Gas-Melt Flow Regimes in Basaltic Volcanic Conduits and their Characteristic Acoustic Signals

玄武岩火山管道中的气体熔体流动状态及其特征声信号

• 批准号: NE/G016593/1
• 负责人: Alison Rust
• 金额: $ 38.76万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG016593%2F1
• 关键词: Gas; Melt; Flow; Regimes; Basaltic

The ultimate goals of volcanology are to understand and predict volcanic eruptions. A major challenge for volcanologists is to figure out what is happening inside volcanoes even though we can only watch and make measurements at the top. Laboratory experiments can bridge this gap because it is possible to see and measure flow within a model volcano at the same time as record vibrations caused by the flow that are equivalent to vibrations measured by real volcano monitoring. The proposed project takes this approach to study how gases escape from volcanoes, and how the abundance of gas and flow patterns inside the volcano can be assessed from acoustic signals (sounds) measured with microphones. Volcanic eruptions come in all sorts of styles from lava flows pouring out the top, to brief events from large bubbles bursting, to continuous fountains of drops of magma, to highly explosive eruptions with fragments traveling upwards in columns many kilometres high. Gases provide the main driving force for volcanic eruptions and the various types of eruptions have been explained using the framework of gas-liquid flow patterns observed in laboratory experiments by engineers. However, the work by engineers has been motivated by industrial flows with liquids that have a much lower viscosity than magma (that is, the liquids flow much more easily) and they have run experiments in tubes that are much smaller than conduits in volcanoes. So it is difficult to properly apply the engineering results to volcanic flows. This project will bring together volcanologists and engineers to run experiments at conditions relevant to volcanic eruptions. In particular, we will use air and syrup as analogues for volcanic gases and melt, and will observe flow patterns and bubble geometries for a variety gas flow rates, tube sizes and syrup viscosities. This will help us to understand the origins of the different eruption styles. The second phase of the project will investigate the physics of sound generation by gas motion and bubble bursting. Sounds, mostly at frequencies below what we can hear (infrasounds), are produced by all styles of volcanic activity and are thought to be related to gas bubbles and gas flow. Basaltic volcanoes produce some of the most interesting infrasounds because bubble merging (coalescence), bubble rise, and gas separation from the surrounding liquid (segregation) are all easy because basalt has a low viscosity compared to other types of magma. This means that there is potential to figure out important information on the gas flow inside basaltic volcanoes from infrasounds. The sounds produced by the air-syrup flow experiments described above will be recorded with microphones so that we can link flow patterns and bubble properties to the volume and pitch of the sounds they generate. An additional goal is to test if we can effectively use infrasound recordings as a tool to measure how much gas is moving through volcanoes. This is important because gases drive volcanic eruptions and play a key role in controlling eruption style and intensity. Infrasonic monitoring has huge potential because it is cheap and easy to use compared to other methods for measuring gas outputs from volcanoes. Systematic understanding of how infrasonic measurements made at volcanoes are related to the gas fluxes emitted will allow the full potential of this monitoring technique to be realized. Finally, we will use the results of the experiments and theoretical work to interpret infrasounds produced by basalt eruptions at Stromboli and Etna volcanoes in Italy. We will, for instance, evaluate whether small volcanic explosions result from the bursting of large individual bubbles or whether the explosions are the bursting of clouds of bubbles. We also anticipate gaining useful information from more subtle sounds or infrasounds that we don't already know about because the experiments will tell us what to look for in the volcanic acoustic data.

火山学的最终目标是了解和预测火山喷发。火山学家面临的一个主要挑战是弄清楚火山内部正在发生什么，尽管我们只能在顶部观察和测量。实验室实验可以弥补这一差距，因为可以在记录流动引起的振动的同时查看和测量模型火山内的流动，这些振动相当于真实火山监测所测量的振动。拟议的项目采用这种方法来研究气体如何从火山中逸出，以及如何通过麦克风测量的声学信号（声音）来评估火山内部的气体丰度和流动模式。火山喷发有各种类型，从顶部涌出的熔岩流，到大气泡破裂的短暂事件，到连续不断的岩浆喷泉，再到碎片以数公里高的柱状向上传播的高度爆炸性喷发。气体提供了火山喷发的主要驱动力，工程师在实验室实验中观察到的气液流动模式框架已经解释了各种类型的喷发。然而，工程师们的工作受到工业流动的推动，液体的粘度比岩浆低得多（即液体更容易流动），并且他们在比火山管道小得多的管道中进行了实验。因此很难将工程成果正确应用到火山流中。该项目将汇集火山学家和工程师，在与火山喷发相关的条件下进行实验。特别是，我们将使用空气和糖浆作为火山气体和熔体的类似物，并将观察各种气体流速、管道尺寸和糖浆粘度的流动模式和气泡几何形状。这将有助于我们了解不同喷发方式的起源。该项目的第二阶段将研究气体运动和气泡破裂产生声音的物理原理。各种类型的火山活动都会产生声音，其频率大多低于我们能听到的频率（次声），并且被认为与气泡和气流有关。玄武岩火山会产生一些最有趣的次声波，因为与其他类型的岩浆相比，玄武岩的粘度较低，气泡合并（聚结）、气泡上升以及气体与周围液体分离（分离）都很容易。这意味着有可能从次声中找出有关玄武岩火山内部气流的重要信息。上述空气糖浆流动实验产生的声音将用麦克风记录，以便我们可以将流动模式和气泡特性与其产生的声音的音量和音高联系起来。另一个目标是测试我们是否可以有效地使用次声记录作为测量通过火山的气体量的工具。这很重要，因为气体驱动火山喷发，并在控制喷发类型和强度方面发挥关键作用。次声监测具有巨大的潜力，因为与其他测量火山气体输出的方法相比，它便宜且易于使用。系统地了解火山次声测量与排放气体通量的关系，将使这种监测技术的全部潜力得以实现。最后，我们将利用实验和理论工作的结果来解释意大利斯特龙博利火山和埃特纳火山玄武岩喷发产生的次声波。例如，我们将评估小型火山爆炸是否是由大的单个气泡破裂引起的，或者爆炸是否是气泡云的破裂。我们还期望从我们还不知道的更微妙的声音或次声中获得有用的信息，因为实验将告诉我们在火山声学数据中寻找什么。

项目成果

Numerical modeling of oscillating Taylor bubbles

• DOI: 10.1080/19942060.2016.1224737
• 发表时间: 2016-01
• 期刊: Engineering Applications of Computational Fluid Mechanics
• 影响因子: 6.1
• 作者: S. Ambrose;D. Hargreaves;I. Lowndes

The existence and behaviour of large diameter Taylor bubbles

• DOI: 10.1016/j.ijmultiphaseflow.2014.04.006
• 发表时间: 2015-06
• 期刊: International Journal of Multiphase Flow
• 影响因子: 3.8
• 作者: C. Pringle;S. Ambrose;B. Azzopardi;A. Rust

Numerical modelling of the rise of Taylor bubbles through a change in pipe diameter

• DOI: 10.1016/j.compfluid.2017.01.023
• 发表时间: 2017-04-22
• 期刊: COMPUTERS & FLUIDS
• 影响因子: 2.8
• 作者: Ambrose, Stephen;Lowndes, Ian S.;Azzopardi, Barry
• 通讯作者: Azzopardi, Barry

Experimental constraints on the outgassing dynamics of basaltic magmas

玄武岩浆放气动力学的实验约束

• DOI: 10.1029/2011jb008392
• 发表时间: 2012
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Pioli L

The rise of Taylor bubbles in vertical pipes

泰勒气泡在垂直管道中的上升

• 发表时间: 2015
• 作者: Ambrose Stephen