The Morphology of Martian Pyroclastic Ramparts and Their Use in Determining Vent-Proximal Eruption Dynamics

High-resolution investigations of Late Amazonian volcanic landforms provide previously unrevealed insights into the dynamics of Martian volcanic eruptions. On Earth, the formation of vent-proximal accumulations of spatter deposits is attributed to low-intensity lava fountaining episodes representing eruptions on the very edge of explosive activity. Martian spatter deposits form small-scale volcanic landforms that are rarely reported, and thus the dynamics of Martian mafic explosive eruptions are still not fully constrained. We conducted high-resolution Context Camera-based mapping coupled with a stereo-pair-generated digital elevation model to reconstruct the eruptive history of a fissure system and its associated products south of Ascraeus Mons, Mars. The studied volcanic fissure clearly demonstrates both explosive and effusive deposits and, in addition, is spatially associated with a lava channel. For the first time, these observations allowed us to conduct a comparative analysis of vent-proximal volcanic products and reconstruct the late-stage eruption dynamics of a fissure system. We found that the spatial distribution of the pyroclastic (spatter) rampart along the fissure vent is heterogeneous and generated using dynamic eruption processes. Moreover, the lava channel fed from the fissure vent shows evidence of successive lava overspills whose emplacement was topographically controlled. These observations suggest that, in contrast to the general inference that Amazonian-age volcanism mainly involves effusive eruptions, explosive-origin landforms might have been overlooked. Therefore, we argue that high-resolution mapping of pyroclastic deposits may provide critical insights into understanding the dynamic nature of Martian fissure eruptions and explosive-associated volatile release during the last stages of eruptions.