The variability of the Strombolian activity
IPGP - Îlot Cuvier
Soutenances de thèses
Salle P07 Outremer
Dynamique des fluides géologiques (DFG)
Strombolian activity, characterised by series of small explosions at open-vent volcanoes, exists worldwide in various tectonic contexts. The variability of the Strombolian activity can be observed on a global scale and on the scale of a volcanic system. We performed two multidisciplinary studies to characterise the variability of the Strombolian activity. A thermo-infrasonic study at Erta’Ale (Ethiopia), Piton de la Fournaise (Re?union Island, France) and Yasur (Tanna Island, Vanuatu) allowed us to characterised the Strombolian activity as small and strong from numerous geophysical parameters. The thermo-infrasonic energy budget validated the existence of a sole mechanism of fragmentation for all Strombolian explosions. The Strombolian activity, often persistent, produces large volumes of gas that can interact with the atmosphere. These larges gas volumes are of the same order of magnitude, when averaged on a few centuries, than the gas volumes produced by larger volcanic eruptions, far less frequent, such as the Pinatubo eruption in 1991. Infrasonic, seismic and thermal measurements during two field campaigns at Yasur highlighted the coexistence of the progressive coalescence into the conduit and the massive coalescence in the reservoir that are responsible for the bubble formation. The massive coalescence exists, when the critical gas flux, above which the foam layer at the top of the reservoir becomes unstable, is exceeded. This critical gas flux allowed us to estimate the bubble diameter in the reservoir and gave consistent values compared to values obtained at other basaltic systems (Etna, Italy; Kilauea, USA; Erta’Ale, Ethiopia). Keywords: Strombolian; infrasounds; thermal; seismic; Yasur; Piton de la Fournaise.