Topographic Analysis of the Flanks of Alba Mons Using MOLA DEMs

This research employs morphometric analyses within a broader investigation of the geologic evolution of the northernmost Tharsis volcano, Alba Mons, Mars. We are using imaging and topographic datasets to produce 1:1M-scale geologic maps that document geologic features of the volcano's summit region and western flank and assess the styles and sequences of volcanism. Fluvial dissection is evident from valley networks that primarily exist on the northern flank. Image data from THEMIS IR and CTX were used to map two main types of volcanic features: distinctive tabular lava flows that extend for long distances and the curvilinear segments of collapsed lava tubes. Lava tubes often occur along the crests of prominent volcanic ridges. These collapse features are frequently discontinuous, likely due to both variations in primary volcanic processes and obscuration by degradation and mantling of the surface. In THEMIS IR images, volcanic ridges exhibit a subtle brightness contrast caused by slightly higher thermal radiance on sun-facing slopes. This contrast appears to correlate spatially with the crests of volcanic ridges both with and without collapsed segments, suggesting that ridge crests delineate long lava flow pathways extending across the flanks of Alba Mons. Where collapse features are not visible, tracing low relief volcanic ridges in image data is difficult. We performed an analysis of topography to validate and extend photogeological mapping and quantitatively characterize volcanic ridges. We utilized the MOLA MEGDR DEM to calculate slope, shaded relief, and curvature statistics over local (1, 2 and 5 km) and regional (10, 25 and 50 km) baselines. Topographic signatures of volcanic ridges are easily observed in a combination of transparent hillshade and plan convexity image data. The trace of a volcanic ridge can be mapped from the lowest values of plan convexity, which essentially is the intersection of MOLA topography and an XY plane. Plan convexity does not provide a continuous vector due to noise and higher frequency variations in slope, preventing a purely automated extraction. By combining these data with hillshade calculations, the topography are enhanced and can be used to connect segments of lava tubes and trace extensive lava pathways across Alba Mons' flanks, including 15 systems of 600+ km in length.