Geology Reference
In-Depth Information
13.2. INTENSE FROST ACTION
13.2.1. Soil Wedges
The occurrence of soil wedges (“ground wedges” or “initially-ground wedges”) that result
from seasonal-frost cracking has already been discussed (see Chapter 6). Their occurrence
implies deep seasonal-frost penetration. The Russian literature recognizes a range of
forms (Figure 13.1). Although seasonal-frost cracking has been reported from several
non-permafrost regions (Svensson, 1983, 1988b; Washburn et al., 1963), there are few
descriptions of relict soil wedges in mid-latitudes in the North American and European
literature. Brief observations made by French et al. (2003, pp. 267-268) for Southern New
Jersey, Eastern USA, suggest they can be distinguished from sand-wedge casts by their
younger stratigraphic position and by their shape, size, and spacing. They are broad
structures, usually less than 2.0 m deep and between 20 cm and 60 cm wide, spaced approx-
imately 2.0 m to 3.0 m apart, and fi lled with locally-derived mineral soil of a primary
nature. It is speculated that they formed under conditions of deep seasonal frost that
occurred when permafrost degraded towards the end of the Late Pleistocene. Their rec-
ognition is diffi cult because of the effects of agricultural practices (plowing, post holes,
service lines etc.).
It is likely that some of the wedge structures reported from elsewhere in the mid-
latitudes (Chapter 11) may refl ect deep seasonal frost rather than permafrost.
13.2.2. Frost-Disturbed Bedrock
Mechanically-weathered bedrock is often interpreted to refl ect intense frost action. As
discussed earlier in Chapter 4, frost action can imply several different mechanical weather-
ing processes. For example, rock may be shattered by the downward infi ltration of water,
and its subsequent freezing, in cracks and interstices. Rock shattering may also result from
Figure 13.1.
Different types of soil wedges (“initially-ground wedges”) described in the Russian
literature. Legend: 1, soil/humus; 3, sand and gravel; 4, loess-like deposits; 5, peat; 6/7, boulders and
pebbles; 8, stratifi cation and small faults; 9, ground wedges; 10, permafrost table. From Romanovskii
(1973), Melnikov and Spesivtsev (2000).
