Articles techniques et présentations

Flow of lava in underground lava tubes is an important mechanism in volcanic eruptions. Most direct measurements of active lava tube flows are typically impossible due to unstable and dangerous terrain, high temperatures (2140°F / 1170°C), and complex and spatially extended tube networks spanning many miles. Computational simulations thus play an important role in understanding flow and cooling processes.

Past simulations have used idealized (e.g. oval) tube geometries. Recent advances in 3D laser scanning (LIDAR) have yielded detailed measurements of several drained lava tube caves at Lava Beds National Monument in Idaho. Here we use that laser point cloud data to construct a CAD flow domain for a natural lava tube. This is imported into COMSOL Multiphysics^® simulation software for use as a 3D computational domain to study laminar and turbulent flow processes and cooling in the simulated tube.

We model the problem using the CFD Module and Heat Transfer Module of COMSOL Multiphysics^®. The rheology of the material is poorly constrained, so a range of laminar and Non-Newtonian models are used. The flow is gravity driven and, for initial runs, is assumed to be isothermal. We find COMSOL Multiphysics^® solutions for each of several rheologies, and find that the range of plausible rheologies yields regimes from laminar to turbulent flows.

Our initial results allow reconstruction of the range of possible flow rates within natural tubes, something previously unknown. The shear rate solutions and flow dynamics also provide insight into mechanisms for the evolution of tube shape. Preliminary results combining flow and cooling suggest that the flow dynamics and cooling are closely coupled through the temperature-dependent rheology. We anticipate adding the COMSOL Multiphysics^® Geomechanics Module in the future to assess lava cave mechanical stability, an area of great interest in planning for lunar and Martian exploration.

This work demonstrates the feasibility of modeling flow and cooling processes for lava without resorting to idealized geometry. The increasing availability of LIDAR topography (surface or cave) thus enables a new understanding of volcanic processes once thought too complex to model. The approach of imported detailed topography for construction of CAD models, and subsequent COMSOL Multiphysics^® modeling of flow and cooling processes, is expected to become instrumental in understanding volcanic flows on Earth and throughout the Solar System.