Mapping Fluvial Valleys on the Flanks of Alba Mons: Implications for Amazonian Watershed Development in Northern Tharsis, Mars

Abstract

This study characterizes fluvial activity on Alba Mons using a combination of image and topographic data to inform photogeologic interpretation and hydrological modeling. We produced a comprehensive digital inventory of fluvial valleys that documents the extensive dendritic and parallel drainage patterns dissecting Early Amazonian volcanic materials. Drainage density was correlated with regional slopes. On the summit and southern flanks, valleys are sparse and regional slopes are less steep, between 0.0° and 0.3° (average 0.4° ± 0.2°). Areas with higher drainage density (average 0.24 km⁻¹; locally >0.5 km⁻¹) have steeper regional slopes, between 0.1° and 2.9° (average 1.0° ± 0.4°). Ridged lava tubes and tabular lava flows represent local topographic highs that exert a strong influence on drainage patterns, but are also locally eroded by fluvial valleys. Graben formation and ice-rich mantle deposition complicate analyses by altering fluvial features. For two case studies, we employed an integrated approach that combined mapping and hydrological modeling to create watershed reconstructions that allowed robust morphometric analyses of drainage basins and the contained valley networks. Mapping shows well-preserved drainage patterns with morphometry and hypsometry that support a prolonged history of erosion and development into mature drainage networks. Modeling provides characterization of the downstream parts of drainage basins that are largely obscured. These results have climate implications, suggesting fluvial dissection resulted from widespread precipitation with possible contributions from meltwater related to periodic accumulation of ice-rich surface deposits.