Geoscience Reference
In-Depth Information
18
Sediment mobilisation by the wind
Giles F. S. Wiggs
18.1
Introduction
Improved understanding and measurement of aeolian
processes has allowed the development and calibration
of models of contemporary dune dynamics and distri-
bution (Andreotti, Claudin and Douady, 2002; Baddock,
Livingstone and Wiggs, 2007; Hersen, 2005; Living-
stone, Wiggs and Weaver, 2007; Parsons
et al.
, 2004;
Tsoar, Blumberg and Stoler, 2004; Walker and Nickling,
2002; Weaver and Wiggs, 2010; Wiggs, Livingstone and
Warren, 1996), which has proved essential to our inter-
pretation of palaeodune sequences (Mason
et al.
, 2004;
Stone and Thomas, 2008; Thomas
et al.
, 2000; Telfer and
Thomas, 2006), while our improved understanding of the
controls on aeolian processes has also allowed us to con-
sider the potential impact of global warming scenarios on
future dune activity (Knight, Thomas and Wiggs, 2004;
Thomas, Knight and Wiggs, 2005; Wang
et al.
, 2009).
Our understanding of aeolian processes has also been
enhanced through investigations of wind erosion from
susceptible soils and agricultural fields where models of
potential erosion, including the effects of implementing
management strategies, have been developed and cali-
brated (Buschiazzo and Zobeck, 2008; Webb
et al.
, 2009).
Previously, such models provided a fundamental frame-
work from which dust emission schemes have been de-
veloped for application to regional and global scale dust
dynamics models (Zender, Bian and Newman, 2003; Mar-
ticorena and Bergametti, 1995; Raupach, Gillette and
Leys, 1993). Finally, our application of aeolian process
understanding has progressed to extra-terrestrial surfaces
with a particular focus on the dunes and wind-streaks vis-
ible on Mars (Laity and Bridges, 2009; Kok and Renno,
2009a; Bourke, 2010; Gillies
et al.
, 2010).
Sediment movement is essentially a function of both
the power of the wind (
erosivity
) and grain characteristics
Wind can be a particularly effective medium for sediment
movement in drylands where a relatively sparse vegeta-
tion cover and thin soils combine to create highly erosive
conditions on highly erodible surfaces. There is little evi-
dence to suggest that dryland winds are any stronger than
their counterparts in humid regions, but the sparse veg-
etation cover in deserts allows the winds to contact the
surface more effectively, and the lack of root systems and
moisture to bind sediment together renders it far more
susceptible to erosion (Pye and Tsoar, 1990). The effi-
ciency of dryland winds is underlined by the continuous
advance and development of desert dunes in the Earth's
sand seas (e.g. Bristow, Duller and Lancaster, 2007), the
long-range transport of Saharan dust across the Atlantic
to the Amazon basin (Swap
et al.
, 1992), the deposition
of
400 m thick loess deposits in the Lanzhou region of
China (Porter, 2001) and the human and environmental
distress caused by agricultural wind erosion in the 1930s
Dust Bowl in mid-west USA (Worster, 1979).
To interpret the evolution of landscapes such as those
mentioned above, the processes of aeolian erosion, trans-
portation and deposition of sediment in drylands have
to be understood. Understanding of aeolian processes has
been inspired by the work of Bagnold (1941, 1953, 1956).
Indeed, no discussion of aeolian processes is complete
without reference to his north African research and much
can still be learned from these comprehensive works.
However, there has been a great deal of progression in
our comprehension in the intervening 60-70 years and an
understanding of aeolian processes has been used to clar-
ify a wide range of natural and environmental questions
and problems.
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