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  • 1
    Publication Date: 2021-01-19
    Description: Multiparametric observations integrate signals from different techniques into a unified time and space frame, and are key in understanding and monitoring the evolution of volcanic systems and eruptive activity. Mafic explosive eruptions, with a relatively high frequency of occurrence and low intensity, allow for detailed multiparametric observations at a relatively close distance. Typically, pyroclast ejection in these eruptions is not steady, but is characterized by the occurrence of ejection pulses, linked to pressure release events and featuring a characteristic nonlinear decay of pyroclasts exit velocity. Pulse frequency, duration, and exit velocity define the dominant eruptive style, function of the volume and pressure of the released gas, conduit size, and magma rheological-mechanical properties. No important differences in pressure and velocity divide eruptions with different magnitude and style. Ejection pulses influence the geophysical signature, plume development, and the emplacement of ballistic volcanic projectiles at eruptions from Strombolian to Vulcanian styles.
    Description: Published
    Description: 379-411
    Description: 4V. Processi pre-eruttivi
    Description: 5V. Processi eruttivi e post-eruttivi
    Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio
    Keywords: Mafic eruption, Multiparametric monitoring, Eruption imaging, Volcano acoustic, Strombolian, Plume, Vent, Ballistic ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 2
    Publication Date: 2021-06-25
    Description: In a Strombolian volcanic eruption, bursting of a pressurized gas pocket produces and accelerates a mixture of gas and pyroclasts along a conduit and out of a vent. While mixture ejection at the vent is the subject of direct geophysical measurements, and a key to eruption understanding, the dynamics of how the mixture moves in the conduit are not observable and only partly understood. Here, we use analog, transparent shock tube experiments to study the dynamics of gas and particles under fast gas decompression in a vertical tube. Maximum particle exit velocity increases linearly with increasing energy (pressure times volume) of the pressurized gas, and, subordinately, with decreasing particle size and depth in the tube. Particles, initially at rest, are at first accelerated and dispersed in the conduit by the expanding gas. When the gas decelerates or even reverts its motion due to pressure changes in the tube, the particles, moving under their inertia, are then decelerated by the gas drag. Deceleration lasts longer for lower initial gas energy and for deeper particle starting position. Experiments and eruptions share two key vent ejection dynamics: 1) particles exit the vent already decelerating, and 2) the exit velocity of the particles decays over time following the same non-linear law. Friction with slower, or even back-flowing gas likely causes pyroclast deceleration in volcanic conduits during Strombolian explosions. Pyroclast deceleration, in turn, affects their exit velocity at the vent, as well as current estimates of the source depth of the explosions.
    Description: Published
    Description: e2019JB019182
    Description: 5V. Processi eruttivi e post-eruttivi
    Description: JCR Journal
    Keywords: Strombolian explosion ; volcanic conduit ; shock tube ; pyroclast ejection ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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