UNDERSTANDING ERUPTIVE DYNAMICS, PLUME DISPERSAL AND PARTICLE TRANSPORT FOR RISK ASSESSMENT IN PAROXYSMAL MAFIC ERUPTIONS

Paroxysmal activity at open vent volcanoes is a significant source of hazard as it occurs with limited and short-term precursory activity and has a severe impact both on proximal and distal regions because of tephra fallout and ash dispersion. Characterization of eruptive dynamics is therefore fundamental to reducing the risk associated with these eruptions. This thesis presents a study of several lava-fountain episodes at Etna that occurred between 2021 and 2024. Its aim is to improve our understanding of eruptive dynamics and better characterize key eruptive parameters used in monitoring operations for modelling tephra dispersal (Eruptive Source Parameters - ESP). The study therefore focused on summit-crater activity, with particular attention to the South-East Crater (SEC), which has been the most active in recent decades. A detailed investigation based on thermal-camera footage led to the proposal of a new low-cost methodology for real-time monitoring. The method is economical because it uses video from the thermal-camera system already installed within the INGV-OE monitoring network. Also have low computational costs because it processes RGB .png frames that are converted to grayscale using a simple function. The proposed method made it possible to detail the dynamics that lead up to fountain events and to identify the different phases of Etna’s paroxysmal episodes. Beyond its operational application, the method is useful retrospectively: it enables a more accurate estimate of the total eruption duration and can therefore refine time-dependent eruptive parameters (e.g., MER). These data also revealed multi-vent activity and exposed previously “hidden” dynamics of the shallow feeding system, showing alternating higher-intensity phases among the vents involved. Detailed studies were also performed on the pyroclastic material emitted during these fountain events. Because proximal sampling is extremely difficult (due to high hazard during eruptions, inaccessibility of some areas, and ephemerality of the deposits), the proximal fallout from Feb-Apr 2021 eruptive sequence, buried by snow layers, provided a unique opportunity. This study improved our understanding of the particle grain-size distribution at the source and allowed quantification of the error on the TGSD (Total Grain-Size Distribution - an input parameter for operational ash-dispersion models) when proximal tephra is not considered. Finally, through morphological and textural analysis of the pyroclasts from the fountain activity of 1 December 2023, and from study of the eruptive dynamics displayed by that eruption, it was possible to deepen understanding of pyroclastic transport and depositional mechanisms. The results show how the complex eruptive dynamics that develop during eruptions can alter the relative proportions of components within the total deposit. Such changes can significantly affect interpretations of conduit dynamics and lead to imprecise estimates of eruptive source parameters, such as magma ascent velocities and magma residence times within the conduit.