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

在十年的时间尺度上，对人类产生重大影响的自然灾害之一是高度爆炸性的普林尼火山喷发，其动力学被认为与岩浆气体（如水和二氧化碳）从喷发的岩浆中逸出的方式密切相关。岩浆脱气始于气泡的成核，这些气泡以囊泡的形式保存在喷发的火山岩碎片中。人们认为，在给定体积的火山岩中气泡的数量和大小提供了驱动气泡成核的力的记录，并由此推断出喷发的动力学。具体来说，岩浆上升到地表的速度，从而经历减压，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在一立方毫米的岩浆中在几分之一秒到几秒钟内形成核。这种在高压下从溶解气体到气态气泡的转变是爆炸性喷发的关键机制。目前关于爆炸喷发期间气泡成核速率的模型是基于经典成核理论的。在条件（压力、减压速率、成分、溶解气体含量、温度）是已知和可控的情况下，对岩浆中气泡成核的实验室实验进行了初步分析，结果表明，这一经典理论无法预测气泡在各种条件下的成核速率。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可达到的物理速率，从而高估了岩浆上升速率。该项目的目标是获得速率泡成核的新公式，该公式将适用于与爆炸性火山爆发有关的各种条件。这将通过一项综合研究来完成，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。本研究的结果，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，从而提高其预测能力。这些模型，反过来，将用于解决岩浆减压率和在给定体积的岩浆内形成核的气泡数量之间的精确关系的问题，从而使基于观测的研究与通过数值模拟和危害评估的定量预测更加可靠地结合起来。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。由于该项目将整合经典成核理论不足的其他领域的最新进展，它将推动最先进的技术，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.