Morphology and distribution of common ‘sand’ dunes on Mars: Comparison with the Earth

Abstract

Massed crescentic ridges are the most common dunes in the north circumpolar erg and crater floor dune fields on Mars; they are similar in plan to dunes that are typical of many desert basin ergs and dune fields on Earth. This correspondence implies that the dynamics of dune formation are similar on the two planets, despite martian constraints on dune formation that include much higher velocity winds required to move 'sand' in saltation, the possible inhibition of sand movement by absorbed water vapor and the seasonal 'snow' cover in the north circumpolar erg, and a probably sparse sand supply. Scale ratios derived from measurements of martian dunes at latitude 72øN, longitude 53 ø and latitude 47.5øS, longitude 331 ø are almost identical to scale ratios for much smaller gypsum dunes at White Sands, New Mexico. Isolated, scattered barchan dunes probably show thinning of dune sediments toward the southern margin of the north circumpolar erg on Mars, indicating a diminished sand supply and/or deflation of parts of the region by high speed winds. A complex dune formed by the apparent collision of barchans on Mars suggests that dunes of different sizes there, as on Earth, migrate at different rates. The present activity of the martian dunes, however, is not known, and they may be at least seasonally inactive. Uniform dune patterns in areas of 'sand' accumulation on Mars, as on Earth, reflect the long-term adjustment of eolian bedforms to wind regimes, sand supply, and topographic variations. Boundary ridges of sand that delineate the margins of many topographically controlled dune fields and ergs on Earth also occur on Mars. Complex ak16 patterns on Mars, as on Earth, probably reflect locally complex wind regimes. Wind erosion grooves in some of the martian dunes, and the apparent superposition of some dunepatterns in the north circumpolar erg may record changes in the eolian regime there. Preservation of these features implies condsiderable cohesion of the dune sands. Large through-going longitudinal dune belts, common on Earth, are not seen on Mars. The absence of 'sand-passing' dunes of this type and the restriction of 'sand-trapping,' massive crescentic dunes to a few sites on Mars, suggest that much of the available sand has been removed from the martian plains. Mars may have a long eolian history in which much of the sand suitable for saltation has already been transported to the north polar erg and crater floor fields. On Earth the formation of 'mature' ergs is estimated to require 2 x 106 years or more. By analogy, the massive dunes on Mars probably required as much or more time to accumulate. The age of their formation is not known; it may extend to periods when climatic conditions were possibly more earthlike than at present. INTRODUCTION A concentric swirl of dunes forms a 'sand' sea (erg) of Saharan proportions around the north polar ice cap on Mars (Figure 1). Between latitude 75 ø and 80øN, the dunes occur over an area of abøUt 1 x 106 km 2, about the same as the total area of the active basin ergs of No...

Martian surface winds: Insensitivity to orbital changes and implications for aeolian processes

“…However, we regard this situation as unlikely. It has long been known that the vast majority of the large Martian dunes as seen in the Viking Orbiter and Mariner 9 images are transverse in form [Breed et al, 1979], indicating that the winds strong enough to initiate saltation and form dunes are almost without exception unidirectional [Wasson and Hyde, 1983]. This is supported by the GCM calculations of wind modality made by Lee and Thomas [ 1995].…”

Dark material in the polar layered deposits and dunes on Mars

“…The north polar layered deposits appear to be the source of at least some of the dark material that composes the north polar erg. Breed et al [1979] interpreted the distribution of dunes in the erg to be consistent with sediment sources in the layered terrain. The volume of the erg is much less than the estimated volume of material eroded from the layered deposits, further supporting the hypothesis that the dune material was derived from erosion of the layered deposits [Thomas, 1982; Blasius et al, 1982;Lancaster and Greeley, 1990].…”

Remote sensing and spatial analysis of aeolian sand dunes: A review and outlook

“…In this regard, RS has been invaluable for comparing the diversity of dune morphologies between the two planets (e.g., Breed et al, 1979b;Schatz et al, 2006;Bourke, 2010). However, recent advances in the spatial resolution of image data from Mars, mainly from the High Resolution Imaging Science Experiment (HiRISE), have prompted several important contributions inferring both past and contemporary processes.…”

“…These foundational dune classifications have been related to controlling variables such as sand supply, vegetation cover, and wind directional variability (Fryberger and Dean, 1979;Wasson and Hyde, 1983). At roughly the same time, extensive tracts of dunes were discovered on the surface of Mars during the Mariner and Viking missions (e.g., Cutts and Smith, 1973;Breed et al, 1979b;Tsoar et al, 1979). It was found that, curiously, most extra-terrestrial dunes have almost identical morphology to those on Earth.…”