Geology Reference
In-Depth Information
below 0 °C, with particular reference to those subject to intense frost action, and to soils
overlying permafrost. The term “cryosol,” fi rst coined by N. Federoff (1966), is now
widely accepted (Kimble, 2004). Furthermore, a Cryosolic Order, initially developed in
Canada (Canada Soil Survey Committee, 1978; Soil Classifi cation Working Group, 1998),
is gaining acceptance in the soil-science community.
In spite of early studies by Russian and German pedologists (Dokuchaev, 1900;
Meinardus, 1912, 1930), study of the soils of cold regions was neglected for many years.
This was because these soils are generally shallow, lack well-defi ned soil profi les, and are
characterized by instability of the mineral soil, the result of frost action. Soil-horizon
designation was often elementary, diffi cult, and unsatisfactory. Traditionally, these soils
were described in the context of their relation to the major vegetation zones of the world
(Hill and Tedrow, 1961; Tedrow, 1977).
4.9.1. Cryosols
A cryosol is defi ned as “soil formed in either mineral or organic materials having perma-
frost either within 1 m below the surface or, if the soil is strongly cryoturbated, within 2 m
below the surface, and having a mean annual ground temperature below 0 °C” (van
Everdingen, 1998). Cryosols are of three types (Table 4.9). Static cryosols develop prima-
rily in coarse-textured mineral parent material, where cryoturbation and small-scale pat-
terned ground phenomena are largely absent. Turbic cryosols show marked evidence of
cryoturbation within the active layer (i.e. disrupted, mixed, or broken horizons and dis-
placed material). Organic cryosols develop in organic material containing more than 17%
organic carbon by weight and where permafrost is usually less than 1 m from the ground
surface. Common landforms associated with organic cryosols include palsas, peat poly-
gons, and high-centered polygons.
Table 4 .9.
Summary of the nature of materials, degree of cryoturbation, and depth to
permafrost of the major cryosolic soils.
Parameter
Cryosolic Great Groups
Turbic Cryosol
Static Cryosol
Organic Cryosol
Soil material
Mineral
Mineral
Organic
Cryoturbation
Marked: usually patterned ground
None
Uncommon
Permafrost
Within 2 m of surface
Within 1 m of surface Within 1 m of surface
N.B. A more detailed description of turbic cryosols, static cryosols, and organic cryosols is given in
Tarnocai (2004a, tables 5.1-5.4, pp. 607-609).
The pedon, the basic soil unit, is the three-dimensional unit by which cryosolic soils
are described. The pedon is also a geomorphological concept because it allows one to
consider the numerous small-scale patterned ground phenomena that typify many per-
iglacial landscapes. The pedon of a non-sorted circle, the most widespread of all small-
scale patterned ground forms, is illustrated in Figure 4.14. In the case of low- and
high-centered polygons, one pedon would characterize the polygon trench area while a
second would characterize the central part of the polygon (Tarnocai, 2004a, p. 600). The
various horizon designators for cryosolic soil description, as identifi ed in the Canadian
System of Soil Classifi cation (Soil Classifi cation Working Group, 1998), need not concern
us here and are summarized in Tarnocai (2004a, pp. 605-607).
