Geoscience Reference
In-Depth Information
Weathering systems
Heather A. Viles
6.1
Introduction
landforms, and also contribute to the evolution of land-
scapes more generally through the generation of sediment
and shaping of relief. However, despite much recent re-
search progress, three major challenges remain for scien-
tists studying desert weathering systems: i.e. to explain
the genesis of some enigmatic desert weathering land-
forms, to ascertain the tempo of weathering processes
in dryland environments and to elucidate the contribu-
tion that weathering makes to overall landscape evolution
within drylands. Looking at the first of these challenges,
Figure 6.2 illustrates some of the unusual and complex
weathering features characteristic of arid environments.
There are still no general theories for the development
of many of these weathering features such as alveoli and
tafoni, despite a wealth of testable hypotheses and a wide
range of empirical studies from many dryland areas. It is
still unclear whether any weathering features are found
uniquely in arid environments or, indeed, to what extent
they are purely weathering features or influenced by other
geomorphic processes.
The second challenge for scientists, measuring rates
of weathering, has been the subject of debate since the
earliest days of desert geomorphology. Workers such as
Peltier in the 1950s believed that desert environments were
characterised by extremely low rates of weathering, while
from the 1970s and 1980s onwards, scientists such as An-
drew Goudie pioneered the view that some desert areas
are weathering 'hot spots' with very high rates (Goudie
and Watson, 1984). Problems of quantifying weathering
rates meaningfully over short and long timespans, cou-
pled with the diversity of desert conditions, means that
this debate still rages. Difficulties in addressing the first
two challenges means that we are still a long way from
overcoming the third challenge of understanding the over-
all contribution of weathering to landscape evolution in
Weathering is a very neglected part of the geomorphic
system in all environments. While in comparison with
other Earth surface processes weathering is often slow
and hard to discern, it is undoubtedly a key influence on
landscape development in two main ways, i.e. through
its production of individual (often small-scale) landforms
and through its contribution to overall denudation rates.
The 'holy grail' for weathering geomorphologists is to
understand these two influences and how they might be
linked to one another. Arid environments provide an ex-
treme case of the interactions between weathering and
geomorphology, and are thus of particular interest. It is
noticeable that most scientists who study weathering in
arid environments also do so in a range of other envi-
ronments; thus there is much cross-fertilisation of ideas
based on comparisons of weathering systems in differ-
ent climatic zones. While weathering systems (which can
be defined as the two-way, complex and emerging inter-
actions between weathering processes and the materials
on which they operate) in arid environments do not per-
haps have the immediate visual appeal of aeolian systems
(especially as manifested through extensive dunefields)
or fluvial systems (such as networks of wadis), they are
at the heart of some exceptionally beautiful (and often
highly valued) landscapes (Figure 6.1). The intensely dis-
sected and finely sculpted sandstone outcrops of Utah in
the USA, the Wadi Rum area in Jordan and the Acacus
Massif in Libya, for example, all demonstrate the dis-
tinctive and often enigmatic role of weathering in arid
environments.
Within arid environments, there is general agreement
that weathering processes are involved in the produc-
tion of a range of intriguing small- and medium-scale
