CAREER: The Effect of Bubbles on Magma Dynamics

职业：气泡对岩浆动力学的影响

• 批准号: 1454821
• 负责人: Christian Huber
• 金额: $ 51.87万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-02-01 至 2017-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1454821&HistoricalAwards=false
• 关键词: CAREER; Effect; Bubbles; Magma; Dynamics

Volcanoes have exerted a fascination since the dawn of civilization. Eruptions, besides their obvious associated hazards, are one of the rare expressions of the dynamics of the Earth over timescales that are easy to comprehend from our standpoint. Over the last decades, our community has recognized the importance of exsolved volatiles (gas bubbles) on the chemical and physical evolution of magmas in the shallow crust and on eruption dynamics. The complexity of volcanic processes and our inability to observe directly how magmas evolve prior and during volcanic eruptions has seriously limited our ability to predict the timing and behavior of volcanic eruptions. With this project, we propose the development of new numerical methods, complemented with fluid dynamics experiments to provide a quantitative understanding of how the exsolution of gases affects the physical properties of magmas, their chemistry (and the composition of gases released to the atmosphere) and ultimately how bubbles behave collectively and affect the behavior of magmas erupting at the Earth surface.Magmas are multiphase systems composed of a very viscous ambient fluid (silicate melt), crystals and sometimes complemented by exsolved (immiscible) gas bubbles. In order to predict how magmas evolve before and during eruptions, we need to develop dynamic models that allow us to accurately represent the interplay between these three phases under various conditions. In this project, we plan to study first the exsolution and growth of water-rich bubbles to model their effect on chemical differentiation, i.e. how secondary gas phases such as sulfur species and CO2 partition into growing bubbles. The amount of sulfur incorporated into bubbles before an eruption is significant to quantify the impact of eruptions on climate (sulfur is a potent aerosol that affects the radiative balance in the atmosphere). The chemistry of the exsolved gas phase and its participation in a future eruption depend on the efficiency of phase separation in magmas and the possible accumulation of gas bubbles in parts of the reservoir that are more likely to erupt (lower viscosity). Our second task is to study the physics of phase separation, bubble-crystals-melt, more specifically to understand how the magma motion is impeded or facilitated by the presence of discrete bubbles and crystals. Finally, once the rheology of multiphase magmas is better constrained, we plan to use these results and study how buoyant gas bubbles migrate in zoned magma reservoirs. The question we aim to answer is whether bubbles are prone to accumulate in regions of low or high crystal content and how this accumulation affects the chemistry of the gas in the bubbles and the eruptive behavior of the magma.The results of the proposed research will have broad implications for physical volcanology, petrology, geochemistry and fluid dynamics. It will provide quantitative constraints on the state of magmas stored in shallow crustal reservoirs and also provide a better account of the effect of bubbles on magmas as they ascend to the surface during eruptions. Predictive models for the exsolution of sulfur in magmatic systems can also provide clues as to the climate impact of pre-historical large explosive eruptions (e.g. Toba, Cerro Galan). The goal of the proposed research is to provide quantitative tools and constitutive relations that will be widely available to interpret existing datasets (geochemistry of magmas, rheological experiments on magmas) and transfer this new knowledge to models of magma dynamics. Additionally, the development of new numerical methods to study multiphase fluid dynamics will impact the Computational Fluid Dynamics community and other fields in science and engineering, where particle suspensions or bubble emulsions are important (e.g. effect of fluid dynamics on biology, food processing?)

自人类文明诞生以来，火山就一直具有魅力。火山爆发，除了其明显的相关危害之外，是地球在时间尺度上的动力学的罕见表现之一，从我们的角度来看很容易理解。在过去的几十年里，我们的社会已经认识到的重要性，出溶挥发物（气泡）的化学和物理演化的岩浆在地壳浅部和喷发动力学。火山活动过程的复杂性以及我们无法直接观察火山爆发前和火山爆发期间岩浆的演化，严重限制了我们预测火山爆发时间和行为的能力。通过这个项目，我们提出了新的数值方法的发展，补充流体动力学实验，以提供定量的了解气体的出溶如何影响岩浆的物理性质，他们的化学（以及释放到大气中的气体成分）以及气泡如何集体行为并最终影响岩浆在地球表面喷发的行为。岩浆是多相系统，非常粘稠的环境流体（硅酸盐熔体）、晶体，有时还伴有出溶（不混溶）气泡。为了预测岩浆在喷发之前和喷发期间如何演化，我们需要开发动态模型，使我们能够准确地表示这三个阶段在各种条件下的相互作用。在这个项目中，我们计划首先研究富水气泡的出溶和生长，以模拟它们对化学分化的影响，即二次气相（如硫物质和CO2）如何分配到不断增长的气泡中。火山爆发前气泡中的硫含量对于量化火山爆发对气候的影响至关重要（硫是一种影响大气中辐射平衡的强效气溶胶）。 出溶气相的化学性质及其在未来喷发中的参与程度取决于岩浆中相分离的效率以及储层中更有可能喷发的部分（粘度较低）中气泡的可能积聚。 我们的第二个任务是研究相分离的物理学，气泡-晶体-熔体，更具体地说，是为了了解离散气泡和晶体的存在如何阻碍或促进岩浆运动。 最后，一旦多相岩浆的流变学得到更好的约束，我们计划使用这些结果，并研究如何浮力气泡迁移分区岩浆储层。我们的目标是回答的问题是，气泡是否容易积聚在低或高晶体含量的区域，以及这种积聚如何影响气泡中气体的化学性质和岩浆的喷发行为。拟议的研究结果将对物理火山学，岩石学，地球化学和流体动力学产生广泛的影响。它将提供定量约束的状态下储存在地壳浅水库的岩浆，也提供了一个更好的帐户泡沫的岩浆，因为它们上升到表面在喷发。岩浆系统中硫出溶的预测模型也可以为史前大型爆炸性喷发（例如多巴，Cerro Galan）的气候影响提供线索。拟议研究的目标是提供定量工具和本构关系，将广泛用于解释现有的数据集（岩浆地球化学，岩浆流变学实验），并将这种新的知识转移到岩浆动力学模型。此外，研究多相流体动力学的新数值方法的发展将影响计算流体动力学社区和其他科学和工程领域，其中颗粒悬浮液或气泡乳液很重要（例如流体动力学对生物学的影响，食品加工？）