Giacomo Ulivieri

Effusive to explosive transition during the 2003 eruption of Stromboli volcano

The persistent explosive activity of Stromboli volcano (Italy) ceased in December 2002 and correlated with the onset of a seven-month-long effusive eruption on the volcano flank from new vents that opened just below the summit craters. We intensively monitored this effusive event, collecting and interpreting, in real time, an extensive multiparametric geophysical data set. The resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical Strombolian activity. We present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity. This insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity.

Seismic, acoustic, and thermal network monitors the 2003 eruption of Stromboli Volcano

The date 28 December 2002, heralded the onset of a 7-month-long effusive eruption at Stromboli volcano in Italy. The onset was accompanied on 30 December by a large landslide (Figure 1). This landslide produced a tsunami that damaged the villages on Stromboli and affected coastal zones around the southern Tyrrhenian Sea [Pino et al., 2004]. Following the landslide, the eruption was mostly characterized by effusive activity with lava flows extending from vents between 500 and 650 m above sea level. Simultaneously, Strombolis typical explosive activity died out, with no explosions from the summit craters during the initial months of the eruption. However, a major explosive event on 5 April 2003 caused considerable alarm.

Tracking Pyroclastic Flows at Soufrière Hills Volcano

Explosive volcanic eruptions typically show a huge column of ash and debris ejected into the stratosphere, crackling with lightning. Yet equally hazardous are the fast moving avalanches of hot gas and rock that can rush down the volcanos flanks at speeds approaching 280 kilometers per hour. Called pyroclastic flows, these surges can reach temperatures of 400°C. Fast currents and hot temperatures can quickly overwhelm communities living in the shadow of volcanoes, such as what happened to Pompeii and Herculaneum after the 79 C.E. eruption of Italys Mount Vesuvius or to Saint-Pierre after Martiniques Mount Pelee erupted in 1902.

Infrasonic evidences for branched conduit dynamics at Mt. Etna volcano, Italy

An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union.

Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption

Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

Seismic Tomography Experiment at Italy's Stromboli Volcano

Stromboli Island, located in the southern Tyrrhenian Sea, is the emerged part (about 900 meters above sea level) of an approximately 3-kilometer-high stratovolcano. Its persistent Strombolian activity, documented for more than 2000 years, is sometimes interrupted by lava effusions or major explosions. Despite the number of recently published geophysical studies aimed at clarifying the volcanos eruption dynamics, the spatial extent and geometrical characteristics of its plumbing system remain poorly understood. In fact, knowledge of the inner structure and the zones of magma storage is limited to the upper few hundred meters of the volcanic edifice [Chouet et al., 2003; Mattia et al., 2004], and P and S wave velocity models are available only in restricted areas [Petrosino et al., 2002].

Tracking dynamics of magma migration in open-conduit systems

Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long-period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the magma column in response to an increased magma input rate. During the 2014 flank eruption of Stromboli, this magma input preceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial magma reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial magma recharge within an open-conduit system and to track magma drainage during the effusive crisis, with a great impact on hazard assessment.

Forecasting Effusive Dynamics and Decompression Rates by Magmastatic Model at Open-vent Volcanoes

Effusive eruptions at open-conduit volcanoes are interpreted as reactions to a disequilibrium induced by the increase in magma supply. By comparing four of the most recent effusive eruptions at Stromboli volcano (Italy), we show how the volumes of lava discharged during each eruption are linearly correlated to the topographic positions of the effusive vents. This correlation cannot be explained by an excess of pressure within a deep magma chamber and raises questions about the actual contributions of deep magma dynamics. We derive a general model based on the discharge of a shallow reservoir and the magmastatic crustal load above the vent, to explain the linear link. In addition, we show how the drastic transition from effusive to violent explosions can be related to different decompression rates. We suggest that a gravity-driven model can shed light on similar cases of lateral effusive eruptions in other volcanic systems and can provide evidence of the roles of slow decompression rates in triggering violent paroxysmal explosive eruptions, which occasionally punctuate the effusive phases at basaltic volcanoes.

Gas Flux Rate and Migration of the Magma Column

The 2002-2003 effusive eruption of Stromboli volcano represents an excellent opportunity to investigate the transition from effusive to explosive activity at an open-conduit basaltic system, when activity migrated from effusive vents, at the base of the craters, to summit explosions. The transition is investigated here through the analysis of very long period seismicity, delay times between infrasonic and thermal onsets of explosions, and SO2 flux recorded during a 1-year period. The synergy of the multiple geophysical observations points to a magma-driven migration of the magma column. Here the increased magma supply at the eruption onset lead to opening of effusive fissures, which draining the magma in the shallow conduit caused the decrease of the magma level. The decrease of the magma supply at the end of the effusion lead to sealing of effusive fissures, upraise of the magma level within the conduit, and reestablishment of explosive activity from the summit vents.