Reconstructing Explosive Magma Vesiculation

重建爆炸岩浆囊泡

• 批准号: 1019872
• 负责人: Helge Gonnermann
• 金额: $ 23.17万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1019872&HistoricalAwards=false
• 关键词: Reconstructing; Explosive; Magma; Vesiculation

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.

1912年，阿拉斯加诺瓦普塔火山的普林尼亚人喷发是最大的历史爆炸爆发，也是这项研究的主题。 Plinian喷发具有很高的爆炸性强度和破坏性。它们可以持续数天，单个Plinian阶段持续数小时，并产生数十公里高的热气和火山颗粒。这些火山羽可以在半球形或全球范围内分散，具有重大的社会影响。产生Plinian喷发的关键机制是岩浆挥发物的“爆炸性”释放，例如水，二氧化碳和硫，以及将喷发岩浆爆发成碎屑的“爆炸性”碎片。后者是猝灭岩浆的大小颗粒，包括火山灰。岩浆挥发物的爆炸性释放与岩浆碎片化以导致plinian爆发的重点是该项目的重点。该项目将涉及1912年novarupta preutuption pycroclasts中测得的囊泡大小分布的数值建模。囊泡尺寸分布提供了岩浆上升条件的直接记录，可以通过对升降岩浆中的气泡成核和生长进行建模来研究，这都是在上升驱动的减压期间岩浆易变的结果。从中得出给定的火山细胞的上升岩浆的时刻历史是确定模型对观察到的囊泡尺寸分布的拟合的关键参数。这项研究将检验以下假设：在Plinian喷发期间，减压率令人惊讶，以及气泡成核和岩浆碎片如何相关的问题。显然，大量的减压速率才能将保留的大量气泡定为拟南芥，只能在很短的时间内持续，大概是在岩浆碎片片段之前或可能是在很短的时间内。据认为，碎裂是累积气泡过压的结果，超过了岩浆的拉伸强度。该项目将通过全面的定量分析将喷发产品的现有观察分析与有关气泡成核和岩浆碎片化的理论和经验工作整合在一起。正如有据可查的1912年记录在1912年的Novarupta Pyroclast样品所记录的那样，岩浆减压，气泡成核，气泡生长和最终的岩浆破碎的重建，预计将在我们对爆炸性火山爆炸性火山爆发尤其尤其是爆炸性火山爆发方面带来新的进步。