A methodology for constraining lava flow rheologies with MOLA

Topography as measured by the Mars Orbiter Laser Altimeter (MOLA), when supplemented with imaging data, can be used to infer physical emplacement processes in lava flows on Mars with a level of detail analogous to what can be done with unobserved lava flow eruptions on Earth. MOLA, Viking Orbiter and Mars Orbiter Camera (MOC) data are used to develop new inferences regarding the rheology of a typical lava flow near Elysium Mons on Mars. We present a technique that uses MOLA Precision Experiment Data Records (PEDRs) to directly determine the longitudinal thickness profile of lava flows. This technique is preferable to using gridded topography derived from MOLA, particularly for features such as lava flows, with thickness variations at the same scale as their surroundings. Thickness profiles and underlying slope estimates can then be compared with results from rheologic models. The longitudinal thickness profile of the Elysium example discussed here exhibits a concave-up flow surface that is consistent with an exponential viscosity increase. The viscosity shows a relative increase of about 50 times over the length of flow examined when the density of the lava increases as a result of lava degassing.