Geomorphology of desert sand dunes: A review of recent progress Ian Livingstone a, ⁎ , Giles F.S. Wiggs b , Corinne M. Weaver b a School of Applied Sciences, The University of Northampton, Northampton NN2 7AL, UK b Oxford University Centre for the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK Received 6 April 2006; accepted 29 September 2006 Available online 30 November 2006 Abstract Through the 1980s and 1990s studies of the geomorphology of desert sand dunes were dominated by field studies of wind flow and sand flow over individual dunes. Alongside these there were some attempts numerically to model dune development as well as some wind tunnel studies that investigated wind flow over dunes. As developments with equipment allowed, field measurements became more sophisticated. However, by the mid-1990s it was clear that even these more complex measurements were still unable to explain the mechanisms by which sand is entrained and transported. Most importantly, the attempt to measure the stresses imposed by the wind on the sand surface proved impossible, and the use of shear (or friction) velocity as a surrogate for shear stress also failed to deliver. At the same time it has become apparent that turbulent structures in the flow may be as or more important in explaining sand flux. In a development paralleled in fluvial geomorphology, aeolian geomorphologists have attempted to measure and model turbulent structures over dunes. Progress has recently been made through the use of more complex numerical models based on computational fluid dynamics (CFD). Some of the modelling work has also suggested that notions of dune ‘equilibrium’ form may not be particularly helpful. This range of recent developments has not meant that field studies are now redundant. For linear dunes careful observations of individual dunes have provided important data about how the dunes develop but in this particular field some progress has been made through ground-penetrating radar images of the internal structure of the dunes. The paradigm for studies of desert dune geomorphology for several decades has been that good quality empirical data about wind flow and sand flux will enable us to understand how dunes are created and maintain their form. At least some of the difficulty in the past arose from the plethora of undirected data generated by largely inductive field studies. More recently, attention has shifted–although not completely–to modelling approaches, and very considerable progress has been made in developing models of dune development. It is clear, however, that the models will continue to require accurate field observations in order for us to be able to develop a clear understanding of desert sand dune geomorphology. © 2006 Elsevier B.V. All rights reserved. Keywords: aeolian; geomorphology; dune; transverse dune; linear dune; turbulence 1. Introduction Although reviews of the geomorphology of desert sand dunes routinely start with reference to the work of Ralph Bagnold (e.g. 1941), Bagnold's work concentrat- ed largely on the physics associated with the movement of individual sand grains in the wind rather than on the development of landforms. His work was ground- breaking in providing systematic empirical measure- ments of wind flow, particularly velocity profiles, and of sand flux, but his work on dunes was rather more descriptive and often speculative. A significant Earth-Science Reviews 80 (2007) 239 – 257 www.elsevier.com/locate/earscirev ⁎ Corresponding author. Fax: +44 1604 720636. E-mail address: ian.livingstone@northampton.ac.uk (I. Livingstone). 0012-8252/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.earscirev.2006.09.004