Intellectual merit. Although it is commonly accepted that the behavior of volatile elements in magmas controls eruption dynamics, the depth and amount of vapor exsolved, as well as the distribution and transport of vapor bubbles in shallow magmatic systems remain poorly constrained. This project aims to develop a novel multidisciplinary methodology to quantify where and how much vapor degassing occurs, how fast vapor bubbles are transported in different magmatic environments, if they are expected to accumulate in the shallower portion of the system and how much effect this accumulation will have on eruption dynamics. A fundamental observation to be explained is the discrepancy between emitted volatiles released during explosive eruptions and the amount of volatiles that can be dissolved in the melt prior to eruption (excess degassing). The clearest example of excess degassing is associated with S mass balance, because S release during and after eruptions can be measured accurately by spectroscopic methods. Several open questions will be addressed: (1) How much vapor can be present in a magma prior to an eruption and what fraction was exsolved in-situ versus transported from deeper unerupted magma (ex-situ)? (2) If ex-situ degassing is important, what controls the accumulation of bubbles in the shallowest part of the magma body and how does it affect the eruptive behavior of the magma? The proposed work is transformative in that it will explore the poorly understood transport and storage of exsolved volatiles in magmatic systems with new numerical models developed by the PIs, and it will integrate geochemical data (trace elements in apatites and pyrrhotite) with thermodynamic modeling (expected vapor content as function of crystallinity) and fluid dynamics modeling into a novel approach to quantify the volatile budget in magmas. Existing thermodynamic models will be used that include H2O (e.g., MELTS) and H2O-CO2 (e.g., VolatileCalc) solubilities to determine, for a range of reasonable initial conditions, the percentage of exsolved vapor in given examples of Plinian eruptions with documented S excess (Mount St. Helens 1980, El Chichon 1982, Pinatubo 1991, Krakatau 1883, Katmai 1912, Taupo 181 AD) as well as for larger, older S-rich units (Kos Plateau Tuff 160 ky, and Fish Canyon Tuff 28 Ma) for which the S atmospheric load is poorly-constrained. In the same units, published data and/or analyses of apatites and pyrrhotites by electron microprobe will be used to determine (a) whether the magmas were vapor-saturated in their shallow reservoirs prior to eruption (using a geochemical test we have developed) and (b) using zoning profiles in apatites, how volatile element contents vary prior to eruption. Finally, multi-phase flow models will be developed using different numerical techniques to estimate how mobile vapor bubbles are across the magmatic system and how quickly they accumulate in reservoirs before an eruption. Such models will provide invaluable new insights in the dynamics of volcanic eruptions.
Broader impacts. This project will support a graduate student, and will train her/him in a highly multi- disciplinary and inherently quantitative environment, enabling him/her with those fundamental skills of modern science. It will provide a new investigator (Huber, no prior funding) funds to develop an active group in physical volcanology and will also allow two young faculty members to continue an active multi-disciplinary collaboration that has been successful over the last few years. Finally, the PIs propose to develop a short course for advanced undergraduate and graduate students on merging modeling techniques and geochemical analyses applied to magmatic processes. PI Huber has been teaching a version on this course, over the last two years, as a week-long series of lectures and practical exercises at the University of California, Berkeley, the University of Geneva (Switzerland), and at Rice University. On the basis of the enthusiastic response of the students to this class, we expect that organizing such a course at Georgia Tech and University of Washington is likely to attract many local students, and would strongly help our community to become more aware and proficient in quantitative methods in Earth Sciences.
