Estimating Eruption Model Input Parameters From Direct Observations of Deeply Eroded Basalt Conduits, San Rafael, UT

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”火山给全世界数百万人带来了危险，包括许多生活在美国部分地区的人。科学家们现在可以预测许多监测良好的火山喷发的时间。不幸的是，目前还不可能准确地预测一次喷发的爆炸性，因为这取决于很多因素，比如火山导管的形状和岩浆的组成，其中大部分取决于地下深处的活动过程，因此在喷发前无法直接观察到。更好的预测取决于我们对控制地下火山管道内岩浆流动的条件的理解。该项目旨在通过对犹他州南部圣拉斐尔沙漠中深度侵蚀的古火山的地质调查，提供关键数据，以提高这种认识。这种独特的地质环境，数百万年来没有火山爆发，为火山爆发期间地下的运作过程提供了重要的见解。我们不能直接观察目前正在喷发的火山的这些过程，但我们可以从地质记录中保存下来的特征来解释它们。Connor、Wetmore和同事们将把地质测绘与三维地面激光雷达成像、地球化学和岩石学建模以及对岩石弹性特性的分析结合起来，详细了解控制圣拉斐尔沙漠火山导管形成的侵蚀和混合过程。进行这些观测的基本目标是对管道流动和火山喷发模型中常见的一组输入参数施加地质和地球化学约束。这将通过以下方式实现：(1)利用地面激光雷达通过地质测绘生成单个火山导管的三维模型。这将使管道进入计算机，并允许项目团队测量横截面积、形状和半径随高度的变化，直接测量管道流动和发展的数值模型所需的管道几何形状。这种方法可以研究岩脉和管道之间的详细三维关系，角砾岩（寄主岩石-岩浆）混合带，以及其他足够详细的特征，对管道模型有用。(2)对从这些管道中系统收集的样品进行详细的结构和地球化学分析，将有助于了解管道两侧和沿线岩浆的矿物学和化学变化。这些数据将约束模型中使用的喷发参数，如岩浆温度、初始挥发性含量（从原生基性矿物的熔融包裹体中获得）、粘度、结晶深度和这些参数中的跨管道梯度。(3)对管道所在围岩的性质进行详细描述。这一描述将包括微观结构研究，旨在量化围岩的变形机制、应变类型和强度，以及与管道距离的函数。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Volcanoes create hazards for millions of people worldwide, including many living in parts of the USA. Scientists can now forecast the timing of many eruptions at well-monitored volcanoes. Unfortunately, it is currently not possible to accurately forecast how explosive an eruption might be, because this depends on a large number of factors, such as the shape of volcano conduits and the composition of magma, most of which depend on processes operating in the deep subsurface and so are not directly observable prior to eruptions. Better forecasts depend upon improving our understanding of the conditions that govern magma flow within volcanic conduits in the subsurface. This project aims to provide crucial data to improve this understanding through investigation of the geology of deeply eroded ancient volcanoes in the San Rafael desert of southern Utah. This unique geologic environment, where volcanoes have not erupted in millions of years, provides essential insight about processes operating in the subsurface during volcanic eruptions. We cannot observe these processes directly at currently erupting volcanoes, but we can interpret them from the features preserved in the geologic record. Connor, Wetmore and colleagues will combine geologic mapping with 3D terrestrial LiDAR imaging, geochemistry and petrological modeling, and analysis of the elastic properties of host rocks to develop a detailed understanding of the erosion and mixing processes that controlled formation of volcanic conduits of the San Rafael desert. The basic goal of making these observations is to place geological and geochemical constraints on a set of input parameters common to models of conduit flow and volcanic eruptions. This will be accomplished by: (1) generating 3D models of individual volcano conduits through geologic mapping utilizing terrestrial LiDAR. This will essentially bring conduits into the computer and allow the project team to measure cross-sectional areas, shapes, and change in radius with height, direct measures of conduit geometry needed in numerical models of conduit flow and development. This approach will allow study of the detailed 3D relationships between dikes and conduits, and breccia (host rock - magma) mixing zones, among other features in sufficient detail to be useful in conduit models. (2) Detailed textural and geochemical analyses of samples systematically collected from these conduits will yield insights into variations in mineralogy and chemistry of magmas across and along conduits. These data will constrain eruption parameters used in models, such as magma temperature, initial volatile content (obtained from melt inclusions in primary mafic minerals), viscosity, depth of crystallization, and across conduit gradients in these parameters. (3) The properties of the wall rock that hosts conduits will be carefully described. This description will include microstructural studies aimed at quantifying deformation mechanisms, strain type and intensity in the wall rocks, as a function of distance from the conduits.