Coevolving aerodynamic and impact ripples on Earth

Hezi Yizhaq, Katharina Tholen, Lior Saban, Nitzan Swet, Conner Lester, Simone Silvestro, Keld R. Rasmussen, Jonathan P. Merrison, Jens J. Iversen, Gabriele Franzese, Klaus Kroy, Thomas Pähtz, Orencio Durán, Itzhak Katra

Research output: Contribution to journalArticlepeer-review

Abstract

Wind-blown sand creates multiscale bedforms on Earth, Mars and other planetary bodies. According to conventional wisdom, decametre-scale dunes and decimetre-scale ripples emerge via distinct mechanisms on Earth: a hydrodynamic instability related to a phase shift between the turbulent flow and the topography and a granular instability related to a synchronization of hopping grains with the topography. Here we report the reproducible creation of coevolving centimetre- and decimetre-scale ripples on fine-grained monodisperse sand beds in ambient air and low-pressure wind tunnels, revealing two adjacent mesoscale growth instabilities. Their morphological traits and our quantitative grain-scale numerical simulations authenticate the smaller structures as impact ripples but point at a hydrodynamic origin for the larger ones. This suggests that the aeolian transport layer would have to partially respond to the topography on a scale comparable to the average hop length, hence faster than previously thought, but consistent with the phase lag of the inferred aeolian sand flux relative to the wind. A corresponding hydrodynamic modelling supports the existence of aerodynamic ripples on Earth, connecting them to megaripples and to the debated Martian ripples. We thereby open a unified perspective for mesoscale granular bedforms found across the Solar System.

Original languageEnglish
Pages (from-to)66-72
Number of pages7
JournalNature Geoscience
Volume17
Issue number1
DOIs
StatePublished - 1 Jan 2024

ASJC Scopus subject areas

  • General Earth and Planetary Sciences

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