Geoscience Reference
In-Depth Information
(a)
Dominant transport
Gross bedform
normal transport
Resultant transport
Dune trend
Subordinate
transport
(b)
180
160
140
120
100
80
60
Crescentic
40
Linear
Star
20
0
0
20
40
60
80
100
120
140
160
180
Dune trend
Figure 19.22
Gross bedform normal (GBN) transport direction and dune trends: (a) explanation of the gross bedform normal
model (after Rubin and Ikeda, 1990); (b) relations between dune trend and GBN direction (after Lancaster, 1991, with additional
data).
(Bristow, Duller and Lancaster, 2007; Kocurek
et al.
,
1991; Lancaster
et al.
, 2002), so age of the megadunes
is also an important factor.
relative to the resultant or vector sum of sand transport
(Fryberger, 1979). Thus dunes can be classified as trans-
verse (strike of crestline approximately normal to resul-
tant), longitudinal (crest parallel to resultant) or oblique
(15-75
◦
to resultant direction) (Bagnold, 1953; Glennie,
1970; Hunter, Richmond and Alpha, 1983; Mainguet and
Callot, 1978).
Field and laboratory experiments with wind ripples and
subaqueous dunes (Rubin and Hunter, 1987; Rubin and
19.7.6
Dune trends
The factors that determine the alignment of dunes with re-
spect to the wind have long been a subject for speculation.
