Geology Reference
In-Depth Information
4
Cold-Climate Weathering
Frost action in soil refers to two processes: (1) frost heave that occurs as water changes
state during the freezing period, and (2) thaw weakening and settlement that
occurs as seasonally-frozen ground thaws. Frost action in bedrock is caused by hydro-
fracturing, ice segregation, thermal shock, or a combination of these processes, and
leads to mechanical disintegration of material. Frost action is one component of cryo-
genic weathering, a poorly-understood group of physico-chemical processes that
operate in cold climates. Specifi c chemical weathering processes include salt weather-
ing, solution, and biological weathering. Cryogenic processes result in distinctive soil
morphology patterns.
4.1. INTRODUCTION
Since publication of the
Second Edition
, signifi cant advances have been made in our
understanding of periglacial weathering processes. This statement does not necessarily
imply that new and important processes have been discovered. Rather, it refl ects a cautious
and considered re-evaluation of known processes combined with a growing appreciation
that much is still unknown about the nature of cold-climate, or cryogenic, weathering. To
refl ect these changes, the title of this chapter has been modifi ed from “Frost action and
cryogenic weathering” to the more general title “Cold-climate weathering.”
This change may appear semantic but it refl ects a growing acceptance that frost action
has been overemphasized in the past and that temperature alone is not necessarily the
controlling factor in cold-climate weathering. A related assumption that is now question-
able is that cold-climate landscape modifi cation is relatively rapid. While this might be
the case in certain areas, it may also be interpreted as a refl ection of the paraglacial adjust-
ment that many landscapes are currently experiencing rather than the implied effi cacy of
frost action. In addition, it is increasingly realized that physico-chemical processes, espe-
cially those that operate at sub-zero temperatures, are far more complex, and certainly
less well understood, than traditional weathering processes.
Nevertheless, frost action remains the defi ning characteristic of periglacial environ-
ments and demands detailed consideration.
4.2. GROUND FREEZING
Frost action is a collective term used to describe a number of distinct processes which
result from alternate freezing and thawing in soil, rock, and other materials. Frost action
also refers to the effects of frost on material and structures placed on, or in, the ground.
