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Coevolving aerodynamic and impact ripples on Earth

Nature Geoscience volume 17, pages 66–72 (2024)Cite this article

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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.

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Fig. 1: Examples and classification of mesoscale bedforms for a wide range of environmental conditions.
Fig. 2: Multiple growth instabilities in ambient air wind tunnel measurements.
Fig. 3: Estimating the subscale saturation length under ambient air conditions.
Fig. 4: Model predictions for ambient air conditions.

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Data availability

Source data for all main and supplementary figures are provided with the paper. All data generated by this study are available in the Texas Data Repository at https://doi.org/10.18738/T8/XA2LNX. The post-processed data are summarized in the Supplementary Information file (Supplementary Tables 1–5). Source data are provided with this paper.

Code availability

The code that extracts ripples’ wavelength from the pictures is provided with the paper. The code that integrates the equations of the hydrodynamic bedform model can be made available upon request from the authors.

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Acknowledgements

This research was supported by the Israel Science Foundation (ISF) (number 1270/20) for I.K., by the German–Israeli Foundation for Scientific Research and Development (GIF) (number 155-301.10/2018) for I.K. and K.K., by the National Natural Science Foundation of China (numbers 12272344, 12350710176) for T.P. and by the Texas A&M Engineering Experiment Station for O.D. This work has been funded by Europlanet grant number 871149 (project number: 20-EPN-054) for S.S., K.R.R., J.P.M. and G.F. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme.

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Author notes

  1. These authors contributed equally: Hezi Yizhaq, Katharina Tholen.

Authors and Affiliations

  1. Department of Solar Energy and Environmental Physics, Ben-Gurion University of the Negev, Be’er Sheva, Israel

    Hezi Yizhaq

  2. Institute for Theoretical Physics, Leipzig University, Leipzig, Germany

    Katharina Tholen & Klaus Kroy

  3. Department of Environmental, Geoinformatics and Urban Planning Sciences, Ben-Gurion University of the Negev, Be’er Sheva, Israel

    Lior Saban, Nitzan Swet & Itzhak Katra

  4. Division of Earth and Climate Sciences, Duke University, Durham, NC, USA

    Conner Lester

  5. Istituto Nazionale di Astrofisica, Osservatorio di Capodimonte, Napoli, Italy

    Simone Silvestro & Gabriele Franzese

  6. Carl Sagan Center, SETI Institute, Mountain View, CA, USA

    Simone Silvestro

  7. Department of Geoscience, Aarhus University, Aarhus, Denmark

    Keld R. Rasmussen

  8. Institute for Physics and Astronomy, Aarhus University, Aarhus, Denmark

    Jonathan P. Merrison & Jens J. Iversen

  9. Institute of Port, Coastal and Offshore Engineering, Ocean College, Zhejiang University, Zhoushan, China

    Thomas Pähtz

  10. Donghai Laboratory, Zhoushan, China

    Thomas Pähtz

  11. Department of Ocean Engineering, Texas A&M University, College Station, TX, USA

    Orencio Durán

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  1. Hezi Yizhaq
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Contributions

I.K., H.Y., L.S. and N.S. designed and conducted the ambient air wind tunnel experiments; K.T. devised the theoretical approach; O.D. and K.T. performed the theoretical hydrodynamic bedform modelling; C.L. conducted the impact ripple simulations; T.P. conducted the grain-scale transport simulations; H.Y., I.K., S.S., K.R.R., J.P.M., J.J.I. and G.F. designed and conducted the low-pressure wind tunnel experiments; O.D. and K.T. analysed the data; K.T., K.K., T.P and O.D. wrote the paper. All authors discussed the results and implications and commented on the paper at all stages.

Corresponding authors

Correspondence to Thomas Pähtz, Orencio Durán or Itzhak Katra.

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Nature Geoscience thanks Mathieu Lapôtre, Clément Narteau and Nathalie Vriend for their contribution to the peer review of this work. Primary Handling Editor: Tamara Goldin, in collaboration with the Nature Geoscience team.

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Supplementary information

Supplementary Information

Supplementary Methods (sections 1 and 2), Figs. 1–10 and Tables 1–5.

Supplementary Video 1

Coevolution of impact and aerodynamic ripples in ambient air wind tunnel.

Supplementary Video 2

Time evolution of height profile in impact ripple simulation.

Supplementary Video 3

Grain-scale simulation of mature impact ripples.

Supplementary Code 1

Code to calculate ripples’ wavelengths from images.

Supplementary Code 2

Source data for supplementary figures.

Source data

Source Data Fig. 1

Statistical source data (plain text).

Source Data Fig. 2

Statistical source data (plain text).

Source Data Fig. 3

Statistical source data (plain text).

Source Data Fig. 4

Statistical source data (plain text).

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Yizhaq, H., Tholen, K., Saban, L. et al. Coevolving aerodynamic and impact ripples on Earth. Nat. Geosci. 17, 66–72 (2024). https://doi.org/10.1038/s41561-023-01348-3

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