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When barchan dunes move over craters

Paulo Vitor Ribeiro Plácido, Danilo da Silva Borges, Willian Righi Assis, Erick de Moraes Franklin

TL;DR

This study uses subaqueous experiments to illuminate how a barchan dune interacts with crater-like depressions, varying dune/crater size ratios and flow conditions to map outcomes. A two-parameter framework, namely the dune–crater size ratio $D/D_c$ and a modified Stokes number $St(2H_c/D_c)$, organizes five interaction regimes from trapping to overpassing with fragmentation, with a quantified interaction timescale relative to bedform turnover. The resulting $D/D_c$–$St(2H_c/D_c)$ map, built with machine-learning classification, provides a predictive reference for Martian dune–crater dynamics, albeit with caution due to differences in density ratio and saturation length between water and Martian aeolian/arlike environments. The work highlights crater-induced flow structures as key drivers of dune morphodynamics and offers a framework to interpret long-timescale dune transport in cratered terrains on Mars.

Abstract

We investigate the possible outcomes of a subaqueous barchan moving over a crater-like depression in the bed. For that, we carried out experiments where we varied the dune size, crater and grain diameters, and flow velocities. We found that subaqueous barchans can be blocked, destroyed, or pass over craters, with transitional situations, and that strong instabilities take place under some conditions. Based on a dune-crater size ratio and a modified Stokes number, we propose a map that classifies the different outcomes of interactions. If used with caution, the map can serve as a reference for understanding the much slower behavior of dunes migrating over or near craters on the surface of Mars.

When barchan dunes move over craters

TL;DR

This study uses subaqueous experiments to illuminate how a barchan dune interacts with crater-like depressions, varying dune/crater size ratios and flow conditions to map outcomes. A two-parameter framework, namely the dune–crater size ratio and a modified Stokes number , organizes five interaction regimes from trapping to overpassing with fragmentation, with a quantified interaction timescale relative to bedform turnover. The resulting – map, built with machine-learning classification, provides a predictive reference for Martian dune–crater dynamics, albeit with caution due to differences in density ratio and saturation length between water and Martian aeolian/arlike environments. The work highlights crater-induced flow structures as key drivers of dune morphodynamics and offers a framework to interpret long-timescale dune transport in cratered terrains on Mars.

Abstract

We investigate the possible outcomes of a subaqueous barchan moving over a crater-like depression in the bed. For that, we carried out experiments where we varied the dune size, crater and grain diameters, and flow velocities. We found that subaqueous barchans can be blocked, destroyed, or pass over craters, with transitional situations, and that strong instabilities take place under some conditions. Based on a dune-crater size ratio and a modified Stokes number, we propose a map that classifies the different outcomes of interactions. If used with caution, the map can serve as a reference for understanding the much slower behavior of dunes migrating over or near craters on the surface of Mars.

Paper Structure

This paper contains 5 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Materials and Methods
  3. Results and Discussion
  4. Extrapolation of subaqueous results to Martian dunes
  5. Conclusions

Figures (3)

  • Figure 1: (a)-(e) Snapshots placed side by side showing the time evolution for the Trapped, Trapped with mass loss, Flow-induced fragmentation, Overpassing with mass loss, and Overpassing cases, respectively. The crater rim is highlighted by a dashed line in the snapshots, and the flow is from left to right. (f)-(i) HiRISE image (High Resolution Imaging Science Experiment, https://www.uahirise.org/[Dataset], n.d.) showing examples of barchan dunes interacting with impact craters on the surface of Mars. Morphological patterns in these Martian examples exhibit striking similarities with the regimes shown in (a)-(e). The right side of Panel (i) is a zoom in the region marked (red square) on the left side, and shows a bedform trapped inside a crater. Coordinates: latitudes [71.8741°N, 10.573°N, 23.190°N, 12.884°N], longitudes [345.094°E, 357.246°E, 339.585°E, 356.280°E], spacecraft altitudes [276.0, 287.3, 287.3, 279.5 km]. Courtesy NASA/JPL-Caltech/UArizona.
  • Figure 2: Outcomes of interaction for large craters, $D/D_c$$\leq$ 0.16. (a)-(c) Snapshots stacked vertically showing the time evolution for the Trapped, Trapped with mass loss, and Flow-induced fragmentation, respectively. The crater rim is highlighted by a dashed line in the snapshots, and the flow is from left to right. (d) HiRISE image (High Resolution Imaging Science Experiment, https://www.uahirise.org/[Dataset], n.d.) showing examples of Martian dunes interacting with large craters on the surface of Mars (-41.407° latitude, 44.587°E longitude, spacecraft altitude 253.9 km). Courtesy NASA/JPL-Caltech/UArizona. Panel (e) is a zoom on a region of panel (d), Courtesy NASA/JPL-Caltech/UArizona
  • Figure 3: (a)Different outcomes classified in the $D/D_c$ vs. St$(2H_c/D_c)$ space (barchan to crater size ratio and modified Stokes number, respectively). The symbols are listed in the key and the lines separating the different regions were drawn using SVM (support vector machine) and k-nearest neighbors (KNN) for refinement. The hatched region corresponds to a transitional case between Trapped and Trapped with mass loss. (b) Characteristic time$t_{char}$ for completing an interaction with the crater, normalized by the turnover time $t_{turn}$, as a function of the $D/D_c$. The symbols are the same used in panel a. (c)-(g) Time evolution of the projected area $A_p$ upstream, inside, and downstream the crater, shown for the crater–barchan interaction regimes: (c) Trapped, (d) Trapped with mass loss, (e) Flow-induced fragmentation, (f) Overpassing with integrity loss, and (g) Overpassing. The area $A_p$ (horizontal projection) is normalized by the initial upstream area $A_{up}$.