NSFGEO-NERC Quantifying disequilibrium processes in basaltic volcanism

玄武岩火山作用是太阳系中最常见的火山作用形式。在地球上，火山喷发会影响全球和区域气候，并通过火山灰、气体和熔岩的排放威胁到生活在火山阴影下的人口。冰岛火山爆发对英国的具体风险被认为是国家民事紧急情况风险登记册中四个“最高优先级风险”之一。火山喷发的影响取决于强度和类型，从爆炸性和富含火山灰（影响空域通道和气候）到喷涌性和富含气体（影响本地和远程的公共卫生和作物/牲畜）。了解这些喷发方式及其在时间和空间上的演变是预测喷发影响的关键。喷发方式受岩浆上升过程中气体与岩浆的耦合程度控制，强耦合导致破碎和灰的生成加剧。这种耦合是由几个非线性过程的相互作用和反馈控制的：多相岩浆粘度演化、结晶、气体析出、渗透率、岩浆上升速度和动态岩浆管道系统中的破碎。这种非线性产生了复杂的行为。因此，了解控制喷发方式的过程对火山学和喷发预测至关重要。先前工作的一个关键限制是，它几乎完全基于熔体、晶体和挥发物之间的平衡假设。换句话说，火山学界传统上认为岩浆的脱气和凝固/结晶过程几乎是在岩浆上升和喷发过程中的减压过程中瞬间发生的。然而，现在人们认识到，达到晶体生长和挥发性析出平衡所需的时间尺度与玄武岩岩浆喷发的上升时间相似或更长，因此不平衡是普遍存在的。因此，不平衡过程是阻碍定量建模和理解火山过程及其影响的关键缺失环节。NERC-NSF DisEqm项目的核心目标是创建一个经验约束的玄武岩火山不平衡过程的定量描述，并通过一个新的数值模拟框架将其应用于解决关键的火山学问题。为了实现这一目标，我们召集了一个世界领先的团队来进行实验，使用新的，突破性的同步加速器x射线成像和流变性技术来可视化和量化结晶，脱气和多相。高压高温粘度的演变，彻底改变了高温高压实验岩石学和高温高压流变学领域。地球化学限制将通过应用最先进的岩石学分析技术对光束线和台式淬火实验中产生的样品进行分析来实现。我们将进行大规模的流体动力学模拟，以告知和验证三维数值模拟，我们将通过实地研究来约束破碎和喷发柱过程。结果将被整合到一个最先进的数值模型中，并应用于冰岛、美国和意大利玄武岩喷发的影响集中案例研究。总之，我们的项目将在我们对岩浆上升过程中的不平衡过程的理解和我们对玄武岩喷发现象的建模能力方面产生范式转变，从而在我们预测和量化玄武岩喷发影响的能力方面产生一步变化。

Basaltic volcanism is the most common form of volcanism in the solar system. On Earth, eruptions can impact global and regional climate, and threaten populations living in their shadow, through a combination of ash, gas and lava emissions. The specific risk to the UK from an Icelandic eruption is recognized as one of the four 'highest priority risks' in the National Risk Register of Civil Emergencies. The impact of an eruption is determined by both intensity and style, ranging from explosive and ash-rich (impacting on air-space access and climate) to effusive and gas-rich (affecting public health and crops/livestock locally and distally). Understanding these eruptive styles, and their evolution in time and space is key to forecasting the impacts of eruptions.Eruption style is controlled by the degree of coupling between gas and magma during magma ascent, with strong coupling leading to enhanced fragmentation and ash production. This coupling is controlled by the interplay and feedback among several non-linear processes: multi-phase magma viscosity evolution, crystallisation, gas exsolution, permeability, magma ascent velocity and fragmentation within a dynamic magma plumbing system. Such non-linearity produces complex behaviour. Understanding the processes controlling eruptive style is therefore critical for volcanology and eruption forecasting. A crucial limitation of previous work is that it has been predicated almost exclusively on the assumption of equilibrium between melt, crystals and volatiles. In other words, the volcanology community has conventionally assumed that the processes of magma degassing and solidification/crystallisation occur nearly instantaneously in response to depressurisation during magma ascent and eruption. However, it is now recognised that the timescales required to achieve equilibrium for both crystal growth and volatile exsolution are similar to or longer than ascent times for erupting basaltic magmas, and therefore disequilibria are ubiquitous. Disequilibrium processes are therefore a key missing link preventing quantitative modelling and understanding of volcanic processes, and their impacts.The core aim of the NERC-NSF DisEqm project is to create an empirically-constrained quantitative description of disequilibrium processes in basaltic volcanism, and to apply this to address key volcanological problems through a new numerical modelling frameworkIn order to meet this aim, we bring together a world-leading team to perform experiments using new, ground-breaking synchrotron X-ray imaging and rheometric techniques to visualise and quantify crystallisation, degassing and multiphase, HPHT (high-pressure, high-temperature) viscosity evolution, revolutionising the fields of HPHT experimental petrology and HPHT rheometry. Geochemical constraints will be achieved by applying state of the art petrological analytical techniques to samples produced both on the beamline and in benchtop quench experiments. We will perform large-scale fluid dynamics simulations to inform and validate the 3D numerical modelling, and we will constrain fragmentation and eruption column processes with empirical field studies. Results will be integrated into a state-of-the-art numerical model, and applied to impact-focussed case studies for Icelandic, US and Italian basaltic eruptions. In conclusion, our project will produce a paradigm shift in our understanding of disequilibrium processes during magma ascent and our capacity for modelling basaltic eruption phenomena, creating a step-change in our ability to forecast and quantify the impacts of basaltic eruptions.