Air Circulation Within Beds of Hot Fragments and Mobility of Pyroclastic Flows

火山碎屑流是最致命的火山现象之一，因为它们的速度快，运行距离长，温度高，体积大。有人提出，它们的长距离跳跃可能是由于流态化作用。流态化的气体也可能是细粉的淋滤和巨大的共燃烟柱的产生的原因，这些烟柱覆盖了流动的流动。这些羽状物产生了历史上最重要的气溶胶和火山灰注入平流层。有趣的是，只有相对较小的气流速度才能使火山灰流动。该项目的目标是用实验方法研究影响热碎片床内气流产生的基本过程和变量，热碎片床因剪应力而变形和/或因颗粒碰撞而膨胀。尤其令人感兴趣的是，周围的空气是否被热颗粒的膨胀床吸入，以及这种气流是否可以流态化和/或淋洗细粉，这些细粉在较大的岩石碎片之间的存在会影响火山碎屑流的流动性。将用于实验的装置制作了火山碎屑流的比例模型，其温度、间隙流体压力和间隙流体速度可以分别使用热电偶、压力传感器和流量计进行监测。标度无量纲参数将被用来将实验室中的过程与自然界中的过程联系起来。该项目将有助于更好地了解火山碎屑流的动力学，并因此对减轻和预测火山灾害具有重要意义。该项目将由一名博士后负责，并将为研究生和本科生提供培训。为了让更多的人参与并拓宽研究的视野，将开设一个以本提案所述主题为基础的研究生级别课程。该项目还将促成工程学和火山学社区之间新的跨学科合作。

Pyroclastic flows are among the deadliest of volcanic phenomena because of their high velocities, long run-out distances, high temperatures and large volumes. It has been suggested that their long run-out distances could be due to fluidisation. The fluidising gases are also probably responsible for the elutriation of fines and the generation of the giant co-ignimbrite plumes that override moving flows. These plumes produced the most historically significant injections of aerosol and ash into the stratosphere. Interestingly, only relatively small airflow velocities are necessary to fluidise volcanic ash. The goal of this project is to study with an experimental approach the fundamental processes and variables that affect airflow generation within beds of hot fragments that deform because of shear stresses and/or expand because of particle collisions. Of particular interest is whether ambient air is ingested by expanded beds of hot particles and whether this airflow can fluidise and/or elutriate the fines whose presence between larger rock fragments can affect the mobility of pyroclastic flows. The apparatus that will be used for the experiments produces scale models of pyroclastic flows whose temperature, interstitial fluid pressure and interstitial fluid velocity can be monitored using thermocouples, pressure transducers and flowmeters respectively. Scaling dimensionless parameters will be used to relate the processes in the lab to those in nature. This project will lead to a better understanding of pyroclastic flows dynamics and if thus of importance in the mitigation and forecast of volcanic hazards. This project will be carried out by one postdoc and will provide training for graduate and undergraduate students. In order to involve a larger number of persons and broaden the perspective of the research, a graduate level class based on the topics addressed in this proposal will be offered. This project will also lead to new interdisciplinary collaborations between the engineering and volcanology communities.