Reconstructing Explosive Magma Vesiculation

1912年阿拉斯加诺瓦鲁普塔火山的普林尼式喷发是历史上最大的爆炸性喷发之一，也是本研究的主题。普林尼火山爆发具有很高的爆炸强度和破坏性。它们可以持续数天，其中普林尼阶段持续数小时，并产生数十公里高，持续的热气体和火山颗粒柱。这些火山羽流可以在半球或全球范围内扩散，产生重大的社会影响。产生普林尼式喷发的关键机制是岩浆挥发物的“爆炸性”释放，如水、二氧化碳和硫，以及喷发岩浆的“爆炸性”碎裂成火山碎屑。后者是淬火后的岩浆，包括火山灰，大小不一的颗粒。本项目的重点是岩浆挥发物的爆炸性释放和导致普林尼式喷发的岩浆破碎之间的相互关系，该项目将涉及对1912年诺瓦鲁普塔火山喷发的火山碎屑中测量的泡囊尺寸分布进行数值模拟。囊泡的大小分布提供了一个直接记录的岩浆上升的条件，可以通过建模的气泡成核和增长的上升岩浆，无论是上升驱动的减压过程中的岩浆挥发性出溶的后果进行调查。一个上升的包裹体的岩浆，从一个给定的火山碎屑的时间-压力的历史，是确定模拟观测到的泡大小分布的拟合的关键参数。这项调查将测试的假设，减压率是惊人的大普林尼火山爆发期间，以及如何气泡成核和岩浆破碎的问题是相关的。大的减压率显然需要成核的大量气泡保存在火山碎屑中的囊泡，只能持续很短的时间，大概是在岩浆破碎之前或期间。据认为，碎裂是积累的气泡超压超过岩浆的拉伸强度的结果。该项目将通过全面的定量分析，将现有的对喷发产物的观测分析与关于气泡成核和岩浆碎裂的理论和经验工作结合起来。由此产生的重建岩浆减压，气泡成核，气泡生长，并最终岩浆破碎，记录良好的1912年Novarupta火山碎屑样品，预计将导致新的进展，我们的理解一般的爆发性火山活动和普林尼风格的火山爆发，特别是。

The 1912 Plinian eruption of Novarupta volcano, Alaska is one the largest historical explosive eruptions and the subject of this study. Plinian eruptions are of very high explosive intensity and destructiveness. They can last for days with individual Plinian phases lasting for hours and producing tens of kilometers tall, sustained columns of hot gases and volcanic particles. These volcanic plumes can become dispersed on a hemispherical or global scale with significant societal impact. Key mechanisms to producing a Plinian eruption are the 'explosive' release of magmatic volatiles, such as water, carbon dioxide and sulfur, in conjunction with the 'explosive' fragmentation of the erupting magma into pyroclasts. The latter are variably sized particles of quenched magma, including volcanic ash. The interrelation between this explosive release of magmatic volatiles and magma fragmentation to result in a Plinian eruption is the focus of this project.This project will involve the numerical modeling of vesicle size distributions measured in pycroclasts from the 1912 Novarupta eruption. Vesicle size distributions provide a direct record of magma ascent conditions that can be investigated through modeling of bubble nucleation and growth in the ascending magma, both a consequence of volatile exsolution from the magma during ascent-driven decompression. The time-pressure history of an ascending parcel of magma, from which a given pyroclast is derived, is the key parameter determining the fit of modeled to observed vesicle size distributions. This investigation will test the hypothesis that decompression rates are surprisingly large during Plinian eruptions, as well as the question of how bubble nucleation and magma fragmentation are related. The large decompression rates apparently required to nucleate the large numbers of bubbles preserved as vesicles in pyroclasts can only be sustained for very short times, presumably immediately prior to or perhaps during magma fragmentation. It is thought that fragmentation is the consequence of accumulated bubble overpressure in excess of the magma's tensile strength. This project will integrate existing observational analyses of eruptive products with theoretical and empirical work on bubble nucleation and magma fragmentation through a comprehensive quantitative analysis. The resultant reconstruction of magma decompression, bubble nucleation, bubble growth and ultimately magma fragmentation, as recorded by the well-documented 1912 Novarupta pyroclast samples, is expected to lead to new advances in our understanding of explosive volcanism in general and Plinian style volcanic eruptions in particular.