Comparison of Effusive Volcanism at Olympus, Arsia, Pavonis, and Ascraeus Montes, Mars from Lava Flow Mapping Using Mars Express Hrsc

Introduction: The High Resolution Stereo Camera (HRSC) onboard ESA's Mars Express (MEX) orbiter [1] has provided 12.5 m/pixel projected images for a north-south transect of the four major Tharsis shield volcanoes. These data provide an unprecedented opportunity to examine lava flows at high resolution with regional context. Our objective is to characterize late-stage effusive processes and identify potential volcanic trends based on superposition relationships and types of lava flows similar to the approach used to characterize eruptive processes at Kilauea, Mauna Loa, and Mount Etna [2,3]. Our results provide new insight into the evolutionary stages of the Tharsis Montes originally defined by Crumpler and Aubele [4]. Background and Approach: Lava tubes and channels are structures that form during the emplacement of basaltic flow fields [5]. Although these features can transition between one another within a flow field, they generally represent different emplacement conditions [5,6]. Terrestrial observations of active flows show that tubes form during longer-lived, steady effusions of lower viscosity lava. In contrast, channels form during shorter-lived, fluctuating, higher rate effusions of higher viscosity lavas [3,7-13]. Mapping of terrestrial shield volcanoes shows different abundances of these flow structures [2,3]. Because they tend to form as a result of different eruptive conditions, the abundance of each lava flow type can be used to characterize the eruptive history of that volcano. The HRSC provides high resolution images over large areal extent, enabling consistent mapping of lava flows. Our goal is to determine the abundance of tube-fed, channel-fed, and other flow types, to assess trends associated with their location on the flank, and to identify potential evolution in effusive processes. We map lava tubes based on the presence of sinuous chains of collapse pits, or in their absence we infer tube presence based on features interpreted to have formed by inflation. We map lava channels when leveed linear flows are resolvable. These same features were used previously to suggest the presence of martian tubes and channels [14-17 and others]. The north-south transecting HRSC images define the mapping areas for each volcano. We drape these data over the MOLA 128 pix/deg grid to provide a topographic base. The image mapping is supplemented