HR: 0830h
AN: V51F-0352    [PDF]
TI: Geochemical Monitoring of Vesuvius Aquifer: temporal variations in the chemical and isotope composition of water and dissolved gases
AU: * Federico, C
EM: federico@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, Ita 90146 Italy
AU: Aiuppa, A
EM: aiuppa@pa.ingv.it
AF: Dipartimento CFTA, Universit… di Palermo, Via Archirafi 36, Palermo, Ita 90123 Italy
AU: Favara, R
EM: favara@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, Ita 90146 Italy
AU: Gurrieri, S
EM: peppo@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, Ita 90146 Italy
AU: Madonia, P
EM: madonia@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, Ita 90146 Italy
AU: Rizzo, A
EM: andrearizzo@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, Ita 90146 Italy
AB: The cold aquifer hosted in the volcanic sequence of Mt Vesuvius locally receives the input of fluids upraising from the deep hydrothermal system, mostly in correspondence of tectonic lineaments, dissecting both the volcanic edifice and the sedimentary basement (Bianco et al, 1998, Ventura et al., 1999). In particular, the southern flank of the volcano is affected by an intense CO2 degassing, associated to a weak thermal anomaly. Helium isotopes furnish further important clues about the mapping of volcanic degassing, revealing an input of magmatic fluids even on the northern flank of the volcano (Federico et al., 2002). Since 1998, a set of drilled wells (9) and springs (3) are monthly sampled and analysed for their chemical and isotope composition. Time series indicate a fair constant composition for the whole aquifer. Temperature, pH, alkalinity and dissolved CO2 are also rather stable, mostly in deeper wells (piezometric level deeper than 100 m). Shallower water bodies present a stronger temporal variability, caused by seasonal and anthropogenic effects. The present state of dormancy on Mt. Vesuvius offers a good opportunity of measuring background values for most parameters, useful to eventually evaluate a progressive unrest of the volcano. Actually, significant variations in water chemistry were observed in correspondence of the seismic event occurred in October 1999, mostly in a low flux spring, located on the northern flank of Vesuvius. In this site, a strong decrease of pH (0.1 pH unit) and redox potential (from +200 to -150 mV), together with an increase of both dissolved CO2 and 3He/4He ratio, were observed. These variations were attributed to a seismically-induced input of deep He and CO2 to the small water body feeding the spring. Conversely, in the main aquifer, the stress-field produced by the earthquake modified the relationship between superposed water bodies, with the final effect of a change in the water chemical composition. Almost all monitored sites showed a salinity decrease before the October 1999 earthquake, followed by a gradual reestablishment of pre-seismic conditions. In the last period, synchronous variations in the dissolved helium isotope ratios were observed, probably related to either a variable contribution of crustal gases or variable magmatic degassing.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting