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

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。爆炸性火山喷发是由岩浆中气泡的快速增长推动的，当它们迅速膨胀时，这些气泡在喷发柱中破裂。通过测量这些气泡在破裂前的大小，就有可能探索最终导致危险的爆炸性喷发的过程。然而，要以所需的细节水平监测正在爆炸的喷发柱的内部是不可能的，当火山灰的最终火山产物可见时，驱动喷发的气泡已经破裂。因此，有必要检查单个火山灰颗粒的表面，以分析这些爆炸的气泡在火山灰表面留下的印记。该项目旨在开发一种技术，以确定这些气泡的大小分布，从而阐明爆炸过程中紧接在破碎之前的泡化和破裂过程。气泡的大小可以根据火山灰颗粒表面凹陷的曲率半径来测量。这些火山灰颗粒可能是喷发的岩浆泡沫碎裂之前存在的气泡间薄膜和高原边界的残留物，因此应该保存了将它们分开的气泡的信息。气泡碎片曲率可以使用来自立体扫描电子显微镜(SSEM)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“凹坑”的垂直横截面上的压印曲率重建出来。这样，即使膨胀的气泡在喷发(碎裂)过程中破裂，也可以确定气泡的大小。该项目开发的技术将应用于最近福戈山喷发的天然灰烬。Spur和Mt.将量化气泡大小分布(BSD)、气泡数密度(BND)和火山灰颗粒大小分布(PSD)之间的关系。这将使检验一些科学假说成为可能，这些假说可以确定高能火山喷发的岩浆气泡动力学及其产物之间的关系。预计这项研究将产生新的火山产物分析工具，供广大火山学家使用，除其他外，可应用于高能量火山喷发产生的灰烬中的碎裂前泡沫化；过去和未来喷发的危险评估；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.