Weathering systems - Arid Zone Geomorphology - page 88

microclimatic fluctuations in arid environments, probably
because of cost and logistical constraints, but these have
huge future possibilities.
Monitoring of surface change can now be done using a
family of methods that build on the established and still
valuable techniques of surface profiling and the microero-
sion meter (MEM), which capture data on rock surface
topography and topographic change in a spatially lim-
ited, but quick, fashion (e.g. Stephenson et al. , 2004).
Laser scanning, optical scanning and photogrammetric
techniques can now be used to collect high-resolution to-
pographical data sets. From these, geomorphometric mea-
surements (e.g. roughness measurements) can be taken to
quantify topography at a range of scales. Furthermore,
these techniques can be used to monitor surface change
as a result of weathering - with before and after data col-
lected at very high resolution allowing detailed compar-
isons of surface topography. Most examples of their use
in weathering research so far come from laboratory-based
experimental studies (Birginie and Rivas, 2005; Bourke
et al. , 2008). However, increased portability of such sys-
tems means that they can now be used in the field even in
remote and challenging environments, while casting tech-
niques can also be used to capture topographic detail in the
field for subsequent scanning in the laboratory (Ehlmann
et al. , 2008).
A wide range of nondestructive testing methods is now
available, which can be used to survey conditions on and
within weathering rock surfaces in the field in order to in-
vestigate weathering. For example, a range of resistivity-
based techniques are available to monitor surface or sub-
surface moisture regimes within porous materials, which
help in understanding some of the key factors affecting
weathering at the small scale (Figure 6.4(b)). While such
techniques have mainly been used in mountain and built
environments, they have huge potential for helping to un-
derstand weathering in desert environments (Sass, 2005;
Sass and Viles, 2006; Mol and Viles, 2010). Although
weathering occurs at or near the surface of a rock or
mineral it is often influenced by deep-seated movements
of water and thus knowledge of conditions and mois-
ture movements under the surface is of huge importance.
Geophysical techniques such as ground penetrating radar
(GPR) have also recently been applied to understanding
the development of flaking and undoubtedly have wider
applications to weathering in arid environments (Denis
et al. , 2009). Several nondestructive techniques are also
available to monitor rock hardness in the field, which can
be used to evaluate weathering, based on the principle that
weathering will (in general) reduce the hardness of rock
surfaces. The Schmidt Hammer, Duroscope and Equotip

ing in arid and other environments (Figure 6.4(c)). These
devices are (relatively) cheap, easily portable and quick
to use; thus they are ideal for collecting large data sets
under challenging field conditions (Goudie, 2006; Aoki
and Matsukura, 2007).
Experimental studies, while not in themselves new,
have dramatically increased in number and sophistica-
tion in recent years as a result of the availability of better
equipment to control and monitor environmental condi-
tions. Environmental cabinets enable researchers to con-
trol temperature and relative humidities and cycle them,
as well as use lamps to provide radiant heating. The basic
approach of many weathering experiments of relevance
to arid environments has been to subject samples (usually
cut blocks of stone) to a weathering regime (often involv-
ing salts, moisture and temperature fluctuations) over a
period of time (Figure 6.4(d)). Assessment of weathering
has usually been made by making comparative observa-
tions of shape, size, weight, surface topography, strength
and so on, before and after (and sometimes during) the ex-
periment (see, for example, Goudie, 1986; Robinson and
Williams, 2001; Goudie, Wright and Viles, 2002; Elliott,
2008). Smith et al. (2005) write perceptively about the
problems of many such weathering experiments. Flaws
within experimental designs used and limitations of avail-
able simulation chambers mean that it is very difficult
to link results from experiments to real-world conditions.
Increased realism has recently been brought into exper-
iments of arid weathering systems through the use of
pre-treated blocks to simulate an inherited 'weathering
history' (Warke, 2007). Thus, progress is being made in
bridging the gap between the field and the laboratory.
Weathering experiments that are highly limited in spa-
tial and temporal scale also raise problems. Thus, we
cannot expect too much of them in terms of contribut-
ing to questions about weathering systems over large
spatial scales and long time scales. Furthermore, most
arid weathering experiments have been of intermediate
to high complexity - and perhaps the time is now right
for more simple experiments, linked to the development
of computer-based models, to allow the development of a
better understanding of what is really happening in weath-
ering. An example is the use of environmental scanning
electron microscopy (ESEM) to simulate the behaviour
of salt solutions and small samples of salt-affected stone
under very simple regimes (Doehne, Carson and Pasini,
2005). The fact that the ESEM allows us to view the
changes as they occur means that we can, at last, watch
weathering happen! On the other hand, weathering ex-
periments can also usefully become more complex and
more realistic, and here the use of field experiments is