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

火山学的最终目标是了解和预测火山爆发。火山学家面临的一个主要挑战是弄清楚火山内部发生了什么，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，因为可以看到和测量模型火山内的流动，同时记录由流动引起的振动，这些振动相当于真实的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。火山爆发有各种各样的风格，从熔岩流从顶部倾泻而出，到大气泡破裂的短暂事件，到岩浆滴的连续喷泉，再到高度爆炸性的喷发，碎片在许多公里高的柱中向上移动。气体是火山爆发的主要推动力，工程师在实验室实验中观察到的气液流动模式框架解释了各种类型的火山爆发。然而，工程师们的工作一直受到工业流体的推动，这些流体的粘度比岩浆低得多（也就是说，液体更容易流动），他们在比火山管道小得多的管道中进行了实验。因此，很难将工程结果正确地应用于火山流。该项目将汇集火山学家和工程师，在与火山爆发有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模拟物，并将观察各种气体流速，管道尺寸和糖浆粘度的流型和气泡几何形状。这将有助于我们了解不同喷发类型的起源。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学。声音，主要是在频率低于我们可以听到的（次声），是由所有类型的火山活动产生的，被认为与气泡和气体流动有关。玄武岩火山产生一些最有趣的次声，因为气泡合并（聚结），气泡上升和气体与周围液体分离（分离）都很容易，因为玄武岩与其他类型的岩浆相比粘度较低。这意味着有可能从次声中找出玄武岩火山内部气体流动的重要信息。上述空气-糖浆流动实验产生的声音将用麦克风记录下来，这样我们就可以将流动模式和气泡特性与它们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工具来测量有多少气体通过火山移动。这一点很重要，因为气体驱动火山喷发，并在控制喷发方式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。系统地了解在火山进行的次声测量如何与排放的气体通量相关，将使这种监测技术的全部潜力得以实现。最后，我们将使用实验和理论工作的结果来解释在斯特龙博利和埃特纳火山在意大利玄武岩喷发产生的次声。例如，我们将评估小型火山爆发是由大的单个气泡破裂引起的，还是由气泡云破裂引起的。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。

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.