Rapid Decompression of Bubble-Bearing Magma and Implications for Eruption Style and Explosive Potential: An Experimental Study With Analogue Fluids

物理火山学中最重要的未解决的问题之一是了解是什么控制着火山爆发的风格，特别是在喷发和爆发风格之间的转变。目前，这种转变被认为是由两个关键过程控制的：碎片化和脱气。 通过碎裂，岩浆被分解成离散的碎片。因此，含有熔体和气泡的粘稠岩浆转化为粘稠度低得多的气流，可以迅速爆炸性地喷发。脱气是指岩浆中溶解和出溶的挥发物的损失。由于喷发的驱动力往往由出溶气体的膨胀所控制，因此脱气应起到抑制爆发性喷发的作用。 该项目的主要目标是通过实验确定岩浆快速减压过程中碎裂和脱气之间的关系。实验将在一个由加州大学伯克利分校设计和制造的激波管装置中进行。将使用防腐剂流体以控制流体、气泡和气泡生长的性质。实验研究将允许确定1）预先存在的气泡，2）出溶，3）管道几何形状，和4）减压率的相对重要性的过程中，导致爆炸喷发。 实验结果将在理论模型的背景下进行解释，然后将实验室结果扩展到火山。这项工作最重要的长期影响将是为估计危险提供更好的物质基础。作为一个具体的例子，迄今为止获得的实验结果的一个含义是，岩浆的气泡含量是快速减压是否会导致爆炸性喷发的主要控制因素。因此，测定穹隆或地下岩浆体的泡囊性（使用某种远程方法）可以用来估计这些岩浆体造成的危害。 这个项目将提供一个研究生的培训机会，一个博士后，并为本科生介绍研究。外展将通过在加州大学伯克利分校，科学会议和参考出版物类的地方。预计该项目将导致工程和火山学社区之间新的跨学科合作。

One of the most important unresolved problems in physical volcanology is understanding what controls the style of volcanic eruptions, and in particular, the transition between effusive and explosive eruption styles. Currently, this transition is thought to be controlled by two key processes: fragmentation and degassing. Through fragmentation, magma is broken into discrete pieces. The viscous magma containing melt and bubbles is thus transformed into a much less viscous gas flow that can erupt rapidly and explosively. Degassing refers to the loss of dissolved and exsolved volatiles from the magma. Because the driving force of eruptions is often dominated by the expansion of exsolved gases, degassing should act to suppress explosive eruption. The main goal of the project is to determine experimentally the relationship between fragmentation and degassing during the rapid decompression of magmas. The experiments will be done in a shock tube apparatus, designed and built at the University of California, Berkeley. Analogue fluids will be used in order to control properties of the fluids, bubbles, and bubble growth. The experimental study will allow the determination of the relative importance of 1) preexisting bubbles, 2) exsolution, 3) conduit geometry, and 4) decompression rate on the processes that lead to explosive eruption. The experimental results will be interpreted in the context of theoretical models, which will then allow the scaling of laboratory results to volcanoes. The most important long-term impact of this work will be a better physical basis for estimating hazard. As a specific example, one implication of the experimental results obtained so far is that the bubble content of magmas is the primary control on whether rapid decompression will lead to explosive eruptions. Determining the vesicularity of domes or subsurface magma bodies (using some remote method) can thus be used to estimate the hazard posed by these magma bodies. This project will provide a training opportunity for a graduate student, a postdoc, and an introduction to research for undergraduates. Outreach will take place through classes at UC Berkeley, scientific conferences and refereed publications. It is expected that this project to lead to new interdisciplinary collaborations between the engineering and volcanology communities.