Insights into Highland Patera Volcanism using Mars Express HRSC Data

We have used images obtained by the High Resolution Stereo Camera (HRSC) on the ESA Mars Express orbiter to assess geologic activity at two of Mars' highland volcanoes: Hadriaca Patera and Tyrrhena Patera. HRSC images cover wide swaths at consistent lighting conditions and resolutions, making them ideal resources for assessing surfaces ages using crater statistics. Additionally, multi-channel HRSC images are processed to produce Digital Terrain Models (DTMs) that are of greater spatial resolution than MOLA-derived DTMs, which are useful to assess regional and local topographic variations. Crater size-frequency analyses and cratering model age estimates show both Hadriaca and Tyrrhena Paterae have complex surfaces shaped by volcanic, fluvial, and eolian processes. These ancient shields were formed early in martian history, 3.7-4.0 Ga. At Hadriaca Patera, the earliest detectable caldera activity occurred at 3.5 Ga, followed by explosive volcanic and fluvial activity on the flanks at 3.3-3.4 Ga. Later caldera activity occurred at 2.2-2.5 Ga and again at 1.1-1.6 Ga. At Tyrrhena Patera, explosive volcanic activity and emplacement of pyroclastic deposits occurred 3.5-3.6 Ga, with later fluvial erosional activity at 1.9-2.0 Ga and again at 1.2-1.5 Ga. Slopes on Tyrrhena Patera are generally shallower (0.09-0.4 degrees) than those on Hadriaca Patera (up to 0.7 degrees). Hadriaca's north flank trends uphill, suggesting that Hadriaca Patera settled due to removal of material during formation of Dao Vallis. Further study is underway to use HRSC topographic data and computer modeling to better understand pyroclastic volcanism at these two volcanoes