A novel experimental chamber for the characterization of free-falling particles in volcanic plumes.

Volcanic plumes pose a hazard to health and society and a particular risk for aviation. Hazard mitigation relies on forecasting plume dispersion within the atmosphere over time. The accuracy of forecasts depends on our understanding of particle dispersion and sedimentation processes, as well as on the accuracy of model input parameters, such as the initial particle size distribution and concentrations of volcanic particles (i.e., volcanic ash) in the atmosphere. However, our understating of these processes and the accurate quantification of input parameters remain the main sources of uncertainty in plume dispersion modeling. It is usually impractical to sample volcanic plumes directly, but particle sedimentation can be constrained in the laboratory. Here, we describe the design of a new experimental apparatus for investigating the dynamics of free-falling volcanic particles. The apparatus can produce a sustained column of falling particles with variable particle concentrations appropriate to a volcanic plume. Controllable experimental parameters include particle size distributions, types, and release rates. A laser-illuminated macrophotography system allows imaging of in-flight particles and their interactions. The mass of landing particles is logged to inform deposition rates. Quantitative measurements include particle morphology characterization, settling velocities, flow rates, and estimation of concentrations. Simultaneous observations of particle interaction processes and settling dynamics through direct control over a wide range of parameters will improve our parameterization of volcanic plume dynamics. Although the apparatus has been specifically designed for volcanological investigations, it can also be used to explore the characteristics of free-falling particle columns occurring in both environmental and industrial settings.

A novel experimental apparatus for investigating bubbly flows in a slot geometry.

Bubbly flows occur in a wide variety of industrial and environmental settings. While there is a broad literature that describes bubbly flow behavior in pipes and channels, flow in a high aspect ratio slot has received little attention. We describe the design and construction of a new experimental apparatus to investigate the processes associated with bubbly flows in a slot geometry. The apparatus is designed to perform scaled analog experiments to investigate the flow of bubbly magma through the sub-volcanic plumbing system, but it is sufficiently flexible to address many other flow scenarios. The main bubble column, which can be inclined up to 30° from the vertical, comprises a glass-walled slot 3 m wide and 2 m tall, with 3 cm gap width. A modular and flexible gas injection system allows the number, spacing, and diameter of the gas emission points to be varied, as well as gas injection flux, and a pumped recirculation system allows the concurrent liquid flow rate to be controlled and varied. A dedicated data acquisition system synchronizes high-speed videography with temperature and pressure data from different points in the apparatus. Preliminary data are presented to demonstrate the operation of the apparatus and to illustrate the types of fluid dynamic information that can be captured.