Magma Waves, magma wagging and volcanic oscillations

火山是动态的，甚至在喷发之前就显示出范围广泛的活动。许多火山，尤其是那些最具破坏性的火山，在地面膨胀、气体排放和地震活动方面经历了漫长而缓慢的振荡，在重复的高峰活动之间有几个小时到几天的周期。火山也可能经历震颤或震动，时间短得多，大约在一秒钟左右。这种振荡，有一天和第二长的周期，可以持续数周，直到火山爆发，因此是火山灾难的重要先兆。因此，了解这些振荡的原因对于预测这些灾难以及推进火山如何工作的科学至关重要。该项目旨在统一两种主要的物理模型，用于缓慢的超长振荡，即长一天的周期振荡和火山震颤，具有秒长的振荡周期。我们的模型解释了在充满岩浆的火山管道中缓慢上升的岩浆波气体脉冲的长周期振荡，这些脉冲依次到达地表，导致地面膨胀和其他活动，如小地震。这种较短周期的震动可以用岩浆摆动机制来解释，在这种机制中，火山导管中的重岩浆柱在一个由超气泡岩浆组成的海绵状外壳内左右摆动。然而，非常长的和较短的周期振荡并不是相互独立的；例如，长周期振荡涉及增强的火山震颤活动周期。该项目的主要目标是建立一个火山管道中气泡岩浆的三维模型，以解释从快速震颤到超慢周期的振荡行为的全部范围。本研究的中心假设是岩浆波的三维演化影响岩浆摇摆运动的发生；这可能为长周期振荡如何演变和触发（并维持）爆发前的短周期火山震颤提供了预测。该项目还涉及发展两相物理的基本理论，这些理论除了对火山灾害的影响外，可能有助于更好地了解地质、环境和与能源有关的过程的其他问题。岩浆波和岩浆摆动模型是根据两相系统的相同物理原理建立的；这些模型所描述的过程不可避免地是耦合的，并且相互影响对方的行为。例如，长周期的脱气活动与震颤有关，我们的模型表明气体排放有助于驱动震颤活动。此外，目前的岩浆波模型只考虑了一维的垂直运动，而目前的岩浆摆动模型只考虑了一维的水平运动。然而，新的初步模型已经表明，岩浆的摆动涉及到可以从地震台站检测到的圆形旋转运动。岩浆波也可能形成三维形状，如火山导管中心附近的球形袋，或导管壁附近伸展的带；这些波的形状会影响岩浆柱左右摆动的方式。因此，本提案的主要工作是：(1)发展岩浆波和岩浆摆动的三维两相分析理论，包括气体析出和变粘度等新物理；(2)建立了岩浆波与晃动演化活动完全耦合的三维统一数值模型；(3)用新的实验室实验，以及现有的地震学、地面运动和气体通量数据，包括最近在墨西哥一座火山的一个试点项目的观测结果，来检验模型的预测。这项工作的目标是提供物理理解，理想情况下，用统一的理论来预测导致火山爆发的长周期和短周期振荡的原因和演变。岩浆波和岩浆摆动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组成部分。将这些模型扩展到具有更复杂物理的三维空间，并最终统一为一个单一的数值模型，将提供丰富的预测，以进一步用实验室实验以及现有和新的数据测试模型。该模型将为火山喷发前火山岩浆柱的动力学和演化提供洞见，同时也为火山灾害提供潜在的重要预测工具。

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.