Aeolian dune-field pattern boundary conditions

Abstract

Aeolian dune-field patterns reflect the complex external environment within which the pattern evolves. These external environmental controls are the boundary conditions on aeolian dune-field pattern formation. The influences of boundary conditions such as wind regime and sediment supply are well-known, however, boundary conditions represent a relatively unexplored area of dune-field pattern formation. Source-area geometry and areal limits are two newly recognized boundary conditions. Measurements of crest spacing and crest length from satellite images of dune-field patterns with point and line source-area geometries show an increase in spacing and crest length over distance, whereas spacing and crest length in plane-sourced patterns emerge equally across the dune field. The impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model. Model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area, and that dune fields that are five times longer in the direction of dune migration than in the crest-parallel direction can achieve the greatest spacing within a given area. Empirical measurements of spacing, defect density and dune-field area from ten different dune fields, ranging over four-orders of magnitude in size, show that spacing increases and defect density decreases as dune-field area increases. Because the formation of all dune fields involves a wind regime and sediment supply, there must be interplay of boundary conditions within the same dune field. At different stages of pattern development one boundary condition may dominate over others, and with changing climatic, eustatic or tectonic parameters, boundary conditions may change to modify an existing pattern. Recognizing boundary condition controls on aeolian dune-field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change.