Introduction: Since Mariner 9 first imaged fluvial channels on the surface of Mars thirty years ago, one of the continuing problems of its hydrologic history has been the apparent absence of small, first-order tributaries to the large outflow channels and the larger integrated channels of the highlands [1]. Drawing on terrestrial examples from the northeast Sahara, where Quaternary climate has cycled between a savannah and hyperarid environment, the Mars-analogous landscape has been used in the past to promote the efficiency of aeolian processes [2-4] and the fluvial processes of sapping and headwall erosion [5,6]. Following up on the work of Haynes [7] more recent work on the landscape of the Sahara has emphasized the role of climate change in sculpting surface features [8]. Although we have yet to determine whether climate change on Mars was monotonic or cyclic during the late Noachian/early Hesperian, the processes may have the same end product. Discussed here are the processes of tributary obscuration based on terrestrial examples of aeolian infilling, landscape lowering and stabilization by development of a lag surface, and planation due to sand sheet formation and bedrock erosion.
Introduction: Mars is host to a wide range of aeolian forms such as dunes, ripples, dust devils, dust storms, yardangs, and ventifacts. Large dune fields characterized by low albedos and large duneform sizes have been observed and occur mainly around the north polar cap and in the southern mid-latitudes. However, another morphologically and dimensionally distinct population of aeolian bedforms have also been noted. These are generally brighter than the surrounding terrain, are about an order of magnitude smaller than the large, dark dunes (LDDs) and have simple forms. These bedforms have been designated ‘Transverse Aeolian Ridges’, or ‘TARs’ [1]. We have conducted a survey of all high-resolution (~1-11 m/pixel) Mars Orbiter Camera (MOC) images (~10,000 images) in a pole-to-pole swath between 0 and 45° E longitude to identify and classify TARs. This work extends the preliminary survey of [2], and was conducted on the opposite site of the planet. The aims are to determine TAR distributions, orientations, morphologies and morphometries, possible sediment sources, and superposition relationships with LDDs. Approximate percentage of areal coverage of TARs in each MOC image was recorded, as well as classification according to [3] and associations with other features such as LDDs and slope streaks. Distributions and orientations: The geographic distribution of TARs is significantly non-random: in the northern hemisphere, TARs are most commonly found between 0 and 35° N, particularly in the Terra Meridiani region. 668 MOC images in the northern hemisphere contained at least 5% areal coverage of TARs (Fig. 1). In the southern hemisphere, TARs are found between 0 and 55° S. 1591 MOC images in the southern hemisphere had 5% or more areal coverage containing TARs (Fig. 2). TARs tend to be found on crater floors and in regions containing mesas and layered terrains; in short, anywhere where significant mass-wasting can occur. The geographical distribution of different classes of TARs is also non-random: there are a much higher proportion of TARs classified as ‘barchan-like’ in the Meridiani region than anywhere else in the study region. Orientations of TARs (when not influenced by local topography) are consistent over large areas (cf. Fig. 3), suggesting that the wind regimes which control the formation of TARs are also consistent over wide areas. Figure 1. Percent areal coverage of TARs in MOC images for northern hemisphere. White dots represent MOC images with <5% TARs. Green dots show proportional percentages greater than 5%.
Abstract Dune length scale airflow modeling provides new insights on eolian bedform response and complex near‐surface 3‐D wind patterns not previously resolved by mesoscale models. At a 1‐m surface resolution, Curiosity wind data are used to investigate the eolian environment of the Namib dune on Mars, providing improved seasonal constraints on grainfall, grainflow activity, and ripple migration. Based on satellite images, airflow patterns, and surface shear stress, enhanced eolian activity, and slipface advancement occurs during early springtime. Autumn and winter winds are also favorable to eolian activity, but minimal movement was detected in satellite images overlapping with wind data. During the summer, the migration of large stoss ripples on the Namib dune may augment sediment deposition on the slipface. These results provide a better understanding of the overall migration pattern of the Namib dune, which can be extrapolated to other dunes in the Bagnold Dune Field.
Methods traditionally used to estimate the relative height of surface features on Mars include: photoclinometry, shadow length and stereography. The MOLA data set enables a more accurate assessment of the surface topography of Mars. However, many small-scale aeolian bedforms remain below the sample resolution of the MOLA data set. In response to this a number of research teams have adopted and refined existing methods and applied them to high resolution (2-6 m/pixel) narrow angle MOC satellite images. Collectively, the methods provide data on a range of morphometric parameters (many not previously available for dunes on Mars). These include dune height, width, length, surface area, volume, longitudinal and cross profiles). This data will facilitate a more accurate analysis of aeolian bedforms on Mars. In this paper we undertake a comparative analysis of methods used to determine the height of aeolian dunes and ripples.
