone, dolomite (400-1000) × 10 −5 600 × 10 −5 1-8.7 1.0

Marl (400-1000) × 10 −5 600 × 10 −5 1-8.7 3.5

(B) Fissures Year of Open-pit Width of Fissures (mm)

Stripping

Min. Max.

Horizontal 1973 15 1

1977 18 0.5

Vertical and subvertical 1973 50 3

1970 60 1

Source: Konishchev and Rogov (1993). Reproduced by permission of John Wiley & Sons Ltd.