Collaborative Proposal: Ash Particles and the Bubbles that Make Them: Measuring Bubble Size from Ash Fragments for New Insights Regarding Eruption Dynamics

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。火山爆发是由岩浆中的气泡快速增长驱动的，这些气泡在喷发柱中迅速膨胀。通过测量这些气泡破裂前的大小，就有可能探索危险的爆炸性喷发的过程。然而，要对喷发柱的内部进行所需的详细监测是不可能的，而且当最终的火山灰产物被观察到时，驱动喷发的气泡已经破裂了。因此，有必要检查单个灰烬颗粒的表面，以分析这些爆炸气泡在灰烬表面留下的印记。该项目旨在开发一种技术来确定这些气泡的大小分布，从而阐明爆炸过程中破碎之前的泡化和破坏过程。气泡的大小可以根据火山灰颗粒表面凹坑的曲率半径来测量。这些火山灰颗粒可能是在岩浆泡沫破裂之前存在的气泡间膜和高原边界的残余物，因此应该保留有关将它们分开的气泡的信息。气泡碎片曲率可以使用立体扫描电子显微镜（SSEM）衍生的单个火山灰碎片的数字高程图来构建。3D形状和气泡体积可以从气泡“陨石坑”的正交横截面上的印记曲率重建。这样，就有可能确定气泡的大小，即使膨胀的气泡在喷发过程中破裂（破碎）。本项目开发的技术将应用于最近爆发的富埃戈火山、斯珀尔火山和圣海伦火山的自然灰烬，并将量化气泡大小分布（BSD）、气泡数密度（BND）和灰烬粒径分布（PSD）之间的关系。这将有可能检验一些科学假设，这些假设可以确定高能火山喷发的岩浆泡化动力学与其产物之间的关系。预计这项研究将产生新的火山产物分析工具，供更广泛的火山学家社区使用，除其他外，应用于高能火山喷发的灰烬的预破碎泡沫化；过去和未来火山喷发的危害评估；以及平流层火山灰及其对气候的影响。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Explosive volcanic eruptions are driven by the rapid growth of gas bubbles in magma that burst in the eruption column as they rapidly expand. By measuring the size of these bubbles just before they burst, it is possible to explore the processes that culminate in dangerous, explosive eruptions. However, it is impossible to monitor the interior of an exploding eruption column at the level of detail required, and by the time the final volcanic product of ash is observable, the bubbles that drove the eruption have already burst. Consequently, it is necessary to examine the surfaces of individual ash particles to analyze the imprints that these exploding bubbles have left on ash surfaces. This project is directed to developing a technique to determine the size distribution of these bubbles, and thus shed light on the processes of vesiculation and disruption immediately prior to fragmentation during explosion. Bubble sizes can be measured on the basis of the radius of curvature of concavities on the surfaces of ash particles. These ash particles would have been the remnants of inter-bubble films and Plateau borders that existed prior to the fragmentation of the erupting magmatic foam, so should preserve information about the bubbles that separated them. Bubble fragment curvature can be constructed using digital elevation maps for individual ash fragments derived from Stereo-Scanning Electron Microscopy (SSEM). 3D shapes and bubble volumes can then be reconstructed from the imprinted curvatures in orthogonal cross sections of bubble "craters." This way, it is possible to determine bubble size, even when the expanding bubbles have burst during eruption (fragmentation). The technique developed in this project will be applied to natural ashes from recent eruptions of Fuego, Mt. Spurr, and Mt. St. Helens volcanoes, and the relations between bubble size distributions (BSD), bubble number densities (BND), and ash particle size distributions (PSD) will be quantified. This will make it possible to test a number of scientific hypotheses that can determine the relations between magma vesiculation dynamics of energetic volcanic eruptions and their products. It is expected that this study will result in new volcanic product analysis tools available for the broader community of volcanologists for application to, among others, pre-fragmentation vesiculation in ashes from highly energetic volcanic eruptions; hazard assessment of past and future eruptions; and stratospheric ash and its climate implications.