CAREER: The Effect of Bubbles on Magma Dynamics

点击翻译按钮获取中文摘要

Volcanoes have exerted a fascination since the dawn of civilization. Eruptions, besides their obvious associated hazards, are one of the rare expressions of the dynamics of the Earth over timescales that are easy to comprehend from our standpoint. Over the last decades, our community has recognized the importance of exsolved volatiles (gas bubbles) on the chemical and physical evolution of magmas in the shallow crust and on eruption dynamics. The complexity of volcanic processes and our inability to observe directly how magmas evolve prior and during volcanic eruptions has seriously limited our ability to predict the timing and behavior of volcanic eruptions. With this project, we propose the development of new numerical methods, complemented with fluid dynamics experiments to provide a quantitative understanding of how the exsolution of gases affects the physical properties of magmas, their chemistry (and the composition of gases released to the atmosphere) and ultimately how bubbles behave collectively and affect the behavior of magmas erupting at the Earth surface.Magmas are multiphase systems composed of a very viscous ambient fluid (silicate melt), crystals and sometimes complemented by exsolved (immiscible) gas bubbles. In order to predict how magmas evolve before and during eruptions, we need to develop dynamic models that allow us to accurately represent the interplay between these three phases under various conditions. In this project, we plan to study first the exsolution and growth of water-rich bubbles to model their effect on chemical differentiation, i.e. how secondary gas phases such as sulfur species and CO2 partition into growing bubbles. The amount of sulfur incorporated into bubbles before an eruption is significant to quantify the impact of eruptions on climate (sulfur is a potent aerosol that affects the radiative balance in the atmosphere). The chemistry of the exsolved gas phase and its participation in a future eruption depend on the efficiency of phase separation in magmas and the possible accumulation of gas bubbles in parts of the reservoir that are more likely to erupt (lower viscosity). Our second task is to study the physics of phase separation, bubble-crystals-melt, more specifically to understand how the magma motion is impeded or facilitated by the presence of discrete bubbles and crystals. Finally, once the rheology of multiphase magmas is better constrained, we plan to use these results and study how buoyant gas bubbles migrate in zoned magma reservoirs. The question we aim to answer is whether bubbles are prone to accumulate in regions of low or high crystal content and how this accumulation affects the chemistry of the gas in the bubbles and the eruptive behavior of the magma.The results of the proposed research will have broad implications for physical volcanology, petrology, geochemistry and fluid dynamics. It will provide quantitative constraints on the state of magmas stored in shallow crustal reservoirs and also provide a better account of the effect of bubbles on magmas as they ascend to the surface during eruptions. Predictive models for the exsolution of sulfur in magmatic systems can also provide clues as to the climate impact of pre-historical large explosive eruptions (e.g. Toba, Cerro Galan). The goal of the proposed research is to provide quantitative tools and constitutive relations that will be widely available to interpret existing datasets (geochemistry of magmas, rheological experiments on magmas) and transfer this new knowledge to models of magma dynamics. Additionally, the development of new numerical methods to study multiphase fluid dynamics will impact the Computational Fluid Dynamics community and other fields in science and engineering, where particle suspensions or bubble emulsions are important (e.g. effect of fluid dynamics on biology, food processing?)