Geoscience Reference
In-Depth Information
8
Desert dunes
At times, especially on a still evening after a windy day, the dunes emit,
suddenly, spontaneously, and for many minutes, a low-pitched sound so
penetrating that normal speech can be heard only with difficulty.
R.A. Bagnold (
1896
-
1990
)
The Physics of Blown Sand and Desert Dunes
(1941, p. xxi)
8.1 Introduction
Dunes are widely regarded as the quintessentially diagnostic desert landform
(
Figure 8.1
) and have attracted rather more attention than other far more extensive and
often potentially more informative desert landforms, such as mountains, pediments,
gravel plains, lake basins, alluvial fans and river sediments (Bagnold,
1941
; Monod,
1958
; Mabbutt,
1968
; Cooke and Warren,
1973
; McKee,
1979
; Wasson,
1984
;Lan-
caster,
1989
; Thomas,
1989
; Pye and Tsoar,
1990
; Yang,
1991
;Cookeetal.,
1993
;
Pye and Lancaster,
1993
; Abrahams and Parsons,
1994
; Lancaster,
1995
; Thomas,
1997
; Alsharan et al.,
1998
; Goudie et al.,
1999
; Parsons and Abrahams,
2009
;Yang
et al.,
2011a
;Yangetal.,
2011b
; Warren,
2013
). One reason for this emphasis stems
from the extraordinary variations in dune morphology, dune height and dune length,
ranging from linear dunes that extend unbroken for hundreds of kilometres to small
fields of crescentic barchan dunes advancing downwind to complex individual star
dunes that in the Namib Desert are up to 300 m high and in the Badain Jaran Desert
of Inner Mongolia attain relative elevations approaching 460 m (Yang et al.,
2011a
).
A second reason is that certain dune forms very closely reflect the direction of the
dominant sand-transporting winds. For example, linear dunes appear to run more or
less parallel to the dominant sand-moving winds, while the horns of barchan dunes
are elongated downwind and parallel to the orientation of the main sand-transporting
winds. Given an adequate sand supply and suitable winds, barchans may develop into
linear dunes (
Figure 8.2
). A third reason why dunes have attracted such attention is
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