Geodetically modeled reservoir volume changes during volcanic eruptions are commonly much smaller than the observed eruptive volumes. This discrepancy is thought to be partially due to the compressibility of magma, which is largely controlled by the presence of exsolved volatiles. The 2006 eruption of Augustine Volcano, Alaska, produced an eruptive volume that was ∼3 times larger than the geodetically estimated syn-eruptive subsurface volume change. In this study, we use a multistep methodology that combines constraints from geodetic, volcanic gas, geologic, and petrologic data together with equations relating physical processes to observable parameters. We apply a Monte Carlo approach to quantify uncertainties. Ultimately, we solve for the exsolved volatile volume fraction and the magma compressibility. We estimate Augustine's 2006 pre-eruptive exsolved volatile phase to be ∼5.5 vol% of the magma at storage depths, yielding a bulk magma compressibility of ∼3.8 × 10⁻¹⁰ Pa⁻¹. We develop a novel approach to estimate the H₂O/CO₂ ratio of the syn-eruptive gas emissions in the absence of direct H₂O emission measurements which are hard to obtain due to the high background levels in ambient air. We find a best-fit H₂O/CO₂ molar ratio of 29. We also investigate the effects of applying different equations of state to our model. We find that the Ideal Gas Law might be used as a first approximation due to its simplicity; however, it overestimates volatile density and compressibility significantly at storage depths. This project capitalizes on the insights that can be gained by integrating multidisciplinary data with models of physical processes.

中文翻译：

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2006 年阿拉斯加奥古斯丁喷发的岩浆压缩性、喷发前溶出挥发分和 H2O/CO2 摩尔比的多学科约束

火山喷发期间大地建模的储层体积变化通常比观察到的喷发体积小得多。这种差异被认为部分是由于岩浆的可压缩性，这在很大程度上受外溶挥发物的存在控制。2006 年阿拉斯加州奥古斯丁火山的喷发产生的喷发量比大地测量估计的同步喷发地下体积变化大约 3 倍。在这项研究中，我们使用了一种多步骤方法，该方法将大地测量、火山气体、地质和岩石数据的约束与将物理过程与可观察参数相关联的方程相结合。我们应用蒙特卡罗方法来量化不确定性。最终，我们求解出溶出的挥发分体积分数和岩浆压缩率。我们估计奥古斯丁^-10 帕^-1。我们开发了一种新的方法来估计协同喷发气体排放的 H ₂ O/CO ₂比率，因为没有直接的 H ₂ O 排放测量，由于环境空气中的背景水平高而难以获得。我们找到了最合适的 H ₂ O/CO ₂摩尔比为 29。我们还研究了将不同状态方程应用于我们的模型的影响。我们发现理想气体定律由于其简单性可以用作第一近似值；然而，它在储存深度显着高估了挥发物密度和可压缩性。该项目利用了通过将多学科数据与物理过程模型相结合而获得的见解。