The analysis of the influence of pumice shape on its terminal velocity

Pumice particles represent the basic “ingredient” of many large explosive eruptions and form as a result of magma fragmentation inside the conduit. At the onset of eruption, fragmental pumices are expelled at high velocity from the crater by the overpressure of gas liberated on explosion. The resulting multiphase flow is forced through atmosphere by a variety of transportation mechanisms and pumices eventually decouple from the gas flow, settling down to form pyroclastic deposits. Here we propose new experimental data of terminal velocity together with a quantitative shape analysis of a wide range of pumice particles. The resulting model allows predicting the terminal velocity of pumice by means of easily measured particle characteristics, with an average error of 12%, which compares favourably with previous models.