Multiparametric Approach in Investigating Volcano-Hydrothermal Systems: the Case Study of Vulcano (Aeolian Islands, Italy)

Abstract

Seismic activity, ground deformation, and soil and fumarole temperatures acquired during 2004-2007 at Vulcano (Aeolian Islands) are analysed and the time relations among the different time series are discussed. Changes in temperature of fumarolic gases took place during four ''anomalous'' periods () at the same time as an increasing number of volcano-seismic events. In particular, the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440°C and from 20 to 90°C, respectively. The maximum daily number of volcano-seismic events was 57, reached during the second anomalous period. This seismicity, characterised by focal depth generally lower than 1 km below sea level (b.s.l.) and composed of different kinds of events associated to both resonance and shear failure processes, is related to the shallow dynamics of the hydrothermal system. During the analysed period, very few volcano-tectonic earthquakes took place and tilt recordings showed no sharp or important changes. In light of such observations, the increases in both temperature and volcano-seismic events number were associated to increases in the release of gas from a deep and stable magma body, without magma intrusions within the shallow hydrothermal system. Indeed, a greater release of gas from depth leads to increased fluid circulation, that can promote increases in volcano-seismic events number by both fracturing processes and resonance and vibration in cracks and conduits. The different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body. Finally, all the observed variations, together with the changing temporal distribution of the different seismic event kinds, suggest that the hydrothermal system at Vulcano can be considered unsteady and dynamic.

Heat flux-based strategies for the thermal monitoring of sub-fumarolic areas: Examples from Vulcano and La Soufrière de Guadeloupe

“…In order to get a better overview of the fumarolic activity, we also used for comparison data from other instruments of the volcano perma nent network ( Fig. 3a): i) a rain gauge providing hourly measurements, located in open air at the harbor, about 1000 m from the PN tempera ture station (database Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, courtesy of Paolo Madonia); ii) a seismic station maintained by the INGV from which the daily number of seismic events can be counted (Cannata et al, 2012); iii) a UV scanning DOAS MARK1 allowing daily estimations of the total SO 2 flux from the volcano (see an extended description in Vita et al, 2012); and iv) a WEST Systems CO 2 flux meter with an automated accumulation chamber providing daily estimate of the diffuse CO 2 flux at the summit area (see an extend ed description in Inguaggiato et al, 2012b) coupled with an open air thermometer. Note that the geochemical data were not corrected from the atmospheric conditions that may influence the observations (Viveiros et al, 2008), and that the reported seismic data represent the daily number of events and short lived interruptions may have caused some values underestimations.…”

Hydrothermal fluid flow disruptions evidenced by subsurface changes in heat transfer modality: The La Fossa cone of Vulcano (Italy) case study

“…Small perturbations temporarily increasing the pore pressure can modify the effective normal stress and trigger seismicity. This phenomenon and other fracturing processes (due to alteration of rock to secondary minerals by reducing the shear stress required to initiate fracturing and/or increases in temperatures in the rock and consequent rock fracturing) are also able to enhance the rock's vertical permeability, thus favoring the rise of fluids (Cannata et al, 2012, and references therein).…”

“…We compared seismic data with our results, because seismic swarms suggest the disruption of the hydrothermal system, an increase of the permeability inside the edifice, and consequently an increase of hot fluids flow toward the surface (Cannata et al, 2012;Milluzzo et al, 2010).…”

“…At Vulcano, seismicity is associated with volcano-tectonic sources or is related to fluid dynamics within the hydrothermal system (Aubert et al, 2008;Cannata et al, 2012;Madonia et al, 2013). The first case is generally related to the north-northwest-south-southeast Tindari-Letojanni regional fault system dynamics and results in a few events per year, while the second comprises seismovolcanic events occurring in the hydrothermal system underlying La Fossa cone, from several hundred to thousands per year (Alparone et al, 2010;Milluzzo et al, 2010; see the Data Repository).…”

Analysis of Thermal Anomalies in Volcanic Areas Using Multiscale and Multitemporal Monitoring: Vulcano Island Test Case

“…During inter-eruptive periods, the thermal emissions by hydrothermal fluids, the emission of steam through the fumaroles and even the diffuse heat release from the ground are a significant part of the total energy released by the volcano. This slow and restless energy release is, in the long term, comparable to the seismic release of volcano-tectonic origin [6][7][8][9][10][11]. For many years, the amount of convective energy released on the surface of the Island of Vulcano has been estimated by direct samplings and measurements of the fumaroles of La Fossa cone [7,12], and the exhaling temperatures and the steam flows in some sample points have been measured.…”