[1] Total CO 2 output from fumaroles, soil gas, bubbling gas discharges and water dissolved gases discharged from the island, was estimated for Vulcano island, Italy. The CO 2 emission from fumaroles from the La Fossa summit crater was estimated from the SO 2 crater output, while CO 2 discharged through diffuse soil emission was quantified on the basis of 730 measurements of CO 2 fluxes from the soil of the island, performed by using the accumulation chamber method. The results indicate an overall output of ≅500 t day À1 of CO 2 from the island. The main contribution to the total CO 2 output comes from the summit area of the La Fossa cone (453 t day À1 ), with 362 t day À1 from crater fumaroles and 91 t day À1 from crater soil degassing. The release of CO 2 from peripheral areas is ≅20 t day À1 by soil degassing (Palizzi and Istmo areas mainly), an amount comparable to both the contribution of water dissolved CO 2 (6 t day À1 ), as well as to seawater bubbling CO 2 (4 t day À1 measured in the Istmo area). Presented data (September 2007) refer to a period of moderate solphataric activity, when the fumaroles temperature were 450°C and gas/water molar ratio of fumaroles was up to 0.16. The calculated total CO 2 emission allows the estimation of the mass release and related thermal energy from the volcanic-hydrothermal system.
International audienceSoil-temperature measurements can provide information on the distribution of degassing fissures, their relationship to the internal structure of the volcano, and the temporal evolution of the system. At Vulcano Island (Italy), heat flux from a <3 km-deep magma body drives a hydrothermal system which extends across the main Fossa crater. This heat flux is also associated with variable magmatic gas flow. A high-density map of soil-temperatures was made in 1996 at a constant depth of 30 cm on the central and southern inner flanks of the Fossa crater. These measurements extended over an area covering about 0.04 km2, across which the heat flux is predominantly associated with a shallow boiling aquifer. The map shows that hot zones relate to structures of higher permeability, mainly associated with a fissure system dating from the last eruptive cycle (1888–1890). From 1996 to January 2005, we studied the evolution of the heat flux for the high temperature part of the map, both by repeating our measurements as part of 14 visits, during which temperatures were measured at a constant depth, and using data from permanent stations which allowed soil-temperatures to be continuously measured for selected vertical profiles. These data allowed us to calculate the heat flux, and its variation, with good precision for values lower than about 100 W m−2, which is generally the case in the study area. Above 100 W m−2, although the heat flux value is underestimated, its variations are recorded with an error less than 10%. During the period 1996–2004, two increases in the thermal flux were recorded. The first one was related to the seismic crisis of November 1998 which opened existing or new fissures. The second, in November 2004, was probably due to magma migration, and was associated with minor seismic activity
Measurements of CO 2 flux from the ground were periodically carried out on the island of Vulcano (Aeolian Islands, Italy) between 1984 and 1994. Three high-flux areas were identified at the foot of the volcanic cone (La Fossa), either inside or very close to the main village. Effect of the choice of the sampling grid was evaluated. A different sampling grid resulted in similar distribution patterns, but with different CO 2 fluxes. Therefore, the absolute estimate of the total flux from the investigated area includes a large degree of uncertainty, but repeated measurements with permanent sampling sites are accurate and can detect small changes. No correlation of the flux with atmospheric parameters was found at sites with high fluxes. Some periods characterized by high CO 2 fluxes were observed, and a close correlation was found between the gas emissions from the ground and other geochemical and geophysical parameters such as temperature, chemical composition, steam, and SO 2 flux from fumaroles, seismic energy release, and ground deformations. The results show that major temporal variations of diffuse CO 2 flux are related to variations in volcanic activity.
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.
On Vulcano Island (Italy), many geochemical crises have occurred during the last 130 years of solfataric activity. The main crises occurred in 1978–1980, 1988–1991, 1996, 2004–2007, 2009–2010 and the ongoing 2021 anomalous degassing activity. These crises have been characterized by early signals of resuming degassing activity, measurable by the increase of volatiles and energy output emitted from the summit areas of the active cone, and particularly by increases of gas/water ratios in the fumarolic area at the summit. In any case, a direct rather than linear correspondence has been observed among the observed increase in the fluid output, seismic release and ground deformation, and is still a subject of study. We present here the results obtained by the long-term monitoring (over 13 years of observations) of three extensive parameters: the SO2 flux monitored in the volcanic plume, the soil CO2 flux and the local heat flux, monitored in the mild thermal anomaly located to the east of the high-temperature fumarole. The time variations of these parameters showed cyclicity in the volcanic degassing and a general increase in the trend in the last period. In particular, we focused on the changes in the mass and energy output registered in the period of June–December 2021, to offer in near-real-time the first evaluation of the level and duration of the actual exhalative crisis affecting Vulcano Island. In this last event, a clear change in degassing style was recorded for the volatiles emitted by the magma. For example, the flux of diffused CO2 from the soils reached the maximum never-before-recorded value of 34,000 g m−2 d−1 and the flux of SO2 of the plume emitted by the fumarolic field on the summit crater area reached values higher than 200 t d−1. The interpretation of the behavior of this volcanic system, resulting from the detailed analyses of these continuous monitoring data, will complete the framework of observations and help in defining and possibly forecasting the next evolution of the actual exhaling crisis.
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