SMALL VOLCANIC VENTS AS POTENTIAL EXPRESSIONS OF REGIONAL VARIATIONS IN LATE-STAGE MAGMATIC SUPPLY FOR THE THARSIS MONS

Recent Mars missions have returned topographic and image data that reveal many more small volcanic vents that are spread out over a significantly larger portion of the planet than previously thought. The high resolution image and topography coverage now allow not only better mapping of distribution, abundance, etc…, but comparisons between regions and within regions. Most of the martian small shield-building vents are on very shallow slopes (0.001-0.1 degrees), with channel and tube flows predominating on the steeper slopes. However, a noticeable exception is the set of small shields on the upper flanks of the Tharsis Mons volcanoes Arsia Mons (9°S 240°E), Pavonis Mons (0°N, 247°E), and Ascraeus Mons (11°N, 256°E), where the underlying slopes are an order of magnitude steeper (0.01-1 degrees). This study uses Mars Orbiter Laser Altimeter gridded and profile topography, and Mars Orbiter Camera and Thermal Emisssion Imaging Spectrometer visible and infrared images to measure typical parameters of small shield building vents for the three Tharsis Mons including: area, volume, profile, local slope, flank slope, elevation and diameter. We also record several less typical parameters such as asymmetry, alignment deviations from the maximum downhill gradient, volcanic productivity (volume/average flank slope) and representative flow widths. We compare the Tharsis Mons small shields to other martian and terrestrial small shield populations described in prior studies in order to consider possible effects of both magmatic plumbing differences and ambient (elevation, pressure, volatiles) conditions. As an additional constraint on possible local causes of variatibility among the Tharsis Mons upper flanks, we also use lava tube flow and channel flow observations and flow models from prior studies to compare estimated lava flow rates/viscosities.