Magma Waves, magma wagging and volcanic oscillations

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Volcanoes are dynamic and display a wide range of activity even before they erupt. Many volcanoes, especially the most destructive ones, undergo long slow oscillations in ground swelling, gas emissions and seismic activity, with periods between repeated peak activity of hours to days. Volcanoes may also experience tremor or shaking with much shorter periods of around one second. Such oscillations, with both day- and second-long periods, can last for weeks before an eruption occurs, and thus serve as important precursors to volcanic disasters. Understanding the cause for these oscillations is therefore critical for forecasting these disasters as well as for advancing the science of how volcanoes work. This project seeks to unify two leading physical models for both the slow ultra-long, i.e., day-long, period oscillations and volcanic tremor, with second-long oscillation periods. Our model explains long-period oscillations in terms of slowly ascending magma waves of gas pulses in the magma-filled volcanic conduit, which arrive sequentially at the surface, causing ground swelling and other activity such as small earthquakes. The shorter-period tremors are explained by a magma wagging mechanism in which the heavy column of magma in the volcanic conduit wags side-to-side inside of a spongy jacket of extra-bubbly magma. However, very-long and shorter period oscillations are not independent of each other; for example, long period oscillations involve cycles of enhanced volcanic tremor activity. The main goal of this project is to develop a 3-D (three-dimensional) model of bubbly magma in a volcanic conduit to account for the full range of oscillatory behavior, from rapid tremor to ultra-slow cycles. The central hypothesis of this study is that the evolution of magma waves in 3-D influences the onset of magma-wagging motion; this potentially provides a prediction for how long-period oscillations evolve and trigger (and sustain) shorter-period volcanic tremor prior to an eruption. The project also involves development of fundamental theories of two-phase physics that will, in addition to its impact on volcanic hazards, may contribute to better understanding of other problems of geological, environmental and energy-related processes.The models of magma waves and magma wagging are built from the same physics of two-phase systems,; the processes these models describe are inevitably coupled and influence each other's behavior. For example, degassing activity during long period cycles correlates with tremor, and our models suggest that gas emissions help drive tremor activity. Moreover, the current magma-wave model accounts for only vertical motion in one dimension, while the present magma-wagging model treats only horizontal movement in one-dimension. However, new preliminary models already suggest that the magma wagging entails circular swirling motion that can be detected from seismic stations. Magma waves are also likely to develop three-dimensional shapes, like spherical pockets near the center of the volcanic conduit, or stretched out bands near the conduit wall; these wave shapes would then affect how the magma column wags side to side. Accordingly, the primary activity of this proposal is to (1) develop the 3-D two-phase analytic theories of magma waves and magma wagging, including new physics such as gas exsolution and variable viscosity; (2) develop a 3-D unified numerical model of fully coupled magma wave and wagging evolution and activity; and (3) test the model predictions against new laboratory experiments, as well as existing seismological, ground-motion and gas-flux data, including recent observations from a pilot project in a volcano in Mexico. The goal of this work is to provide physical understanding and, ideally, model forecasting with a unified theory for the cause and evolution of long and short period oscillations, leading up to explosive volcanic eruptions. The magma wave and magma wagging models form the essential building blocks for a complete model of long and shorter period oscillations prior to volcanic eruption. The extension of these models into three-dimensions with more sophisticated physics, and their eventual unification into a single numerical model, will provide a wealth of predictions to further test the model with lab experiments as well as existing and new data. The model will provide insight into the dynamics and evolution of the volcanic magma column prior to an eruption, as well as a potentially important prognostic tool for volcanic hazards.