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

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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.