Fluid oscillations in conduit-reservoir systems, very long period seismic signals at Kilauea volcano, and the phenomenology of unsteady magma ascent

火山喷发和与之相关的人类危害很难预测，因为它们涉及隐藏在地球表面下的高度不稳定的岩浆运动。尽管对推断地下岩浆运动至关重要的观测资料，如地震和次声，越来越多地被收集起来，但我们缺乏一个理论框架来理解产生这种信号的物理过程。这项工作将在短时间尺度上研究火山导管内的岩浆流动，以了解导致各种喷发现象的物理过程。第一个目标是研究夏威夷基拉韦厄火山的火山活动，这些活动与落入活跃熔岩湖的岩石有关，这会导致管道内岩浆的共振振荡，有时还会在地表发生小型但危险的爆炸。这些有据可查的自然实验为浅层管道和岩浆储集层几何模型以及多相岩浆流体性质提供了独特的测试。第二个目标是开发一个高性能的计算建模框架，以预测火山管道中岩浆在各种流动条件下的瞬时运动，包括在火山爆发期间。这项工作将有助于弥合地球物理观测、火山物理和先进计算之间的差距。该项目将支持研究生进行跨学科的科学研究，并为正在进行的“火山倾听项目”的发展做出贡献，这是一项致力于将火山数据表现为声音和动画的外展工作。该项目描述了一项关于火山管道中小幅度振荡岩浆流动的研究。第一个目标是研究夏威夷基拉韦厄火山的短期(数十分钟)动乱，这些动乱与岩石坠落到活跃的熔岩湖上和不断上升的气弹有关。这些扰动导致管道内多相岩浆的“非常长的周期”(VLP，5−40 S)振荡、爆炸、不稳定的地表气体通量和熔岩湖高度变化，这些都是在附近的地球物理仪器网络上记录下来的。这些有据可查的自然实验为非稳定管道流动模型提供了一种独特的测试，将用于反演地下管道和储集层几何以及岩浆流变性和原始挥发分含量。以前由美国国家科学基金会资助的工作开发了一个初步的框架，用于根据耦合管道-油藏系统的共振特征模式对VLP地震数据进行建模和反演，其中流体压力的变化会导致周围固体地球的弹性变形，并通过仪器记录下来。这一框架将适用于基拉韦厄Halema‘uma’u喷口十年寿命内的数千项活动。贝叶斯马尔科夫链蒙特卡罗反演将纳入来自地震活动、地面变形、持续重力、岩石学决定的熔体粘度和挥发分含量以及熔岩湖几何形状的约束。第二个目标是生成一个正演模拟框架，以预测岩浆流复杂状态下的波动。对气体和液体之间的相对运动进行建模将预测瞬时动荡事件期间的地表气体流量数据，以及落石引发的瞬时爆炸。还将在爆炸性喷发的背景下研究波状扰动，在爆炸性喷发期间，这种振荡的流体运动可能在喷发期间的状态变化中发挥关键作用，例如开始碎裂和爆炸行为。火山系统中的流动通常不会在这里提出的短时间尺度上进行研究。为了实现多个地球物理数据集之间的一致性，必须明确考虑非平衡气泡生长和再吸收、包括分支裂缝的复杂管道几何形状以及具有强界面(如气泡出溶或岩浆破碎)的分层多相流体流动。这种方法还允许对准定常管道流动模型进行关键检验，该模型可以被证明对扰动是条件线性不稳定的。这为研究喷发式转变提供了一种新的途径。最后，对强层结多相系统中不稳定波运动的研究将有助于数值方法的发展，其应用范围超出了火山学。利用可证明稳定的高阶有限差分方法的最新进展来数值解决流动不稳定性，为推进火山导管流动模型、发现新的喷发现象学以及与火山监测工作相联系提供了独特的机会。该项目将涉及俄勒冈大学的两名博士生，涉及地球科学和计算机科学。软件将是开源的，并可供社区使用。项目团队将访问并与美国地质调查局(USGS)合作研究基拉韦厄火山。正在进行的建模和地震数据分析结果将被纳入公开演讲和致力于将火山数据表现为声音和动画的“火山倾听项目”推广工作中。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Volcanic eruptions and the human hazards associated with them are challenging to predict because they involve highly unsteady motions of magma hidden below Earth’s surface. Although observations critical for inferring subsurface magma motions, such as seismicity and infrasound, are being collected more and more often, we lack a theoretical framework for understanding the physical processes that give rise to such signals. This work will be a study of magma flow within volcanic conduits on short timescales, in order to understand the physical processes that give rise to a variety of eruptive phenomena. The first goal is to study volcanic activity at Kilauea volcano, Hawai’i’, associated with rocks falling onto an active lava lake, which cause resonant oscillations of magma within the conduit and sometimes small but hazardous explosions at the surface. These well-documented natural experiments provide a unique test for models of the shallow conduit and magma reservoir geometry as well as multiphase magma fluid properties. The second goal is to develop a high performance computing-enabled modeling framework to predict transient motions of magma in volcanic conduits under a range of flow conditions, including during explosive eruptions. This work will help bridge the gap between geophysical observations, volcano physics, and advanced computing. The project will support graduate students in interdisciplinary scientific research, and contribute to ongoing development of “The Volcano Listening Project”, an outreach effort dedicated to representing volcano data as sound and animations.This proposal describes a study of small amplitude oscillatory magma flow in volcanic conduits. The first goal is to study short term (tens of minutes) unrest episodes at Kilauea volcano, Hawai’i’, associated with rock falls onto an active lava lake and from rising gas slugs. These disturbances cause ‘very long period’ (VLP, 5−40 s) oscillations of the multi-phase magma within the conduit, explosions, unsteady surface gas flux, and lava lake height variations, recorded on a nearby network of geophysical instruments. These well-documented natural experiments provide a unique test for unsteady conduit flow models, which will be used to invert for subsurface conduit and reservoir geometry as well as magma rheology and primary volatile content. Previous NSF-funded work developed a preliminary framework for modeling and inverting VLP seismic data in terms of the resonant eigenmodes of coupled conduit-reservoir systems, where fluid pressure changes cause elastic deformations of the surrounding solid Earth that are recorded instrumentally. This framework will be applied to thousands of events spanning the ten-year lifespan of the Halema’uma’u vent on Kilauea. Bayesian Markov-Chain Monte Carlo inversions will incorporate constraints from seismicity, ground deformation, continuous gravity, petrologically-determined melt viscosity and volatile content, and lava lake geometry. The second goal is to generate a forward modeling framework to predict wave motion in complex states of magma flow. Modeling relative motion between gas and liquid will predict surface gas flux data during transient unrest events, as well as transient explosions triggered by rockfalls. Wave-like disturbances will also be studied in the context of explosive eruptions, where such oscillatory fluid motions may play a key role in state shifts during eruptions such as the onset of fragmentation and explosive behavior. Flow in volcanic systems is typically not studied at the short timescales proposed here. Explicit consideration of non-equilibrium bubble growth and resorption, complex conduit geometry that includes branching cracks, and stratified, multiphase fluid flow with strong interfaces (such as bubble exsolution or magma fragmentation) is necessary to achieve consistency between multiple geophysical datasets. This approach also permits a critical examination of quasi-steady conduit flow models, which can be shown to be conditionally linearly unstable to perturbations. This suggests a new approach to studying transitions in eruption style. Finally, the study of unstable wave motions in strongly stratified multiphase systems will contribute to numerical method developments with applications beyond volcanology. Numerically resolving flow instabilities using recent developments in provably stable high-order finite difference methods provides a unique opportunity to advance models of volcanic conduit flow, discover new eruptive phenomenology, and connect with volcano monitoring efforts. The project will involve two PhD students at the University of Oregon across Earth Science and Computer Science. Software will be open-source and available to the community. The project team will visit and collaborate with the USGS (Hawaiian Volcano Observatory) to study Kilauea. Ongoing results of modeling and seismic data analysis will be incorporated into public presentations and to “Volcano Listening Project” outreach effort dedicated to representing volcano data as sound and animations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.