Abstract
Topography fundamentally influences the distribution and morphology of aeolian landforms via the modification of surface wind flow and the creation of space for sediment deposition. This has been observed at both landform (individual topographic dune forms) and macro-landscape (sand sea) scales. Although previous studies have considered several aspects of the impact of topography on aeolian landforms, the patterns of landscape-scale aeolian sediment accumulation that emerge at the meso-scale, within topographically complex environments have received less consideration.To address this, we present an approach that combines information on the presence of surficial sand (via remote sensing) with the morphometric feature classification method, LandSerf. Using the Cady Mountains in the Mojave Desert as a case study, we explore the relationships between sand cover and topographic indices over length scales of 102–103 m. Field observations are then used to refine our understanding of these patterns.Aeolian deposits across the Cady Mountains are strongly controlled by the topography. Although sand cover is often continuous and highly variable in depth, four archetypal “accommodation space types” are identified from the morphometric analysis: Slopes, Plains, Valley-Fills, and Slope-Valley composite. Specific aeolian landforms within these accommodation spaces may manifest as sand ramps and climbing - falling dunes, particularly on mountain front Slopes, and as sand sheets on downwind Plains within the mountain block. In areas of high sediment supply these may also coalescence, as exemplified by the extensive and compositionally complex Slope-Valley composites in the northern Cady Mountains.In conjunction with field observations, we argue that topography, moderated by proximity to sediment supply, strongly influences the character of the aeolian sedimentary record. However, even within the relatively complex landscape studied here, 90% of the mapped sand accumulation is associated with the four identified accommodation space types. The implication is that areas of such complex topography are amenable to analysis within the scheme outlined and that this can potentially be used to support interpretations of accompanying dune chronologies.
Highlights
Topography is a fundamental control on the transportation and deposition of aeolian sediment across a range of spatial scales
This study considers how we achieve an understanding of such potentially complex scenarios, beginning with a more general question and aim: how can we characterise and understand the meso scale (102–103 m) patterns of aeolian sediment accumulation within landscapes of topographic complexity? To address this we sought to develop a novel approach that considers how the character of a variable and partly continuous distribution of aeolian sand can be related in a semi-quantitative manner to the underlying topography
This study is primarily concerned with the influence of the meso-scale mountain topography on patterns of aeolian sediment accumulation, which we anticipate to span length scales of the order 102 to 103 m
Summary
Topography is a fundamental control on the transportation and deposition of aeolian sediment across a range of spatial scales. At the macro-scale (tens to hundreds of kilometers), topography influences the distribution of sand seas Wilson, 1973), as well as dune fields that develop within aeolian sediment transport pathways steered by macro-scale landscape structures. Topography controls the distribution and form of individual landforms at the micro scale (metres to tens of metres), as obstacles and vegetation induce local wind deceleration, acceleration, deflection and blocking (Howard, 1985; Hesse, 2019). Falling dunes form on lee slopes of obstacles (Ellwein et al, 2015), while lee dunes develop downwind of gaps between obstacles (e.g. Xiao et al, 2015)
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