EAR-PF: TURBULENT AIR ENTRAINMENT IN PYROCLASTIC DENSITY CURRENTS

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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.