Geology Reference
In-Depth Information
A number of frost-action processes operate in the near-surface layer subject to seasonal
thaw (the active layer), the near-surface permafrost located above the depth of zero-
annual amplitude, and the zone of seasonal freezing and thawing in non-permafrost
regions. These processes include moisture migration within frozen ground and those
associated with repeated freezing and thawing (soil churning or cryoturbation, frost creep,
solifl uction and gelifl uction, the upfreezing of stones, and particle-size sorting).
1.5.2. Azonal Processes and Landforms
A number of important periglacial processes center upon the seasonal freezing of soil and
bedrock. These include the weathering of rock by either mechanical (frost) wedging or
the complex of physical, biochemical or physico-chemical processes. Better known are
those associated with running water, wind, snow, and waves, all of which assume distinc-
tive characteristics under cold-climate conditions.
Some azonal processes are of especial interest to periglacial geomorphologists. For
example, snow is an important source of moisture and an abrasive agent at low tempera-
tures. Furthermore, it can act as a local source of soil moisture for ground heaving and
frost action. Wind is also of special interest to periglacial geomorphology because the
paucity of vegetation in cold regions provides wind with important erosional and trans-
portational abilities. Finally, sea ice and river ice (commonly referred to as “ice-infested
waters”), by restricting the time duration of wave action and/or open-channel fl ow, and
through ice-pushing, ice-jams, and other impacts, can produce relatively distinct coastal,
river channel, and lake conditions.
One aim of geomorphology is to create models of landscape evolution. These embody
assumptions as to the processes involved, their speed of operation, and the manner in
which surface morphology changes. In the case of periglacial geomorphology, the peculi-
arities of frozen ground and intense frost action impart a unique landform response. For
example, slopes that are frozen, or are thawing, experience relatively unusual conditions
associated with pore-water expulsion and thaw consolidation. These may promote mass
failures that are distinct from the more well-known failures that occur on slopes that
evolve under non-frozen conditions.
1.5.3. Paleo-Environmental Reconstruction
The growth of cryostratigraphy, when combined with the increased sophistication of
Quaternary science, is largely replacing traditional Pleistocene periglacial geomorphology
as a component of modern periglacial geomorphology. Morphological and stratigraphic
evidence is now interpreted within the context of a more realistic appreciation of perma-
frost terrain and its climatic signifi cance combined with, and constrained by, the use of
isotopic and other absolute dating techniques and by proxy data sets.
1.5.4. Applied Periglacial Geomorphology
Many components of periglacial geomorphology are of applied signifi cance and have
societal relevance. For example, the periglacial environments of the world are home to
over nine million people, mostly in northern Russia and Eurasia, and their health and
economic well-being are of concern. The provision of water, municipal services, housing,
roads, and other forms of infrastructure must take into account the nature of the cold-
