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、流出距离长、温度高、体积大。有人提出，它们的长跳动距离可能是由于流化。流化气体也可能是细颗粒的洗脱作用和巨大的co- ignbrite羽状物的产生的原因，这些羽状物覆盖了移动的气流。这些羽流产生了历史上最显著的气溶胶和火山灰注入平流层。有趣的是，只需要相对较小的气流速度就可以使火山灰流化。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，这些热碎片床由于剪切应力而变形和/或由于颗粒碰撞而膨胀。特别令人感兴趣的是，周围的空气是否被热颗粒的膨胀床所吸收，以及这种气流是否能使存在于较大岩石碎片之间的细颗粒流化和/或洗脱，这些细颗粒会影响火山碎屑流的流动性。将用于实验的设备产生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。缩放无量纲参数将用于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动力学，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进行，并将为研究生和本科生提供培训。为了涉及更多的人，拓宽研究的视角，将提供基于本提案中所讨论的主题的研究生水平课程。该项目还将导致工程和火山学界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.