Magma Waves, magma wagging and volcanic oscillations

岩浆波、岩浆摇摆和火山振荡

基本信息

批准号：
1645057
负责人：
David Bercovici
金额：
$ 54.3万
依托单位：
Yale University
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-04-01 至 2022-03-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1645057&HistoricalAwards=false
关键词：
Magma Waves magma wagging volcanic

项目摘要

Volcanoes are dynamic and display a wide range of activity even before they erupt. Many volcanoes, especially the most destructive ones, undergo long slow oscillations in ground swelling, gas emissions and seismic activity, with periods between repeated peak activity of hours to days. Volcanoes may also experience tremor or shaking with much shorter periods of around one second. Such oscillations, with both day- and second-long periods, can last for weeks before an eruption occurs, and thus serve as important precursors to volcanic disasters. Understanding the cause for these oscillations is therefore critical for forecasting these disasters as well as for advancing the science of how volcanoes work. This project seeks to unify two leading physical models for both the slow ultra-long, i.e., day-long, period oscillations and volcanic tremor, with second-long oscillation periods. Our model explains long-period oscillations in terms of slowly ascending magma waves of gas pulses in the magma-filled volcanic conduit, which arrive sequentially at the surface, causing ground swelling and other activity such as small earthquakes. The shorter-period tremors are explained by a magma wagging mechanism in which the heavy column of magma in the volcanic conduit wags side-to-side inside of a spongy jacket of extra-bubbly magma. However, very-long and shorter period oscillations are not independent of each other; for example, long period oscillations involve cycles of enhanced volcanic tremor activity. The main goal of this project is to develop a 3-D (three-dimensional) model of bubbly magma in a volcanic conduit to account for the full range of oscillatory behavior, from rapid tremor to ultra-slow cycles. The central hypothesis of this study is that the evolution of magma waves in 3-D influences the onset of magma-wagging motion; this potentially provides a prediction for how long-period oscillations evolve and trigger (and sustain) shorter-period volcanic tremor prior to an eruption. The project also involves development of fundamental theories of two-phase physics that will, in addition to its impact on volcanic hazards, may contribute to better understanding of other problems of geological, environmental and energy-related processes.The models of magma waves and magma wagging are built from the same physics of two-phase systems,; the processes these models describe are inevitably coupled and influence each other's behavior. For example, degassing activity during long period cycles correlates with tremor, and our models suggest that gas emissions help drive tremor activity. Moreover, the current magma-wave model accounts for only vertical motion in one dimension, while the present magma-wagging model treats only horizontal movement in one-dimension. However, new preliminary models already suggest that the magma wagging entails circular swirling motion that can be detected from seismic stations. Magma waves are also likely to develop three-dimensional shapes, like spherical pockets near the center of the volcanic conduit, or stretched out bands near the conduit wall; these wave shapes would then affect how the magma column wags side to side. Accordingly, the primary activity of this proposal is to (1) develop the 3-D two-phase analytic theories of magma waves and magma wagging, including new physics such as gas exsolution and variable viscosity; (2) develop a 3-D unified numerical model of fully coupled magma wave and wagging evolution and activity; and (3) test the model predictions against new laboratory experiments, as well as existing seismological, ground-motion and gas-flux data, including recent observations from a pilot project in a volcano in Mexico. The goal of this work is to provide physical understanding and, ideally, model forecasting with a unified theory for the cause and evolution of long and short period oscillations, leading up to explosive volcanic eruptions. The magma wave and magma wagging models form the essential building blocks for a complete model of long and shorter period oscillations prior to volcanic eruption. The extension of these models into three-dimensions with more sophisticated physics, and their eventual unification into a single numerical model, will provide a wealth of predictions to further test the model with lab experiments as well as existing and new data. The model will provide insight into the dynamics and evolution of the volcanic magma column prior to an eruption, as well as a potentially important prognostic tool for volcanic hazards.

火山是动态的，甚至在喷发之前就表现出广泛的活动。许多火山，尤其是最具破坏性的火山，会经历地面膨胀、气体排放和地震活动的长期缓慢振荡，其重复高峰活动的周期为数小时至数天。火山也可能会经历更短时间（大约一秒）的震动或晃动。这种具有一天和第二天的振荡，可以在喷发前持续数周，因此是火山灾害的重要前兆。因此，了解这些波动的原因对于预测这些灾害以及推进火山工作原理的科学至关重要。该项目旨在统一慢速超长周期振荡（即全天周期振荡）和火山震颤（具有第二长振荡周期）的两个主要物理模型。我们的模型用充满岩浆的火山管道中缓慢上升的气体脉冲岩浆波解释了长周期振荡，这些岩浆波依次到达地表，导致地面膨胀和其他活动，例如小地震。较短周期的震动可以通过岩浆摇摆机制来解释，其中火山管道中的重岩浆柱在超泡沫岩浆的海绵套内部左右摇摆。然而，超长周期振荡和短周期振荡并不是相互独立的。例如，长周期振荡涉及火山震颤活动增强的周期。该项目的主要目标是开发火山管道中气泡岩浆的 3D（三维）模型，以解释从快速震颤到超慢周期的全方位振荡行为。这项研究的中心假设是，岩浆波的 3-D 演化影响岩浆摇摆运动的开始；这有可能为火山喷发前长周期振荡的演变以及触发（和维持）短周期火山颤动提供预测。该项目还涉及两相物理学基础理论的发展，除了对火山灾害的影响外，还可能有助于更好地理解地质、环境和能源相关过程的其他问题。岩浆波和岩浆模型摇摆是根据两相系统的相同物理原理构建的；这些模型描述的过程不可避免地耦合并影响彼此的行为。例如，长时间循环期间的脱气活动与震颤相关，我们的模型表明气体排放有助于驱动震颤活动。此外，当前的岩浆波模型仅考虑一维的垂直运动，而当前的岩浆摇摆模型仅考虑一维的水平运动。然而，新的初步模型已经表明，岩浆摇摆会产生圆形旋转运动，可以从地震台检测到。岩浆波也可能形成三维形状，例如火山管道中心附近的球形袋，或管道壁附近的延伸带；这些波浪形状会影响岩浆柱左右摇摆的方式。因此，该提案的主要活动是（1）发展岩浆波和岩浆摇摆的三维两相分析理论，包括气体析出和变粘度等新物理； (2) 开发全耦合岩浆波与摇摆演化和活动的三维统一数值模型； (3) 根据新的实验室实验以及现有的地震、地面运动和气体通量数据（包括墨西哥火山试点项目的最新观测结果）测试模型预测。这项工作的目标是提供物理理解，并在理想情况下，通过统一的理论对长周期和短周期振荡的原因和演化进行模型预测，从而导致火山喷发。岩浆波和岩浆摇摆模型构成了火山喷发前长周期和短周期振荡完整模型的基本构建模块。将这些模型扩展到具有更复杂物理原理的三维模型，并最终统一为单个数值模型，将提供丰富的预测，以便通过实验室实验以及现有数据和新数据进一步测试模型。该模型将深入了解火山喷发前岩浆柱的动态和演化，以及火山灾害的潜在重要预测工具。