Mapping the Four‐Dimensional Viscosity Field of an Experimental Lava Flow

Abstract

AbstractViscosity is a critical rheological property that determines the behavior, evolution, and final morphology of lava flows. Determining the viscosity of an active lava flow, however, is nontrivial. The rheological structure of lava is complex, and during active flow conditions, viscosity can change by orders of magnitude through space and time. This makes viscosity one of the most elusive properties of flowing lava. After almost a century of research on lava viscosity, it is still common practice to reduce the viscosity of a flow to a single value, generalizing an immense field of deviations and complexities. Considering lava viscosity as a one‐dimensional variable may be sufficient for characterizing some aspects of flows, but it does not allow for solving higher‐order rheological problems, such as depth structure, spatial variability, or rates of change. This study presents, for the first time, the four‐dimensional viscosity field of an actively flowing experimental lava. Results from this experiment include time‐series thickness, surface velocity, and temperature maps that are used to solve for the 4‐D viscosity of the lava flow with a spatial resolution of 2 cm. Additionally, the approach used in this study allows for an analysis of vertical rheological structure, specifically, crust and core viscosity layers. Although this study was performed in an experimental setting with crystal‐ and bubble‐free lava, the basic data collection techniques applied are common in field volcanology and thus could be applicable in certain natural settings.