Collaborative Research: Waves in Volcanic Conduit-crack Systems and Very Long Period Seismicity at Kilauea Volcano, Hawaii

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An overarching goal of volcanology is to characterize eruptive activity and link this to the physical processes governing magma ascent and eruption, which are generally hidden from direct observation. This proposal will develop a modeling framework to image the inner workings of active volcanoes, such as at Kilauea, Hawaii, USA. Kilauea represents a unique natural laboratory: it exhibits frequent eruptions, a dense instrumental monitoring network to record these eruptions, and a long history of scientific study. Recent activity at the Halemaumau vent, from 2008 to the present day, is the primary observational target. Rock falls from the crater walls onto the active lava lake generate oscillations of the magma and gas within the conduit, explosions, and lake height variations, as evidenced through oscillatory ground motion recorded on the local sensor network. Models for this behavior must explicitly consider bubble growth, complex conduit geometry that includes branching cracks, and stratified, multiphase fluid flow to achieve consistency between seismic data, video of lake level fluctuations, chemical data that constrain gas contents, and textural data that constrain near-surface magma density and bubble content. Theoretical understandings of magma flow, gas solubility laws, and bubble growth gained as a result of this study should benefit the study of active volcanoes generally, as well as diverse applications arising in Earth science and industry that involve flow of bubbly fluids through networks of cracks. Both the modeling tools and results could ultimately be used to monitor active volcanoes, understand their dynamics, and inform eruption forecasts.This proposal describes a framework for the study of volcanic activity and interpretation of seismic observations at active, open vent volcanoes. The primary application is to short term (tens of minutes) unrest episodes at Kilauea volcano, Hawaii, associated with rock falls from the crater walls onto the active lava lake surface, which induce oscillations of the magma and gas within the conduit, explosions, and lake height variations, as evidenced through oscillatory ground motion recorded on nearby seismometers and tilt meters. These natural experiments provide a unique test for unsteady conduit flow models, which depend critically on knowing conduit geometry and fluid properties of magma (rheology, multiphase character, volatile content, solubility law), all of which are generally hidden from direct observation. The project team will develop a numerical modeling framework for multiphase flow, at much shorter timescales than typically studied, with seismic wave propagation through bubbly magma in conduits that include branching dikes and sills at depth, as is expected at many volcanoes. Pressure changes in the conduit-crack system cause elastic deformations of the conduit and crack walls. Coupling to the solid Earth enables prediction of seismic signals associated with waves and resonant oscillations of the magmatic system. Buoyancy, compressibility, viscous drag, and non-equilibrium bubble growth and resorption ? all of which vary with depth ? must be accounted for to predict mode properties. Branching dikes/sills at depth partially control mode periods and ground displacement. Observable periods and decay rates of seismic signals are thus linked directly to the evolving depth distribution of gas, conduit architecture, and viscous drag. Inversion of these signals will provide new constraints on the shallow magmatic system and total volatile content at Kilauea, and a new framework for probing unsteady eruptive processes.