A Lab-Scale Experiment to Measure Terminal Velocity of Volcanic Ash

In this paper, a novel methodology to measure trajectoryand terminal velocity of volcanic ash in laboratory ispresented. The methodology consists of the following: 1) planninga lab-scale experiment in order to reproduce the sedimentationprocesses of fine volcanic ash based on the principle of dynamicsimilarity; 2) realizing the experimental setup using a glass tankfilled with glycerine, a webcam-based vision system and a dedicatedimage postprocessing tool able to estimate the positionand the terminal velocity of any particle falling in the tank;3) performing a calibration procedure to accurately estimate theuncertainty on particle velocity; and 4) comparing the experimentalresults with estimations obtained by some particle falloutmodels available in literature. Our results show that there is a goodagreement between experimental terminal velocities and thoseobtained applying a model which includes information on particleshape. The proposed methodology allows us to investigate how theparticle shape affects the sedimentation processes. Since the latteris strategic to improve the accuracy on modeling ash fallout, thiswork will contribute to reduce risks to aviations during explosiveeruptions.