Introduction - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 12

Fig. 1.17 An image of the Grand Erg Orientale (part of the Sahara) in
Algeria, taken through the window of the International Space Station.
The overall arrangement is clearly linear, but the crestlines are star-
shaped. Are these linear dunes that have been morphed into star

shapes, or are they star dunes that just happen to have formed in lines?
The linear dunes are about 2 km wide. Image Science and Analysis
Laboratory, NASA-Johnson Space Center. ''The Gateway to Astronaut
Photography of Earth''

buildings over some decades. Migrating dunes can block
roads, railways or canals, requiring expensive mitigation; on
the larger scale, the burial of fields or oases by dunes can
simply force us to migrate ourselves, admitting defeat against
the onslaught of sand. In fact, the battle of arid lands ecolo-
gists against dunes in Oregon inspired the science fiction
author James Herbert to write his iconic Dune novel, and
dunes feature on a number of fictional worlds (Fig. 1.16 ).
Our aim in this topic is to survey the physical principles
behind dunes, review observations and measurement tech-
niques, emphasizing the newest developments, and to draw
together what has become known about dunes on other
planetary bodies with what has been learned about the
Earth. Just as dunes are a feature of the interface between
the ground and the air, so studies of dunes have fallen across
the domains of geography, physics, geomorphology, geo-
chemistry, planetary science and other fields. We hope the
reader enjoys the adventure, as we have, of straying beyond

the traditional bounds of whatever discipline they consider
themselves in. This is not a textbook, merely a travel guide.
Our goal is to provide breadth, and to identify pathways in
data, techniques and the literature for the reader to wade in
as deeply as they wish.
We have organized the topic in five main sections. First is
the introduction you are now reading. In the second section,
we describe the principal physics behind dunes, what they are
made of, and what controls their size, shape and movement.
Next, we discuss the aeolian features seen on various dune
worlds, namely Earth, Mars, Titan and Venus, as well as the
possibility for bedforms on a few other planetary bodies. The
fourth section discusses the various ways in which dunes are
studied: in the laboratory or wind tunnel, in the field, and by
computer simulation. The various remote sensing techniques
applied to aeolian studies are also reviewed. Lastly, we sur-
vey why dunes and related landforms and processes are
important—as physical systems, as environmental