Constraining properties of pyroclastic density currents with remote infrasound and seismic observations

火山碎屑密度流(PDC)是火山喷发产生的颗粒和气体的高温混合物，它们沿地面横向运动。PDCs通常是由喷发柱或熔岩穹隆坍塌产生的，由负浮力驱动。由于它们的流动性、快速的速度和高温，PDC是最危险的火山现象，造成了50%以上的与火山有关的死亡。PDC也很难直接观察。除了它们的危险性质外，PDC很少发生，而且通常位于偏远和不适宜居住的地方。此外，由于复杂的内部动力学被视觉上不透明的流体所遮挡，通常只能对流动的外壳进行直接的肉眼观察。因此，我们对这些多相湍流的了解大多来自对PDC矿床的地质观测、实验室研究和数值模型。这项工作通过将物理过程与地震波和次声波联系起来，扩展了对PDC动力学的了解。地球物理观测(次声和地震)可在离PDC活动安全距离处进行，并可提供有关PDC动态的高分辨率信息。该项目还支持一名博士后学者，他将参与将STEM和自然灾害资源带到卡斯卡迪亚地区学校的活动。为了这个项目，我们将开发一个量化框架，将PDC的性质和动力学与地球物理观测数据联系起来。研究人员将对PDCS进行3D多相模拟，并计算次声和地震辐射。这将使调查人员能够直接将模拟输出与现场数据进行比较，这将为验证和改进PDC动力学的数值模型提供一种方法。研究人员将进行敏感性分析，以了解地球物理观测值对哪些特性敏感，并将探索已被证明对PDC动力学重要的不同物理过程的地球物理信号，如夹带和流态化。这项拟议的工作将增加对控制PDC的过程的基本科学理解，并将通过在地球物理观测数据和流动特性之间建立定量联系来帮助数据解释和火山监测工作。这一奖项反映了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。

Pyroclastic density currents (PDCs) are hot mixtures of eruption-derived particles and gas that move laterally along the ground. PDCs are commonly generated by eruption column or lava dome collapse and are driven by negative buoyancy. Due to their mobility, rapid velocities, and high temperatures, PDCs are the most hazardous volcanic phenomena and are responsible for over 50% of volcanic-related fatalities. PDCs are also challenging to observe directly. In addition to their hazardous nature, PDCs occur infrequently and often are located in remote and inhospitable places. Furthermore, direct visual observations can usually only be made of the outer shell of the flow as the complex internal dynamics are obscured by visually opaque fluid. Therefore, most of our understanding about these multiphase, turbulent flows comes from geological observations of PDC deposits, laboratory studies and numerical models. This work extends knowledge of PDC dynamics by associating physical processes with seismic and infrasonic waves. Geophysical observations (infrasound and seismic) can be made at safe distances from PDC activity and can provide high-resolution information about PDC dynamics. This project also supports a postdoctoral scholar, who will engage in activities that bring STEM and natural hazard resources to schools in the Cascadia region.For this project we will be developing a quantitative framework to relate PDC properties and dynamics to geophysical observables. The researchers will perform 3D multiphase simulations of PDCs and compute the infrasound and seismic radiation. This will enable the investigators to directly compare the simulation outputs with field data, which will provide a way to validate and improve numerical models of PDC dynamics. The researchers will perform a sensitivity analysis to understand what properties the geophysical observables are sensitive to and will explore the geophysical signals of different physical processes that have been shown to be important to PDC dynamics, such entrainment and fluidization. The proposed work will increase fundamental scientific understanding about the processes governing PDCs and will aid in data interpretation and volcano monitoring efforts by developing quantitative links between geophysical observables and flow properties.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.