The Variability of Transverse Aeolian Ridges in Troughs on Mars

Introduction: A precursory glance at MGS images of the surface of Mars show an abundance of aeolian transverse ridges [1]. These ridges are located in a variety of geological terrains. Zimbelman and Wi lson [2] have separated the small-scale aeolian features of Syrtis Major into six categories: ripples associated with obstacles, ripple bands, ripple fields, ripple patches, isolated ripple patches and ripples associated with dunes. This paper focuses on one of these categories, that of ripple bands which tend to accumulate within linear troughs. As the origin of these features is still being studied (i.e. ripples versus dunes), we refer to them simply as transverse aeolian ridges. These ridges lie perpendicular to the trough orientation and often cover the entire trough floor. On Earth, transverse aeolian ridges develop in wind environments which display the least directional variability [3]. On Mars, transverse aeolian ridges have variable forms, chord length and wavelength. An understanding of the controls on this variability may help our understanding of trough wind patterns, sediment supply and landform genesis. This paper presents the results of a preliminary investigation into the controls on ridge variability. In particular, we are interested in variations of ridge form, wavelength and length. To this end we present a preliminary classification of ridge form and initial results on ridge wavelength and length. Methodology: We have focused our efforts on the Phaethontis quadrant (Mars Chart 24). To date over 3,400 Mars Orbital Camera (MOC) images have been examined for candidate sites. From these, 14 images have been selected and data from 27 sample sites collected. These locations fall into three geological type sites: grabens, troughs and valleys. Data has been collected on the transverse ridges (form, chord length, wavelength, orientation) over a mean sample distance of 800 m. Additionally, data has been collected on the form and dimension of the trough (width, depth, sinuosity, junction angle, channel floor morphology and trough orientation to prevailing wind).