Geoscience Reference
In-Depth Information
23
Geomorphological hazards in drylands
Giles F. S. Wiggs
23.1
Introduction
does not have to be the result of human activity since ge-
omorphological processes naturally operating in drylands
can generate similar consequences (Prospero, 1999), as
illustrated by the close correlation found between deposi-
tion of Saharan dust in Spain and daily mortality (Perez
et al.
, 2008). Further, environmental changes as a result of
global warming may induce regional-scale remobilization
of currently stable and habitable dunefields, so threatening
livelihoods and food security at a national scale (Thomas,
Knight and Wiggs, 2005; Wang
et al.
, 2009).
This chapter reviews the most frequently occurring haz-
ards originating from human interaction with both aeolian
and fluvial processes in drylands and, where appropri-
ate, outlines some of the commonly employed methods
by which the impacts of such hazards may be reduced.
Hazards associated with these processes have been cho-
sen for review because they have been the focus of the
majority of research effort in recent years. Salt weathering
of buildings and roads is not considered here as research
into this hazard has declined since the 1990s (although
see Goudie and Viles, 1997, for a review) and salinization
of soil as a hazard is covered elsewhere in this topic (see
Chapter 22).
With more than 1 billion people estimated to be living
in dryland zones (Middleton and Thomas, 1997) it is
inevitable that the activities of human populations fre-
quently overlap with the operation of geomorphological
processes. While such interaction may often have negli-
gible consequences, our increasing experience of living
in drylands and utilising their resources has shown that
there are specific circumstances where the interface be-
tween human activity and geomorphological dynamism
can prove particularly hazardous. Such hazards can be
distinguished by their two differing principle causes:
Human activity encroaching into areas of highly active
geomorphological processes (e.g. construction of urban
settlements on the piedmonts of desert mountains with
a significant flood risk; Rhoads, 1986).
Human activity accelerating geomorphological pro-
cesses in otherwise stable landscapes (e.g. agricultural
wind erosion in the Dust Bowl of the mid-west USA;
Worster, 1979).
23.2
Aeolian hazards
The large range in scale of the effects of dryland geo-
morphological hazards is also of note. While construction
of communication lines to service the oil industry in the
Middle East may cultivate small and site-specific (though
intense) hazards due to sand encroachment over roads and
railways (Dong
et al.
, 2004; Zhang
et al.
, 2007), dust gen-
eration as a result of the draining of inland water bodies
in drylands (e.g. Owens Lake in California - see Chap-
ter 15) can result in very large off-site pollution hazards,
sometimes well beyond the boundaries of drylands them-
selves (Gill, 1996). Such large-scale and off-site pollution
23.2.1
Blowing sand and active dune movement
As noted in Chapter 18, where sediment is freely avail-
able and the erosivity of the wind exceeds the resistance
of the sediment, sand will become entrained and trans-
ported by the windflow. While blowing sand itself can be
hazardous to human activity by undermining structures,
sand-blasting surfaces and depositing on roads and rail-
ways (Watson, 1985, 1990), further hazards result from
