Abstract:We present experimental results on the formation of streamwise asymmetric, migrating bedforms resulting from the transition of successive surface solitary waves (SSW) interacting with an initially flat sandy bottom. We analyze seven cases, with differing ratios between SSW height and water depth. For each experiment, we generated 400 SSWs having the same features, investigating their effects on the bed, in terms of near‐bed velocity and erosional patterns. Our work proves that SSWs can generate asymmetric bedf… Show more
“…2 a). In contrast, aspect-ratio scaling for barchanoid and transverse dunes generally follows observed patterns for subaqueous dunes 24 , 25 . Fig.…”
Wherever a loose bed of sand is subject to sufficiently strong winds, aeolian dunes form at predictable wavelengths and growth rates. As dunes mature and coarsen, however, their growth trajectories become more idiosyncratic; nonlinear effects, sediment supply, wind variability and geologic constraints become increasingly relevant, resulting in complex and history-dependent dune amalgamations. Here we examine a fundamental question: do aeolian dunes stop growing and, if so, what determines their ultimate size? Earth’s major sand seas are populated by giant sand dunes, evolved over tens of thousands of years. We perform a global analysis of the topography of these giant dunes, and their associated atmospheric forcings and geologic constraints, and we perform numerical experiments to gain insight on temporal evolution of dune growth. We find no evidence of a previously proposed limit to dune size by atmospheric boundary layer height. Rather, our findings indicate that dunes may grow indefinitely in principle; but growth depends on morphology, slows with increasing size, and may ultimately be limited by sand supply.
“…2 a). In contrast, aspect-ratio scaling for barchanoid and transverse dunes generally follows observed patterns for subaqueous dunes 24 , 25 . Fig.…”
Wherever a loose bed of sand is subject to sufficiently strong winds, aeolian dunes form at predictable wavelengths and growth rates. As dunes mature and coarsen, however, their growth trajectories become more idiosyncratic; nonlinear effects, sediment supply, wind variability and geologic constraints become increasingly relevant, resulting in complex and history-dependent dune amalgamations. Here we examine a fundamental question: do aeolian dunes stop growing and, if so, what determines their ultimate size? Earth’s major sand seas are populated by giant sand dunes, evolved over tens of thousands of years. We perform a global analysis of the topography of these giant dunes, and their associated atmospheric forcings and geologic constraints, and we perform numerical experiments to gain insight on temporal evolution of dune growth. We find no evidence of a previously proposed limit to dune size by atmospheric boundary layer height. Rather, our findings indicate that dunes may grow indefinitely in principle; but growth depends on morphology, slows with increasing size, and may ultimately be limited by sand supply.
Wherever a loose bed of sand is subject to sufficiently strong winds, aeolian dunes form at wavelengths and growth rates that are well predicted by linear stability theory 1-3 . As dunes mature and coarsen, however, their growth trajectories become more idiosyncratic; nonlinear effects 1 , sediment supply 4 , wind variability 5 and geologic constraints 6, 7 become increasingly relevant, resulting in complex and history-dependent dune amalgamations. Here we examine a fundamental question: do aeolian dunes stop growing and, if so, what determines their ultimate size? Earth's major sand seas are populated by giant sand dunes, evolved over tens of thousands of years 8,9 . We perform a global analysis of the topography of these giant dunes, and their associated atmospheric forcings and geologic constraints, and we perform numerical experiments to gain insight on temporal evolution of dune growth. We find no evidence of a previously proposed limit to dune size by atmospheric boundary layer height 10 . Rather, our findings indicate that dunes may grow indefinitely in principle; but growth slows with increasing size, and may ultimately be limited by sand supply. We also demonstrate that giant dune size depends on both wind climate and sand supply through their control on dune morphology, revealing a topographic signature of geologic and climatic forcing in Earth's sand seas.
“…Sea surface manifestations of internal waves can be detected, indeed, from Synthetic Aperture Radar (SAR) images (Alpers, 1985): they appear as brighter and darker alternate strips on the image, whether the surface waves associated to ISWs propagate in convergent or divergent surface flow zones (see Figure 1b). Evidence of ISWs is also inferred from their ability in reshaping the seafloor, giving rise to migrating bedforms (Droghei et al., 2016; La Forgia et al., 2019), and sediment resuspension (La Forgia, Tokyay, et al., 2020; Martorelli et al., 2021).…”
Internal solitary waves (ISWs) consist of hump-shaped large undulations of the pycnocline with a permanent form, resulting from a balance between nonlinearity, which tends to steepen it, and dispersion, which tends to flatten it (Grimshaw et al., 2010; Helfrich & Melville, 2006; Sutherland et al., 2013). ISWs are mostly generated by the interaction between tidal flows and bottom topographic features, such as underwater sills and the continental shelf-slope region (Helfrich & Melville, 2006; Osborne & Burch, 1980). Packets of shoreward-propagating ISWs, separated by tidal periods, are a ubiquitous feature of the coastal oceans (Dwi
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