1. School of Earth Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
2. Desert Research Institute, UCCSN, 2215 Raggio Parkway, Reno, Nevada 89512 , USA

Correspondence to: C. S. Bristow¹ Correspondence and requests for materials should be addressed to C. S. B. (e-mail: Email: c.bristow@bbk.ac.uk).

Abstract

Linear sand dunes—dunes that extend parallel to each other rather than in star-like or crescentic forms—are the most abundant type of desert sand dune¹. But because their development and their internal structure are poorly understood, they are rarely recognized in the rock record². Models of linear dune development^{2, 3, 4, 5, 6} have not been able to take into account the sub-surface structure of existing dunes, but have relied instead either on the extrapolation of short-term measurements of winds and sediment transport or on observations of near-surface internal sedimentary structures. From such studies, it has not been clear if linear dunes can migrate laterally^{2, 7, 8}. Here we present images produced by ground penetrating radar showing the three-dimensional sedimentary structure of a linear dune in the Namib sand sea, where some of the world's largest linear dunes are situated. These profiles show clear evidence for lateral migration in a linear dune. Moreover, the migration of a sinuous crest-line along the dune produces divergent sets of cross-stratification, which can become stacked as the dune height increases, and large linear dunes can support superimposed dunes that produce stacked sets of trough cross-stratification. These clear structural signatures of linear dunes should facilitate their recognition in geological records.