SURFACE FOLDING ON LAVA FLOWS: INFLUENCES OF FLOW RHEOLOGY AND PRE-EXISTING TOPOGRAPHY

Lava flows with folded surface morphologies are common on Earth and other planets, and reflect the flow rheology, pre-flow topography, and emplacement (including eruption rates and atmospheric) conditions. Prior work has primarily used simple analytic models to relate fold wavelengths to viscosity ratios of the crust and lava, and from that suggesting compositions, with some success. Our goal is to produce a computational fluid dynamics (CFD) model that incorporates all of the major physical processes in the lava flow surface fold generation to allow better inferences of flow properties and emplacement conditions from the flow morphology.

We use COMSOL Multiphysics to model lava flows with a deformable free surface, a depth-dependent viscosity, and with variable flow base topography. As was predicted by the analytic models, we find that that surface folds at multiple wavelengths are generated in our computational solutions with exponential (or similarly large) decreases of viscosity with depth. Interestingly, we also find that the addition of topographic variations at the flow base, velocity variations within the flow, or flow rate variations from the flow source all affect the resulting surface fold wavelengths, which is beyond the capabilities of the analytic models to incorporate.

Here, we will present additional computational results that incorporate cooling and temperature-dependent viscosities, instead of an imposed viscosity function. These illustrate the effects of both compositional and environmental conditions (subaerial, seafloor, Venusian, Lunar, and Martian) on cooling and fold wavelengths. We expect these results to improve the reliability of using lava flow fold morphologies for inferring flow properties and emplacement conditions.