ERUPTION STYLES OF SMALL MARTIAN SHIELD VOLCANOES ON SYRIA PLANUM, FROM MOLA, TES, AND THEMIS DATA

Syria Planum, near the center uplift of the Tharsis Bulge, is characterized by hundreds of small shield volcanoes and flows. It is the largest field of plains-style volcanic shields on Mars. A few attempts have been made to model and describe the volcanic origin and evolution of this region, but Mars Orbiter Laser Altimeter (MOLA), Thermal Emission Spectrometer (TES), and Thermal Emission Imaging System (THEMIS) analysis now allows for more quantitative approaches to observation and analysis. Recent studies in the Eastern Snake River Plains (ESRP) volcanic field allows us to extend the quantitative approach to comparing the terrestrial and martian shields. This study uses MOLA, TES, and THEMIS data to better understand the range of Syria shield and flow morphologies, associated eruption styles, and search for potential regional controls on those styles, with the terrestrial shields as a baseline comparison.

We use 256 pixel/degree (230 meter/pixel) gridded MOLA data to calculate volumes and areas of shields and flows, as well as to measure topographic profiles to determine volcano diameters, local flank slopes, heights, summit crater dimensions, and other parameters. MOLA topographic profiles show Syria Planum volcanoes to be very similar to terrestrial basaltic shields in the ESRP in terms of the presence of flow fields, fissures, coalescing shields, summit craters, radial flow patterns, and low shield flank slopes. We find that Syria volcanoes have flank slopes averaging ~ 0.7 degrees, with a range of 0.1 – 1.6 degrees, and basal diameters of 10 – 35 km. The Syria volcanoes do not show the full range of shield morphologies visible elsewhere on Mars such as steepened slopes at the summit and the presence of parasitic steep-sided cones. Results from this study suggest that the eruptive style of Syria volcanic shields is relatively non-explosive compared to other martian volcanic plains fields. On the lower flanks of Syria, where local slopes increase, we find a transition from shields to large lava flows, however, the lava flow volumes are similar to the shield volumes, suggesting that source volumes for eruption sequences are similar.