• Hall, K. 1990*a. Mechanical weathering rates on Signy Island, maritime Antarctic. Permafrost and Periglacial Processes, 1, 61-67.
The first two papers are extensions of the work undertaken for an M.Phil. thesis at the University of Reading. Although the papers are based upon that research undertaking, the detail and discussion extend beyond that which was presented in the final thesis. The work is incorporated here, as information pertaining to thermal conditions at a nivation site, to add to the general background regarding thermal data and also with respect to the later discussions regarding nivation and its relationship to cryoplanation (Chapter 5). Thermal data were obtained from a variety of locations (Fig. 4); information from Livingston Island, Alexander Island, Adelaide Island (Antarctica) and the Canadian Rockies are cited here but other references (e.g. Walton and Hall, unpubl., Hall, 1999a (discussed in Chapter 4), and Hall, 1991 a (given above under rock moisture data)) provide thermal data for Signy Island (Antarctica), Canada, and the Juneau Icefield (Alaska) respectively.
These data offer direct information on rock temperatures from field situations and,
in some instances (e.g. Hall, 1997a; Hall and Andre, In Press), include data at
sufficient frequency (two minutes, one minute or 30 second intervals) as to allow
evaluation of thermal stress fatigue/thermal shock. One importance of the data is
that it provides a clear manifestation that air temperatures are no surrogate for rock
temperatures. Long data records are important for indicating winter conditions
(e.g. Hall, 1997a), while data from various aspects are crucial for understanding
microclimatic variability at a site (e.g. Hall, 1998a). As fundamental as these data are, few cold region studies have obtained actual rock temperature data from the site(s) under investigation and even when these have been obtained they are frequently of short duration, of widely-spaced record intervals and do not show the spatial variability about the site. The data presented here are, so far, unique to cold region weathering studies and particularly for Antarctica.
As stated in the opening arguments, the monitoring of rock thermal conditions without a knowledge of the moisture status would not provide an adequate foundation for the evaluation of weathering, and of the role of freeze-thaw in particular. From the perspective of weathering in cold regions, no data whatsoever were available pertaining to interstitial rock water chemistry and almost none regarding rock moisture content. Thus an attempt was made to undertake monitoring of rock moisture content in the field, including its temporal and spatial variability, and to derive a method forthe determination of rock moisture chemistry.
Monitoring was undertaken primarily during the summer season (for logistical reasons) but, in one instance (Hall, 1988a), data were collected over a whole year.
In addition, on several occasions, at different work sites, short-term changes in rock moisture content were monitored via frequent observations through a 24 hr period (e.g. Hall, 1991 a). Some field data regarding rock moisture content were also obtained by means of ultrasonics (Hall, 1997a, see Fig. 5) but this was mainly restricted to laboratory undertakings (see Chapter 3).
A new technique was established for determination of interstitial rock moisture
chemistry (Hall, et al., 1986), while suggestions have also been proposed for a
number of other new methods inclUding the use of high pressure vacuum pumps
plus industrial microwave units (Hall, 1995a). As a measure of chemical
weathering, and to complement the work on the actual interstitial rock water
chemistry, work was also undertaken regarding the solutes being removed from the
weathering system (Meiklejohn and Hall, 1997). As spatially and temporally limited as these data are, when considering the complexity of cold regions, they, nevertheless, provide the first look at rock moisture chemistry and moisture content variability within the study area. In this capacity they provided the foundation for laboratory simulations and a basis for the evaluation of weathering processes operative in the study areas.
Two papers are identified as dealing specifically with rock properties, although much information on these attributes is disseminated in many of the other publications, including those dealing with laboratory simulations. The two papers cited cover the application of the stress intensity factor (K
lc),from linear elastic fracture mechanics, to determine the sort of stress required to cause rock failure, as well as the rock temperatures and crack sizes that would be necessary. This approach provides a background against which the temperature data can be evaluated, to see if temperatures sufficiently cold to cause failure actually occur.
The basis for much of the data utilised in the determination, together with further detail on porosity, permeability, frost susceptibility (S-value) and spatial variability of rock strength, was provided in Hall (1987a). Almost all the field studies cited in other chapters include some direct or indirect measures of rock properties from the field; these are complemented by the details provided in associated laboratory investigations.
The only paper dealing specifically with the determination of weathering rates is
Hall (1990a). Logistical constraints prohibited the on-going monitoring (except in
the case of Signy Island cited in Hall, 1990a) that would be required. Some papers
(e.g. Hall, 1993a. or Hall, Subm. a) provide details regarding the spatial variability
of weathering as deduced from such data as micro-indenter, Schmidt hammer
measurements, or based on taffoni sizes and frequency of occurrence, but not of
weathering rates per se. Discussion regarding weathering rates on Livingston
Island (South Shetland Islands, Antarctica) can also found in Hall, 1992a and in Hall, 1992b that are discussed in Chapter 4. The latter of the above two papers specifically deals with the difference in amount of weathering between north- and south- facing aspects.
This material thus provides a foundation of field information necessary for any
investigation of weathering in cold regions. Not only does it provide detailed data
regarding rock thermal and moisture conditions as well as information pertaining
to rock properties but it also introduces new techniques for the determination of
rock moisture chemistry. Data are provided that deal with Antarctic weathering
rates and discussion regarding the meaning of these data is given. Without such
data it would have been impossible to undertake meaningful laboratory simulations
or to provide an objective basis against which to evaluate the processes
associated with landform development in the areas studied.
Fig. 4
Collecting rock temperature data on Alexander Island (Antarctica)
Fig. 5
Collecting ultrasonic pulse velocity data in the field,
Alexander Island (Antarctica
Arctic andAlpine Research, Vo!. 12, No. 2,1980, pp. 183-194