Synergy of multiple geophysical approaches to unravel explosive eruption conduit and source dynamics - A case study from Stromboli

摘要

An effective approach to understanding the dynamics of explosive volcanic eruptions and the conduit systems that drive them is through synergy of multiple data sets.Three data sets that lend themselves to ease of integration are seismic,infrasonic and thermal.Although approaches involving these data have been used to record volcanological phenomena since 1862,1955 and 1965,respectively,their integrated use has only developed since 1999.When combined,these three data sets allow constraint of shallow system geometry and the dynamics of the explosive events that occur within that system.Using Stromboli volcano (Italy) as a case study,we review the complete range of geochemical and geophysical studies that can be applied.In doing so,we aim to show how integration of these diverse studies allows insights into a plumbing system and the dynamics of the eruptive activity that the system feeds.When combined at Stromboli,these data provide constraint of multiple system parameters including chamber depths,gas and magma fluxes,shallow system magma residence times,explosion source depths,and the rise/ejection velocities of ascending gas slugs and ejecta.In turn,these results allow various conduit and eruption dynamic models to be applied and tested.The persistent and repeated mildly explosive events that characterize Stromboli have been modeled in terms of the coalescence of gas within the magma to form large gas slugs that ascend the remaining portion of the conduit to burst at the free surface.Our integrated seismic,infrasonic and thermal data sets indicate that gas coalescence occurs at a depth of ~260 m,with a typical event frequency of ~9/h.Infrasonic and thermal data show the explosion source to be located 20-220 m below the vent.Thermal data give emission velocities for the ejected fragments of 8-20 m/s,which converts to gas jet velocities of 23-39 m/s.Tracking these parameters in space and time shows that,although eruptions at Stromboli can be grouped into two characteristic types (simple and complex-each of which characterizes a particular crater,NE and SW,respectively),events within each type show significant short-term variability.The system does,however,appear robust,maintaining its characteristic strombolian eruption style after significant effusive phases and more energetic explosive events.