Collaborative Research: Linking pyroclastic surge dynamics and deposits through integration of field data, multiphase numerical modeling, and experiments

爆炸性的火山喷发释放出称为火山碎屑涌流的热气和颗粒；这些对人类是致命的，并严重破坏或摧毁建筑物和其他基础设施。在美国境内，火山碎屑潮在许多地区是一个潜在的危险，比如西南部和太平洋西北部的喀斯喀特山脉沿线。了解速度、压力、温度和颗粒浓度等参数对于预测火山碎屑涌浪危险和采取缓解措施是必要的。测量活跃的火山碎屑涌流基本上是不可能的，因为它们不可预测，而且它们造成了极端的条件。因此，我们必须使用间接方法：(1)对火山碎屑涌产生的沉积物进行详细研究，这可以在火山平静后进行研究；(2)旨在复制火山涌的某些方面的实验；以及(3)流动的计算机模拟。本项目反复使用这三种方法。这项工作将为预测和减轻火山灾害提供新的见解和工具。此外，这项工作将由一个多元化的、新组建的多所大学团队完成，将培训两名新的博士生，并将加强学术研究人员与美国地质调查局之间的合作伙伴关系，美国地质调查局主要负责风险评估。对火山碎屑涌流沉积中局部相发育的控制，以及更大规模的参数，如近端到远端的相变化、跳动和损害潜力，人们知之甚少。我们将解决以下研究问题：(1)在局部尺度(例如，单个露头或露头群)，河床形态和相与悬移质、推移质通量和局部地形的沉积有什么关系？(2)在大尺度(近端到远端)，沉积、地形、初始温度、质量通量和大气夹带对大尺度相分布、冲刷距离和破坏潜力的作用是什么？拟议的工作包括三个组成部分。(1)详细的实地研究将侧重于两个保存完好的年轻沉积物(加利福尼亚州乌贝海贝火山和索诺拉埃勒甘特火山口)，并记录相、粒度和成分随喷口距离和当地地形环境的变化。(2)试验将检验和推广野外可测的沙丘形态参数、推移质通量和悬移质泥沙通量之间的简单关系。(3)多相数值模拟将使用自适应网格加密来求解床层附近的通量，将改进气体与超细灰之间耦合的数值解(这是涌浪输运和沉积的关键)，并将使用非结构网格技术来模拟复杂自然地形上的涌浪输送。由该项目产生的新的多阶段建模工具将广泛用于研究社区。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。

Explosive volcanic eruptions unleash flows of hot gases and particles called pyroclastic surges; these are deadly to humans and severely damage or destroy buildings and other infrastructure. Within the United States, pyroclastic surges are a potential hazard in many areas such as the Southwest and along the Cascade Range of the Pacific Northwest. Understanding parameters such as speed, pressure, temperature, and particle concentration is necessary to predict pyroclastic surge hazards and to take mitigative measures. Measurements of active pyroclastic surges are essentially impossible because of their unpredictability and the extreme conditions they create. As a result, we must use indirect methods: (1) detailed study of the deposits that were produced by pyroclastic surges, which can be studied after a volcano has gone quiet; (2) experiments aimed at replicating some aspects of the surges; and (3) computer modeling of the flows. This project uses these three methods iteratively. The work will provide new insights and tools to use in forecasting and mitigating volcanic hazards. In addition, the work will be done by a diverse, newly-formed multi-university team, will train two new Ph.D. students, and will strengthen partnership between academic researchers with the U.S. Geological Survey, which has primary responsibility for hazard assessment.Controls on the development of local facies in pyroclastic surge deposits as well as larger-scale parameters such as proximal-to-distal facies variations, runout, and damage potential are poorly understood. We will address the following research questions: (1) At the local scale (e.g., individual outcrop or group of outcrops), what are the relationships of bed forms and facies to sedimentation from suspended load, bed load flux, and local topography? (2) At the large scale (proximal to distal), what are the roles of sedimentation, topography, initial temperature, mass flux, and atmospheric entrainment on large-scale facies distribution, runout distance, and damage potential? The proposed work includes three components. (1) Detailed field studies will focus on two well-preserved, young deposits (Ubehebe volcano, California; Crater Elegante, Sonora), with documentation of facies, grainsize, and componentry as functions of distance from vent and local topographic setting. (2) Experiments will test and extend a simple relationship between dune-form parameters measurable in the field, bed load flux, and suspended load sedimentation flux. (3) Multiphase numerical modeling will use adaptive mesh refinement to resolve fluxes near the bed, will improve the numerical solution of coupling between gas and very fine ash (key for surge transport and deposition), and will use unstructured mesh technology to model surge transport over complex natural terrains. A new multiphase modeling tool that results from the project will be available for the research community at large.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.