A NEW FINITE-ELEMENT MODEL FOR SOLIDIFYING LAVAS

The propagation of lava in effusive eruptions that form lava domes and flows is a competition between lava effusion at the vent and cooling and solidification that eventually arrest lava flows. Most numerical simulations of lava flows end when the bulk of the lava flow cools and undergoes crystallization or transition of the melt to a glass. However, many natural flows first solidify a surface crust which can experience lava breakouts in which lava advance resumes at the front or margins of a flow by rupturing through the solidified crust. Lava flow breakouts present a hazard during eruption response, but accurate prediction of their timing and location is not yet possible in commonly used flow models.

We present a new Finite Element (FEM) model for cooling, free-surface viscous flows based on the GetFEM library. The model is implemented using a python interface that allows modeling in both 2D and 3D with the option for user-specified shape functions. Level sets are used to track the evolution of the free surface and a solidified boundary layer that conforms to the glass transition temperature isocontour. We track the stresses within the solidified layer to identify the potential location and timing of crust disruptions that could result in breakouts . We vary upstream fluxes to understand conditions that favor disruption of the crust at the scale of a flow front or pahoehoe toe. Our findings can inform flow-field scale models on how to account for breakouts and inflation in a physics-based (rather than stochastic or random) way.