Dune Fields, Sand Seas and Transport Pathways - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 99

Fig. 8.1 An image from the
International Space Station,
looking roughly north, showing
Great Sand Dunes National Park
and Preserve. The sand is sourced
from rivers to the west, and is
topographically trapped by the
dark Rocky Mountains. Compare
with sand trapped on Mars by
crater walls (Fig. 18.16 ). Frame
ISS016E006986, taken with
800 mm lens (NASA/JSC)

(2008). The sand texture is also diagnostic, in that rounded
and fine sands are likely to have been transported further.
For Mars, we are forced to rely on what composition can
be inferred spectroscopically from orbit, and from geomor-
phology. For example, the orientation of dunes can be used
to infer the sand transport direction. Some global studies
have been made since the Viking era (e.g., Breed et al.
1979). The only very prominent sand accumulation obvious
in that data was the north polar erg, Olympia Undae (e.g.,
Tsoar et al. 1979). The dunes are dark, suggesting a basaltic
composition, although they also contain gypsum, which may
indicate evaporite deposits as a source for some material. No
specific source region has been identified for Olympia,
although it may be that sand comes from everywhere. A
numerical experiment (Anderson et al. 1999) of putting sand
all over Mars and observing where it migrated due to winds
simulated in a general circulation model ( Chap. 19 ) noted
that sand accumulated in the northern polar erg.
The growing body of data from Mars missions has now
permitted some regional and local studies. Fenton (2005)
considered the dunefields (mostly on the floors of impact
craters) in the Noachis Terra region in the southern high-
lands, suggesting that most of the sand must be sourced
locally, since large-scale transport patterns were not visible.
Silvestro et al. (2010b) have studied six dark dune fields in
Aonia Terra in the eastern Thamasia region of Mars and
have attempted to interpret the sand transport pathways and
sources from imaging and topography data.
For Venus, there is not much to say given the present
meager dune inventory: the sand source is probably the
limiting factor in dune formation and is probably local to

Fig. 8.2 Victoria Crater on Mars, imaged from orbit. This crater is
800 m in diameter, and sports a network of duneforms on its floor.
This crater is particularly well-studied, as the Opportunity rover drove
around part of it. Note the dark streaks emanating from the crater,
suggesting that material weathering out of the crater walls is being
transported away. HiRISE image, credit NASA/JPL/U.Arizona

the sand ( Chap. 2 ) can be evaluated to match candidate source
regions, such as the study of southwestern USA dune sands
and the role of the Colorado river in providing the source
(Muhs et al. 2004), or the Rub' Al Khali study by Besler