Collaborative Research: A Self-consistent Model for Bubble Nucleation During Plinian Volcanic Eruptions

在十年的时间尺度上影响人类的重大自然灾害之一是高度爆炸性的普林尼安火山喷发，其动力学被认为与水和二氧化碳等岩浆气体从喷发的岩浆中逃逸的方式密切相关。岩浆脱气始于气泡的成核，气泡在喷发的火山岩碎片中以小泡的形式保存下来。人们认为，给定体积的火山岩中气泡的数量和大小记录了驱动气泡成核的力量，并由此推断出喷发的动力学。具体地说，岩浆上升到地表从而经历减压的速度和气泡成核的速度被认为是相关的，并影响喷发的爆炸强度。大约一百万个气泡可能会在一立方毫米的岩浆中成核，持续几秒到几秒。高压下从溶解气体到气泡的这种转变是爆发的关键机制。目前关于喷发过程中气泡成核速率的模型是基于经典成核理论的。对岩浆中气泡成核的实验室实验的初步分析表明，这一经典理论无法在广泛的条件下预测气泡的成核速度。在这些实验中，条件(压力、减压速率、成分、溶解气体含量、温度)是众所周知的，并且是可控的。这方面的一个基本问题是对减压速率的要求可能高于喷发期间实际可达到的速率，从而高估了岩浆上升的速率。该项目的目标是获得一种新的速率气泡成核公式，该公式将适用于与火山爆发相关的广泛条件。这将通过一项综合研究来实现，该研究包括硅酸盐熔体中气泡成核的实验室实验和这些实验的详细数值模拟。这项研究的结果，即硅酸盐熔体中气泡成核的新公式，将被纳入火山爆发的数值模型，从而增强它们的预测能力。反过来，这些模型将被用来解决岩浆减压速率与在给定体积的岩浆中成核的气泡数量之间的确切关系的问题，从而使基于观测的研究与通过数值建模和危险评估进行的定量预测更有力地结合在一起。此外，成核理论在许多学科中都很重要，例如化学工程和材料科学。由于这个项目将整合经典成核理论被发现不足的其他领域的最新进展，它将推动最新技术的发展，并有可能影响其他学科。

One of the large-impact natural hazards to affect humans on a decadal time scale are highly explosive Plinian volcanic eruptions, whose dynamics are thought to be intimately linked to the manner by which magmatic gases, such as water and carbon dioxide, escape from the erupting magma. Magma degassing begins with the nucleation of bubbles, which are preserved as vesicles in the erupted volcanic rock fragments. It is thought that the number and size of bubbles in a given volume of volcanic rock provide records of the forces that drive bubble nucleation and, by inference, the dynamics of the eruption. Specifically, the speed at which magma rises to the surface, thereby undergoing decompression, and the rate at which bubbles nucleate are thought to be correlated and affect the explosive intensity of an eruption. About one million bubbles may nucleate within a cubic millimeter of magma over fractions of a second to a few seconds. This transformation from dissolved gases to gaseous bubbles under high pressure is a key mechanism for explosive eruptions. Current models for the rate of bubble nucleation during explosive eruptions are based on Classical Nucleation Theory. A preliminary analysis of laboratory experiments of bubble nucleation in magmas, where conditions (pressure, rate of decompression, composition, content of dissolved gases, temperature) are well known and controlled, has shown that this classical theory fails to predict the rate at which bubbles nucleate across a wide range of conditions. A fundamental issue in this regard is the requirement for decompression rates that may be higher than physically attainable during an eruption, thus over-predicting rates of magma ascent.The objective of this project is to obtain a new formulation for the rate bubble nucleation, which will be applicable across a wide range of conditions of relevance to explosive volcanic eruptions. This will be accomplished through an integrated study that is comprised of laboratory experiments of bubble nucleation in silicate melts and detailed numerical modeling of these experiments. The result of this study, that is a new formulation for bubble nucleation in silicate melts, will be incorporated into numerical models of explosive volcanic eruptions, thereby enhancing their predictive capabilities. These models, in turn, will be used to resolve the question of what the precise relationship between magma decompression rate and the number of bubbles that nucleate within a given volume of magma is, thereby allowing a more robust integration of observationally based studies with quantitative predictions through numerical modeling and hazard assessment. Moreover, nucleation theory is of importance in a wide range of disciplines, such as for example chemical engineering and material science. Because this project will integrate recent advances in other fields where Classical Nucleation Theory has been found inadequate, it will advance the state-of-the-art and also have the potential to impact other disciplines.