EAR-PF: TURBULENT AIR ENTRAINMENT IN PYROCLASTIC DENSITY CURRENTS

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。本杰明·安德鲁斯被授予美国国家科学基金会地球科学博士后奖学金，以在伯克利大学开发一个综合的研究和教育项目。他的调查将集中在火山碎屑致密流上，这是火山喷发的一种常见且具有潜在破坏性的危险。当火山喷发时，浮石、火山灰和气体的混合物比大气更稠密，可以以每小时100英里以上的速度沿着火山的侧翼移动。对火山碎屑密度流中卷吸空气过程的定量认识对于理解和预测水流行为是至关重要的。尽管以前的研究考察了密度流，但大多数实验室实验都被不适当地缩放以适用于火山碎屑流，或者忽略了夹带流体的膨胀，许多计算模型将夹带视为一个恒定速率过程。这项研究考察了火山碎屑密度流中的湍流夹带，目的是将夹带和湍流与流动温度、喷发速率、颗粒大小和密度定量地联系起来。在拟议的实验中，空气中含有热的细粒的密度流将被引导通过充满空气的储罐来模拟火山碎屑密度流的传输。在模拟过程中，储罐中的仪器将监测流动结构、速度场和温度，并在模拟后测量产生的沉积物厚度。根据这些数据，安德鲁斯博士将描述空气夹带如何随时间、空间和颗粒特性而变化，以及它如何受到局部湍流速度场的控制。通过改变喷发速度和颗粒大小、密度和温度，实验将模拟火山碎屑密度流，并捕捉夹带和膨胀的动力学。这项研究对火山灾害预测和缓解有重大好处，因为火山碎屑流可以摧毁其路径上的任何东西，而火山灰羽流可能对航空构成重大威胁。拟议的实验将是第一次定量研究火山碎屑密度流中的空气卷吸和密度演化。这项研究的结果将改善对火山碎屑密度流部署在哪里，它们移动的速度有多快，以及火山灰羽流上升到多高的预测。通过这项研究，本科生将被介绍到野外和实验室工作。安德鲁斯博士将在拉森火山国家公园领导为期一周的本科生野外课程，目标是教授野外火山学方法，并促进学生对火山碎屑矿床的研究。两名学生将通过伯克利的本科生研究学徒计划直接参与火山碎屑密度流实验。这些学生将学习对夹带和流动行为的具体控制，然后将他们的研究项目发展成荣誉论文。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Benjamin Andrews is awarded an NSF Earth Sciences Postdoctoral Fellowship to develop an integrated program of research and education at Berkley University. His investigation will focus on pyroclastic density currents, a common and potentially devastating hazard of volcanic eruptions. When erupted, mixtures of pumice, ash, and gas are denser than the atmosphere, and can travel down the flanks of volcanoes at speeds in excess of 100 miles per hour. Quantitative knowledge of air entrainment processes in pyroclastic density currents is critical to understanding and predicting current behaviors. Although previous studies have examined density currents, most of those laboratory experiments have been improperly scaled for application to pyroclastic flows or ignored expansion of entrained fluid, and many computational models have treated entrainment as a constant rate process. This research examines turbulent air entrainment in pyroclastic density currents with the goals of quantitatively relating entrainment and turbulence to flow temperature, eruption rate, and particle size and density. In the proposed experiments, density currents comprising hot, fine-grained particles in air will be directed through an air filled tank to simulate pyroclastic density current transport. Instruments in the tank will monitor the flow structure, velocity field, and temperature during simulations, and measure the resulting deposit thicknesses after simulations. From those data, Dr. Andrews will describe how air entrainment varies with time, space, and particle properties, and how it is controlled by the local, turbulent velocity field. By varying eruption rates and particle sizes, densities, and temperatures the experiments will model pyroclastic density currents and capture the dynamics of entrainment and expansion. This research has significant benefits for volcanic hazard prediction and mitigation, as pyroclastic flows can destroy anything in their paths, and ash plumes can pose a significant threat to aviation. The proposed experiments will be the first quantitative study of air entrainment and density evolution within pyroclastic density currents. The results of this research will improve predictions of where pyroclastic density currents are emplaced, how fast they travel, and how high ash plumes ascend. Undergraduate students will be introduced to both field and laboratory work through this research. Dr. Andrews will lead a week-long undergraduate field course at Lassen Volcanic National Park with the goals of teaching field volcanology methods and facilitating student research on pyroclastic deposits. Two students will be directly involved in the pyroclastic density current experiments through Berkeley's Undergraduate Research Apprentice Program. Those students will study specific controls on entrainment and flow behavior, and then develop their research projects into honors theses.