What Controls Mafic Eruption Style? The Causes and Consequences of Coupled Vesiculation and Crystallization Kinetics in Ascending Basaltic Andesite Magmas

是什么控制了火山喷发的风格？上升玄武安山岩岩浆的耦合囊泡和结晶动力学的原因和后果。涉及基性岩浆的爆炸性喷发对活火山附近的危险具有重要意义。特别是，斯特龙堡火山喷发会产生大量细灰、高灰羽和大面积的扩散区域，可能会严重影响周围的人口。许多研究表明，爆炸性与上升减压岩浆排出的气体有关，这反过来又取决于岩浆的孔隙度-渗透性和破碎风格。为了阐明脱气过程及其对喷发样式的影响，本文建议对实验减压的基性硅酸盐熔体渗透率的发展进行实验研究，重点研究基性岩浆的结晶作用对喷发样式的控制作用。具体而言，同升微岩结晶如何影响连通囊泡网络的发育和渗流阈值，以及这些因素如何影响喷涌型管道和过渡中的气体分离？要测试的假设包括：[1]晶体数密度是否与减压速率（即，由于水合基性熔体在泡化过程中的快速结晶）直接相关？2)熔体渗透率是否与岩浆粘度成反比？3)减压驱动结晶是否改变了渗透阈值（即通过限制气泡膨胀或通过对气泡放置的空间控制）？4)减压速率是否通过控制脱气效率和同喷发结晶的深度和效率来影响基性喷发类型？这些问题将通过减压实验，在与阿拉斯加Okmok火山喷发的成分相似的合成玄武质安山岩熔体上，用纯水和混合H2O-CO2流体相来研究CO2对结晶和泡化动力学的影响。实验将与中全新世Okmok火山的自然样品进行比较，该火山产生了强烈的冲积期至次平期和火山喷发矿床。渗透仪?将用于测量实验样品和天然样品的渗透率，以估计渗透阈值，并将结果用于模拟爆炸性岩浆喷发期间的气体分离和破碎。更广泛的影响：该项目将支持UAF的博士研究生和本科生助理。将与UAF阿拉斯加本土科学与工程项目（ANSEP）建立新的联系，目的是雇用阿拉斯加本土本科生为该项目进行研究。该项目还将涉及与火山学家凯西·卡什曼（布里斯托尔大学）的国际合作。π吗?与阿拉斯加火山观测站的合作也有助于将这项研究应用于评估与阿拉斯加和卡斯卡迪亚活火山猛烈的岩浆喷发有关的火山危害。UAF实验岩石学实验室的新研究设备的开发也将增强UAF的基础设施，并提供新的设备，可以满足地质和火山学研究以外的研究需求，包括在其他物理科学和工程学科的应用。

What controls mafic eruption style? The causes and consequences of coupled vesiculation and crystallization kinetics in ascending basaltic andesite magmas. Explosive eruptions involving mafic magmas pose important implications for hazards near active volcanoes. In particular, Strombolian eruptions produce large volumes of fine ash, high ash plumes, and large dispersal areas that may severely impact surrounding populations. Numerous studies suggest that explosivity is related to expulsion of gases from ascending, decompressing magmas that in turn depends on porosity-permeability properties of the magma and fragmentation style. In an attempt to elucidate the degassing process and its effect on eruptive style, it is proposed to investigate experimentally the development of permeability in experimentally decompressed mafic silicate melts with particular focus on the role of crystallization in mafic magmas as a control on eruptive style. Specifically, how does syn-ascent microlite crystallization influence development of connected vesicle networks and the percolation threshold, and how do these factors influence gas separation in the conduit and transitions in eruptive style? Hypotheses to be tested include: [1] Are crystal number densities related directly to decompression rate (i.e., due to rapid crystallization of hydrous mafic melts during vesiculation)? 2) Is melt permeability inversely related to magma viscosity? 3) Does decompression­driven crystallization change the percolation threshold (i.e., by limiting bubble expansion or by spatial control on bubble placement)? 4) Does decompression rate affect the style of mafic eruptions by controlling degassing efficiency and the depth and efficiency of syn­eruptive crystallization? These questions will be investigated via decompression experiments on synthetic basaltic andesite melts similar in composition to those erupted at Okmok volcano (Alaska), and with both pure water and mixed H2O­CO2 fluid phase to examine the influence of CO2 on crystallization and vesiculation kinetics. The experiments will be compared with natural samples from the mid­Holocene Middle Scoria Okmok volcano, which produced violent strombolian to subplinian and vulcanian eruption deposits. A ?permeameter? will be constructed to measure permeabilities of both experimental and natural samples to estimate percolation thresholds, and the results will be used to model gas segregation and fragmentation during explosive mafic eruptions. Broader Impacts: This project will support a PhD student, and undergraduate student assistant at UAF. A new link will be forged with the UAF Alaska Native Science and Engineering Program (ANSEP) with the aim to hire Alaska Native undergraduate student(s) to perform research for the project. The project will also involve international collaboration with volcanologist Kathy Cashman (University of Bristol). The PI?s association with the Alaska Volcano Observatory also facilitates application of this research to assessment of volcanic hazards related to violent mafic eruptions at active volcanoes in Alaska and Cascadia. Development of new research equipment in the UAF Experimental Petrology lab will also enhance the infrastructure at UAF and provide new equipment that could fill research needs beyond geology and volcanology studies, including applications in other physical sciences and engineering disciplines.