Rheology of Lava Flows on Elysium Mons, Mars

Introduction: It is known from previous studies that in principle, the dimensions of lava flows reflect rheologic properties such as yield strength, effusion rates and viscosity [1-17]. In a previous study, we reported on such derived rheologic properties of lava flows on Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are located on the extensive Tharsis bulge [1,2]. Here, we expand on our previous study of lava flows on the Tharsis Montes by calculating the rheology of lava flows on Elysium Mons in order to investigate possible similarities and differences among the lava flows of the two major volcanic provinces located in two hemispheres on Mars. Data: We used images obtained by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft in combination with Mars Reconnaissance Orbiter Context Imager (CTX) images and Mars Orbiter Laser Altimeter (MOLA) data to identify, map, and measure the dimensions and slopes of lava flows in order to constrain their rheologic properties. We utilized several HRSC orbits with spatial resolutions of about 12.5-25 m/pixel and CTX images with 5-6 m/pixel spatial resolutions in order to measure the length and width of the studied lava flows. The heights and slopes of the lava flows were measured in individual MOLA profiles. Method: As in our previous studies, we make a few basic assumptions: (1) flow dimensions are related to the rheological properties of the flow, (2) rheological properties can be estimated from flow dimensions measured in remotely sensed data, (3) lava flows behave as Bingham fluids, (4) lava flows in laminar fashion, (5) no inflation of lava flows has occurred, (6) the densities of Martian volcanic rocks are on average 2,500 kg m, (7) the Graetz number is 300, and (8) the thermal diffusivity is on the order of ~10-10 ms with an assumed value of 3 x 10 ms. Moore et al. [4] and others [e.g., 5] related the yield strength ! of lava flows (Pa) to the flow dimensions by the following equations