Complementary classifications of aeolian dunes based on morphology, dynamics, and fluid mechanics

Abstract

Dunes form where winds blow over a bed of mobile sediment grains – conditions that are common in our solar system. On Earth, dunes abound in arid continental interiors and along sandy coastlines. Dune fields have also been recognized on other planetary bodies, including Venus, Mars, Saturn’s moon Titan, and Pluto. Despite the relatively basic conditions required for their formation, dunes adopt a rich diversity of shapes, sizes, and behaviors in response to their boundary conditions and other environmental forcings. Thus, people around the globe and over centuries have developed a rich vocabulary to describe dunes and their complexity. In addition, many studies have been devoted to link dune shape to environmental forcings, usually by means of correlations. As a result, existing dune nomenclature often includes redundant terms with differing definitions across scientific communities. Although a worthy first step, correlation-based classifications can be misleading if not based on an underlying mechanics and if dune morphogenetic classes are not uniquely defined. Here, we synthesize existing dune terminology and put the last two decades of research on dune morphodynamics in perspective in proposing three simplified dune classification schemes based on the state-of-the-art understanding of dune morphology, morphogenetic processes and coupling between sand bed, fluid flow and sediment transport. Together, these classifications provide a unified framework for geomorphologists, sedimentologists, geographers, physicists, and others to describe windblown sand dunes on Earth and beyond through their shape, dynamics, and size as a response to winds and boundary conditions.