Showing papers by "Giovanni Chiodini published in 2011"

Temperature and pressure gas geoindicators at the Solfatara fumaroles (Campi Flegrei)

Abstract: Long time series of fluid pressure and temperature within a hydrothermal system feeding the Solfatara fumaroles are investigated here, on the basis of the chemical equilibria within the CO2–H2O–H2–CO gas system. The Pisciarelli fumarole external to Solfatara crater shows an annual cycle of CO contents that indicates the occurrence of shallow secondary processes that mask the deep signals. In contrast, the Bocca Grande and Bocca Nova fumaroles located inside Solfatara crater do not show evidence of secondary processes, and their compositional variations are linked to the temperature–pressure changes within the hydrothermal system. The agreement between geochemical signals and the ground movements of the area (bradyseismic phenomena) suggests a direct relationship between the pressurization process and the ground uplift. Since 2007, the gas geoindicators have indicated pressurization of the system, which is most probably caused by the arrival of deep gases with high CO2 contents in the shallow parts of the hydrothermal system. This pressurization process causes critical conditions in the hydrothermal system, as highlighted by the increase in the fumarole temperature, the opening of new vents, and the localized seismic activity. If the pressurization process continues with time, it is not possible to rule out the occurrence of phreatic explosions.

First 13C/12C isotopic characterisation of volcanic plume CO2

Abstract: We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.

Long time-series of chemical and isotopic compositions of Vesuvius fumaroles: evidence for deep and shallow processes

Abstract: Long time-series of chemical and isotopic compositions of Vesuvius fumaroles were acquired in the framework of the volcanic surveillance in the 1998-2010 period. These allow the identification of processes that occur at shallow levels in the hydrothermal system, and variations that are induced by deep changes in volcanic activity. Partial condensation processes of fumarolic water under near-discharge conditions can explain the annual 18O and deuterium variabilities that are observed at Vesuvius fumaroles. Significant variations in the chemical compositions of fumaroles occurred over the 1999-2002 period, which accompanied the seismic crisis of autumn 1999, when Vesuvius was affected by the most energetic earthquakes of its last quiescence period. A continuous increase in the relative concentrations of CO2 and He and a general decrease in the CH4 concentrations are interpreted as the consequence of an increment in the relative amount of magmatic fluids in the hydrothermal system. Gas equilibria support this hypothesis, showing a PCO2 peak that culminated in 2002, increasing from values of ~40 bar in 1998 to ~55-60 bar in 2001-2002. We propose that the seismic crisis of 1999 marked the arrival of the magmatic fluids into the hydrothermal system, which caused the observed geochemical variations that started in 1999 and culminated in 2002.

High Resolution Monitoring of Campi Flegrei (Naples, Italy) by exploiting TerraSAR-X data: An Application to Solfatara Crater

Abstract: Geodetic monitoring of Campi Flegrei caldera, west of Naples (Italy), is carried out through integrated ground based networks and space-borne Differential InSAR (DInSAR) techniques, exploiting the SAR sensors onboard ERS1-2 (till the end of their lifetime) and ENVISAT satellites. Unfortunately, C-band sensors give no information when dealing with very low deformation rates and very small deforming areas. To overcome these problems, we decided to use TerraSAR-X from DLR, a high resolution SAR sensor operating in the X-band, starting in December 2009. TerraSAR-X Spotlight scenes covering the main part of the Campi Flegrei caldera and centred on the Solfatara crater were used for a DInSAR analysis, using DLR’s InSAR software. Starting from this period, many field surveys highlighted a strong fumarolic activity in the Solfatara - Pisciarelli area [1], so geodetic and geochemical observations were strongly increased. Furthermore, the growing stack of High-Resolution Spotlight TerraSAR-X data processed using the Small Baseline Subset Algorithm (SBAS) as described by Berardino at al. [2], allowed getting information for a bigger area and data from ground based networks could be integrated. First results of the SBAS processing and the combination of different observation techniques are presented.

Analysis of temperature time series from thermal IR continuous monitoring network (TIIMNet) at Campi Flegrei Caldera in the period 2004-2011

Abstract: The TIIMNet stations. The Thermal Infrared Monitoring Network (TIIMNet) is planned for continuous, long-term volcanological monitoring by acquiring daily infrared images (LWIR 8-14 ?m) of fumaroles fields in the Neapolitan volcanic areas monitored by INGV-Osservatorio Vesuviano. The network is made up of three stations located, respectively, at Vesuvius crater, inside the Solfatara crater and at Pisciarelli (Fig. 1; Vilardo et al., 2008). The IR cameras used at Solfatara and Pisciarelli are NEC Thermo Tracer TS7302 with focal plane array (FPA) uncooled microbolometer measuring systems (320x240 pixel). The first one, operative since July 2004, acquires scenes of the SE inner slope of Solfatara at the intersection of two active, SW-NE and NW-SE main faults where are located the major fumaroles (Fig. 1a’) at an average distance of about 300 m from the IR camera. The IR camera at Pisciarelli, operative since October 2006, acquires scenes of the outer eastern flank of the Solfatara tuff-cone (average distance of fumaroles is about 130 m), corresponding to an area characterized by heavy water vapor and CO2 emissions (Fig. 1b’). Both IR cameras are inside a protective stainless steel housing, resistant to corrosive elements and with a shooting window of germanium glass, transparent to the thermal wavelengths; the cameras are connected to the Remote Monitoring Stations (RMS) which controls the shooting functionalities of IR sensors. The Control Unit, located at the surveillance center of INGVOsservatorio Vesuviano in Naples, communicates with the RMS through GSM frequency network and it allows to configure times and shooting parameters and to run the automatic uploading of the remotely acquired thermal images. The IR camera used at Vesuvius is FLIR ThermoVision A40 (FPA uncooled microbolometer, 320x240 pixel) which has been operating since July 2011 and acquires scenes of the SW inner slope of Vesuvius crater. The camera, which is inside the same protective housing used for NEC cameras, is connected to a new RMS (Fig. 2a) with new and improved functionalities and more flexibility in respect of the old RMS used at Solfatara and Pisciarelli. The new RMS can be programmed to perform IR shots at prefixed times, with temperature and humid-