Topographic forcing of dune distribution and local wind regime around simple domes and irregular structures in Olympia Undae, Mars

Introduction

Olympia Undae, in the north circumpolar region of Mars, is one of the largest dune fields on the planet and a key site for investigating the interaction between aeolian transport, sediment availability and local relief. Dune morphology in this region records both the regional circumpolar circulation and local perturbations caused by topographic obstacles [1,2]. In addition to its dune field, Olympia Undae contains non-impact landforms including Simple Domes (SD) and Irregular Structures (IS), which locally modify airflow and sediment redistribution [3–5] (Fig. 1). These edifices provide natural markers to analyse how topography controls dune distribution and inferred near-surface wind regime.

Data and methodology

This study focuses on the 6 Simple Domes and 5 Irregular Structures identified in Olympia Undae [3–5]. The analysis combines MOLA topography, HRSC/MOLA digital terrain models, orbital imagery, and GIS-based morphometric analysis using tools such as JMARS [3–5]. Dune distribution on and around each structure was compared with local altitude and slope in order to evaluate the topographic control on sediment accumulation and mobility.

The methodology is based on a structured analysis of elevation (h) and slope (S) derived from HRSC/MOLA DEM data, organised on a spatial grid (latitude–longitude) (Fig. 2), allowing the extraction of morphometric gradients and their relationship with dune occurrence.

Two diagnostic parameters are defined and applied: the critical altitude and the limiting slope. The critical altitude corresponds to the elevation above which dunes become scarce or absent and is computed from altitude gradients (dh/dx) using percentile thresholds (typically absent and identify significant topographic transitions associated with changes in wind behavior. The limiting slope represents the maximum terrain inclination allowing dune mobility and is derived from slope distributions using a similar percentile-based approach. This value is defined by identifying from which slope values of moving dunes surfaces are usually uncommon under normal conditions [5].

Both parameters are calibrated using dune distribution and morphology, including crest orientation and dune type, and their spatial relationship with HRSC/MOLA-derived elevation and slope data, allowing a direct link between topographic forcing and inferred wind regime.

Results

The results show that dune distribution around the SD and IS of Olympia Undae is markedly asymmetric and strongly controlled by local topography. As expected, dunes preferentially accumulate on low-slope flanks and sheltered sectors, whereas summit areas and more exposed sectors tend to be dune-free or to show reduced sediment cover. This confirms that the edifices locally modify near-surface airflow and sediment transport pathways [5].

IS-01 is one of the catalogued Irregular Structures shown in Fig. 1 [3,4]. With an overall relief of approximately 423 m, it clearly illustrates this pattern (Fig. 3). Above an altitude of –4727.8 m, the presence of dunes decreases sharply, defining a critical threshold. The same structure shows a limiting slope of about 1.021° [5]. However, summit slopes are below 1°, indicating that the lack of dunes cannot be explained by slope alone. Instead, this is interpreted as the effect of wind interaction and turbulence over the summit, which prevents sediment accumulation, whereas the flanks favour belts of linear dunes [5].

Other edifices confirm that the topographic effect is systematic, although expressed differently according to morphology. In IS-04, the calculated values are –4742.2 m for critical altitude and 1.485° for limiting slope [5]. Because of its irregular shape and internal slope variability, part of the structure remains covered by dunes. Its surface includes linear dunes aligned NW–SE, barchans in transition to barchanoids, and curved dune patterns that suggest local variations in wind intensity and direction superimposed on the dominant circumpolar flow [1,2,5] (Fig 4).

The SD also records this coupling between topography and wind. In SD-01, transverse dunes, barchanoids and barchans occur on different sectors of the edifice. The main inferred wind direction is NW–SE, in agreement with the regional circumpolar circulation, while a secondary NE–SW component is indicated by oblique crests in the eastern and southern sectors [1,2,5]. The relief appears to promote sectorial sediment trapping and differential erosion.

Summary and Conclusions

The simple domes and irregular structures of Olympia Undae act as local topographic obstacles capable of reorganising dune distribution and modifying the local expression of the regional wind regime. The combined use of critical altitude and limiting slope provides a useful framework to identify where dunes can form and where sediment transport is inhibited by wind–topography interaction [5].

The observed asymmetries in dune occurrence, the concentration of mobile dunes below critical thresholds, and the contrast between exposed summit areas and sediment-rich flanks indicate that local relief exerts a first-order control on aeolian redistribution at the scale of individual edifices. The results support the interpretation that dune patterns around the SD and IS of Olympia Undae can be used to infer local atmospheric circulation in the Martian polar environment [1,2,5].

References

[1] Ewing, R. C., Peyret, A. P. B., Kocurek, G., and Bourke, M.: Dune field pattern formation and recent transporting winds in the Olympia Undae dune field, north polar region of Mars, J. Geophys. Res. Planets, 115, E08005, 2010.

[2] Rubanenko, L., Gunn, A., Pérez-López, S., Fenton, L. K., Ewing, R. C., Soto, A., and Lapôtre, M. G. A.: Global surface winds and aeolian sediment pathways on Mars from the morphology of barchan dunes, Nat. Astron., 7, 1037–1047, 2023.

[3] Sánchez-Bayton, M., Herraiz, M., Martin, P., Sánchez-Cano, B., Tréguier, E., and Kereszturi, A.: Morphological analyses of small and medium size landforms in Scandia Cavi and Olympia Undae, Northern Circumpolar Region of Mars, Planet. Space Sci., 210, 105389, 2022.

[4] Sánchez-Bayton, M., Herraiz, M., Martin, P., Sánchez-Cano, B., Tréguier, E., and Kereszturi, A.: Morphometric and topographic data of small and medium size landforms in the Northern Circumpolar Region of Mars, Data in Brief, 43, 108417, 2022.

[5] Sánchez-Bayton Sánchez, M.: Zona Circumpolar Norte de Marte: Análisis Físico y Morfológico de Estructuras Pequeñas y Medianas en Scandia y Olympia Undae mediante Datos de Sensores Remotos de ESA Mars Express, Mars Global Surveyor y Mars Reconnaissance Orbiter, PhD thesis, Universidad Complutense de Madrid, Universidad Complutense de Madrid, 2025.