FIELD AND LABORATORY MEASUREMENTS OF MULTI-PHASE LAVA RHEOLOGY

Lava and magma are complex multi-phase fluids comprised of liquid silicate melt, solid crystals, and gas bubbles. The physical properties of lava and lava flow emplacement and dynamics depend on the interactions between these phases. Yet our understanding of the behavior of multi-phase fluids is still incomplete.

We address this challenge by assessing the rheology of flowing lava in the field and lava analogs in the laboratory. Our field study uses a large (> 200) collection of aerial videos recorded during the 2018 Kīlauea Lower East Rift Zone eruption in Hawaii. We extract velocity fields of the lava surface using particle image velocimetry (PIV) and track the average and maximum velocities. Using a simple analytical expression (Jeffreys equation) we estimate the effective viscosity of the lava in each video. Thanks to the extensive coverage of the flow channel in both time and space, this dataset yields a profile of viscosity as a function of distance, in which we identify a linear increase in viscosity with distance up to 10 km from the vent. We then take a closer look at the details of the surface flow fields at several sites and invert for the lava’s rheology using a finite-element numerical model. This analysis reveals a slightly shear-thickening behavior.

In the lab, we explore the impact of bubbles and particles on the behavior and rheology of flows in a rectangular channel. Silicone oil and corn syrup serve as the liquid phase, plastic particles or sesame seeds as the solid phase, and gas bubbles are either N2 or CO2. We use the advance rate of flows with different particle and bubble contents to construct empirical constitutive relations for three-phase suspensions. We observe shear-thickening behavior in laboratory experiments with similar capillary numbers as those relevant to the Kīlauea lava flows. Using nuclear magnetic resonance imaging (MRI), we document phase segregation and localization in the interior of multi-phase flows. Together, these studies advance our understanding of multi-phase lavas, and, by extension, magmas and other fluids. We note that the research in this presentation was initially motivated by a dinner conversation with Kathy Cashman.