What lies beneath: feeding a basaltic volcanic eruption.

玄武岩火山爆发的类型很广，从相对温和的熔岩流出，到产生漂浮的火山灰柱的剧烈爆炸。喷发风格及其在时间和空间上的演变在很大程度上取决于岩浆在次火山管道系统中流动时发生的多相流体动力学过程。大多数玄武岩喷发都是由岩脉支撑的，岩脉是受侵蚀的玄武岩火山普遍存在的特征。当堤坝与地表相交时，它首先形成一个裂缝喷发。通常，火山爆发在几天内局限于一个火山口，并根据其活力形成火山锥或火山盾。在火山口下方，管道保持着堤坝的几何形状，各种证据表明，复杂的岩浆流动模式在堤坝内发育。了解岩脉内部的岩浆流动模式，以及它如何随时间变化，是至关重要的，因为它控制着地表喷发的性质。特别是，富气岩浆被定位为快速上涌的喷流，预计将促进更多的爆炸性喷发样式。这个项目的主要目标是：1。收集现场证据，利用实验室实验和/或数值模型，根据岩脉的结构证据重建火山导管中的岩浆流动过程；来解释英国和特内里费岛暴露的火山管道中的岩浆流动模式。气泡和晶体在岩脉中非常常见，并且常常表现出岩浆流动所施加的优先排列。这些结构提供了火山喷发过程中水流历史的记录，然而，由于缺乏对形成它们的过程的理解，对它们的解释受到了阻碍。在这个项目中，我们将根据申请人的技能，使用实验室实验和/或数值模拟，研究和量化含晶体和含气泡岩浆沿管道流动时的边际增加过程。结果将用于分析和解释在次火山管道系统中不同深度暴露的岩脉的现场样本，使我们第一次能够通过时间和空间重建岩脉流动过程。实验：熔融蜡中的气泡和颗粒悬浮物将被泵送通过一个有一个冷却壁的模型堤（高纵横比管道）。蜡会在壁上凝固，产生边缘沉积相，使用x射线计算机断层扫描对其进行结构分析。实验参数将系统地变化，包括：颗粒的大小、形状和浓度；气泡的大小和浓度；蜡流率；冷却速率;管道几何。参数将按自然系统比例调整。野外工作：在英国第三纪火成岩省的岩脉中暴露的纹理将在野外以晶体/囊泡尺度绘制，并收集样品进行XRCT和SEM分析。样品将告知实验室实验参数。随后在特内里费岛Teno地块的实地工作将侧重于绘制岩浆流动纹理指标的时空变化图，以重建四维流动模式。

Basaltic volcanic eruptions span a wide spectrum of styles, from relatively gentle effusion of lava, to violent explosions that produce lofting ash plumes. The eruption style, and its evolution in time and space, depends to a large extent on multiphase fluid dynamic processes that occur within the magma as it travels through the sub-volcanic plumbing system. Most basaltic eruptions are fed by dykes, which are a ubiquitous feature of eroded basaltic volcanoes. When a dyke intersects the surface, it first forms a fissure eruption. Usually, the eruption localizes to a single vent within a few days, and often builds a scoria cone or shield, depending on its vigour.Beneath the vent, the conduit retains a dyke geometry, and various lines of evidence indicate that complex magma flow patterns develop within the dyke. Understanding the magma flow pattern within a dyke, and how it changes with time, is crucial because it controls the nature of the eruption at the surface. In particular, localization of gas-rich magma into rapidly upwelling jets is expected to promote more explosive eruption styles.The main goals of this project are:1. to collect field evidence and use laboratory experiments and/or numerical models to reconstruct magma flow processes in volcanic conduits from textural evidence in dykes;2. to interpret magma flow patterns in exposed volcanic conduits in the UK and Tenerife.Bubbles and crystals are very common in dykes, and often show preferential alignment that is imposed by the magma flow. These textures provide a record of the flow history through an eruption, however, their interpretation has been hindered by a lack of understanding of the processes that create them. In this project we will investigate and quantify the process of marginal accretion of crystal- and bubble-bearing magma as it flows along a conduit, using laboratory experiments and/or numerical modelling, depending on the skills of the applicant. Results will be used to analyse and interpret field samples from dykes exposed at different depths within the subvolcanic plumbing system, allowing us, for the first time, to reconstruct dyke flow processes through time and space.Experiments:Suspensions of bubbles and particles in molten wax will be pumped through a model dyke (a high-aspect-ratio duct) with one cooled wall. The wax will solidify against the wall, producing a marginally-accreted facies that will be texturally analysed using x-ray computed tomography. Experimental parameters will be systematically varied, including: size, shape and concentration of particles; size and concentration of bubbles; wax flow rate; cooling rate; duct geometry. Parameters will be scaled to the natural system.Fieldwork:Textures exposed in dykes of the British Tertiary Igneous Province will be mapped at the crystal/vesicle scale in the field, and samples will be collected for XRCT and SEM analysis. The samples will inform laboratory experimental parameters. Later fieldwork in the Teno Massif in Tenerife will focus on mapping spatial and temporal changes in textural indicators of magma flow, in order to reconstruct 4D flow patterns.