DISTRIBUTION OF SAND DUNE SPACING, CREST LENGTH, AND DEFECT DENSITY IN SIMPLE, COMPOUND, AND COMPLEX DUNE FIELDS

Many modern sand seas display compound and complex dune morphologies, which create some of the most interesting and least understood patterns in nature. Typically these dune fields display a range of dune spacing, crest length, and defect density spanning several orders of magnitude. The aim of this study is to quantify the distribution of these parameters in simple, compound and complex dune fields and understand the cause of these distributions. Several thousand measurements of sand dune spacing, crest length and defect density were measured on Landsat 7 ETM+ satellite imagery and Digital Ortho-Photo Quarter Quadrangles (DOQQs). Measurements were taken from White Sands, Algodones, Grad Desierto, Mauritania and Namibia. The measurements were plotted to show the distributions of spacing, crest length and defect density for each dune field. In dune fields with simple morphologies a single population is observed. In all dune fields that exhibit compound or complex morphologies, multiple populations in the distribution plots are observed. In one case, these different populations may just represent compound/complex bedforms and not distinct generations of dune activity in the dune field. However, in the Azefal, Agnetir, and Akchar Sand Seas of Mauritania, which display compound linear dune morphology, the distribution plots show three distinct populations, each representing the distribution of three dune trend classes with their own characteristic spacing, crest length and defect density. The different dune trend classes have been OSL dated and shown to have formed at different periods over the last 30 ka (Lancaster et al, 2002). The distributions of dune crest length, spacing, and defect density are characteristic of the different generations of dunes in Mauritania. Distribution plots are a potential means to discriminate between different generations of sand dunes for other dune fields as well, supporting the concept that the complex patterns observed in dune fields are composite features, the product of discrete punctuated events of dune construction.