Constraining Surface Velocity Estimations of Debris-Covered Glaciers in Eastern Hellas, Mars, with a New 3D SHARAD Radargram

Debris-covered glaciers (DCGs) are viscous flow features found in the middle latitudes of Mars that preserve ice accumulated during obliquity changes in the Amazonian. Previous studies have estimated the ice precipitation rates at the massifs—around which the DCGs formed—and the ice flow velocities required to form these deposits using the flow law proposed by Goldsby and Kohlstedt (2001). This modeling depends on the surface and basal slope, ice thickness, and rheology. Studies based on Shallow Radar (SHARAD, 15–25 MHz) 2D profiles have reconstructed the basal topography of DCGs. However, off-nadir surface reflectors (“clutter”) often create ambiguities in the interpretation of the basal interface, and portions of the DCGs cannot be imaged due to limitations in the geometry of the spacecraft ground tracks. Thanks to a new 3D SHARAD volume of Eastern Hellas (29°S-61°S, 94°E-114°E), which overcomes these limitations, we obtained new and detailed constraints of basal topography for the DCG complex at Euripus Mons (Figure 1: 45°S, 105°E), allowing us to calculate driving stresses and model ice flow velocities. Following previous modeling in the same region, we set the ice density to 921 kg/m³, ice grain size to 2 mm, and dust content to 1%. We set present-day ice temperature, adjusted for latitude and slope, to 199 K, 201 K, and 203 K, for poleward-, westward-, and equatorward-facing lobes, respectively. We obtained driving stresses ranging from 36 and 67 kPa, and ice flow velocities, along the centerlines of each lobe, ranging between 0.1 to 0.5 mm/yr (Figure 1). The difference in driving stresses and ice-flow velocities in lobes of the DCG complex suggests local heterogeneities that could be associated with ice accumulation, debris input, and local topography of each lobe. We estimated the minimum ice temperature that would be needed to detect surface flow of lobe 6 over a 20-year period, which is close to the operational lifetime of HiRISE (25 cm/px). With an ice temperature of 222 K, the surface flow would be detectable assuming a minimum detectability equal to one pixel. However, studies have demonstrated the potential of sub-pixel motion detection using precise orthorectification and registration. With a detectability threshold of one-third of a pixel (8 cm), the surface flow would be detectable at an ice temperature of 213 K.