INSIGHTS INTO MARTIAN VOLCANISM BY THE HRSC EXPERIMENT ON MARS EXPRESS

The HRSC (High Resolution Stereo Camera) experiment on the European Space Agency's Mars Express orbiter has completed almost 4 years of operations, imaging almost all of the Tharsis and Elysium volcanic fields, as well as most other volcanic regions on Mars. The unique color and stereo data provided by the HRSC has enabled new studies of the formation, evolution, and styles of martian volcanic constructs and processes. Studies have focused on individual edifices/processes, as well as global assessments. Radial valley networks on some volcanoes (Hecates, Ceraunius) appear to be related to magmatic heating and melting of snowpack. Mapping of lava flow morphologies on Olympus Mons and on the Tharsis Montes show an evolution from tube-fed to channel-fed flows, with implications for the nature of the magma source underlying Tharsis. Lava flows on Ascraeus Mons had yield strengths, effusion rates, and eruption durations consistent with Hawaiian volcanoes. Syria Planum was dominated by both swarms of small shields, and a single larger edifice as the source of long lava flows. Finally, the wide areal coverage at consistently high resolution of HRSC images has enabled a chronology of Martian volcanism to be determined using crater statistical methods. We find that Olympus Mons, the Tharsis Montes, and Hecates Tholus likely formed by 3.5 Ga, but have continued to have effusive eruptions throughout Martian history, with multiple caldera-forming eruptions between 100 Ma to 1 Ga. Evidence suggests that the most recent volcanic eruptions on Mars occurred on Olympus Mons, as recently as a few Ma. In contrast, the highland paterae surrounding the Hellas basin (e.g., Hadriaca & Tyrrhena Paterae) ceased major eruptions prior to 1 Ga. The low-viscosity lavas flooding Gusev crater (MER Spirit landing site) are 3.65 Ga, and postdate older sediments. Further studies are in progress.