Luciano Giannini

1980–1990: Ten years of geochemical investigation at Phlegrean Fields (Italy)

Abstract A systematic geochemical investigation on the thermal manifestations of the volcanic area of Phlegrean Fields started in 1980, with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements, termed as “bradyseismic”, which frequently interested this area. The attention was initially given to the fumaroles and the boiling pools of Solfatara and Pisciarelli, then subsequently extended to thermal springs, dug wells, and crater lakes. Analytical data pertaining to a period preceding the last crisis of 1982–1984 were then available, as well as other data collected during the previous crisis of 1970; a comprehensive picture of the variations observed before, during and after the acceleration of vertical movement has been drawn. According to the results obtained, the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic. The whole area appears now in a quiet stage, and no further perturbation is expected without previous significant tectonic activity; chemical precursors appear suitable for an early detection of changes occurring at depth, to forecast possible consequences to be expected in the surface environment.

Composition of hydrothermal fluids during the bradyseismic crisis which commenced at Phlegraean Fields in 1982

A systematic geochemical surveillance on the fumaroles of Solfatara and the boiling pools of Pisciarelli was carried out by discontinuous monitoring of the chemical composition of the emitted fluids during the Phlegraean Fields bradyseismic crisis which has begun in 1982. The fluids are considered to be produced by the ebullition of shallow aquifers receiving a convective gaseous inflow from the underlying magma chamber.Increased water vapor concentrations at a constant temperature of about 155 °C throughout the investigated period, along with the occurrence of ground deformations and seismic phenomena, are interpreted as resulting from an increased heat supply to the boiling water bodies.Dissolution processes and reactions with the confining rocks can alter the chemical composition of fluids escaping from magma to a large extent. Therefore it does not appear correct to consider the absolute values of any chemical constituent for geochemical surveillance without taking this modifying factor into account. Acid gases will be preferably absorbed by the above mentioned aquifers, while other species like H2, N2, O2, CH4, will instead increase their relative concentrations. Because of this, water vapour concentrations and the ratios H2S/CO2 and H2/CH4 in surface thermal manifestations appear to reflect better the varying extent of the observed phenomenon.On the basis of these parameters, and of both the upheaval rate and the intensity of seismic events, maximum values in the convective input of magmatic origin are estimated to have occurred at the beginning of the crisis and in September–October 1983.As long as water bodies at shallow depth are able to buffer the convective flow both thermally and chemically, no important volcanic activity can develop. When the absorbing capacity of these aquifers is exhausted, the increasing temperature and the changing characteristics of fluids towards a magmatic composition will indicate a higher probability of eruptive phenomena.

Volatile organic compounds (VOCs) in air from Nisyros Island (Dodecanese Archipelago, Greece): Natural versus anthropogenic sources

This study presents the chemical composition of VOCs in air and gas discharges collected at Nisyros Island (Dodecanese Archipelago, Greece). The main goals are i) to discriminate between natural and anthropogenic VOC sources and ii) to evaluate their impact on local air quality. Up to 63 different VOCs were recognized and quantitatively determined in 6 fumaroles and 19 air samples collected in the Lakki caldera, where fumarolic emissions are located, and the outer ring of the island, including the Mandraki village and the main harbor. Air samples from the crater area show significant concentrations of alkanes, alkenes, cyclic, aromatics, and S- and O-bearing heterocycles directly deriving from the hydrothermal system, as well as secondary O-bearing compounds from oxidation of primary VOCs. At Mandraki village, C6H6/Σ(methylated aromatics) and Σ(linear)/Σ(branched) alkanes ratios <1 allow to distinguish an anthropogenic source related to emissions from outlet pipes of touristic and private boats and buses.

Seafloor doming driven by degassing processes unveils sprouting volcanism in coastal areas

We report evidences of active seabed doming and gas discharge few kilometers offshore from the Naples harbor (Italy). Pockmarks, mounds, and craters characterize the seabed. These morphologies represent the top of shallow crustal structures including pagodas, faults and folds affecting the present-day seabed. They record upraise, pressurization, and release of He and CO2 from mantle melts and decarbonation reactions of crustal rocks. These gases are likely similar to those that feed the hydrothermal systems of the Ischia, Campi Flegrei and Somma-Vesuvius active volcanoes, suggesting the occurrence of a mantle source variously mixed to crustal fluids beneath the Gulf of Naples. The seafloor swelling and breaching by gas upraising and pressurization processes require overpressures in the order of 2–3 MPa. Seabed doming, faulting, and gas discharge are manifestations of non-volcanic unrests potentially preluding submarine eruptions and/or hydrothermal explosions.

The fumaroles of Vulcano (Italy): differences in chemical compositions produced by the surface environment

Abstract The results of investigations carried out on volcanic gases during the Field Workshop held at Vulcano in September 1982 are reported. A brief description is given of the differentiated sampling and analytical procedures used for acid, condensable and non-condensable gases. The fumaroles at the crater are characterized by different temperatures but substantially uniform composition, indicating a common genetic process; in addition to gaseous species peculiar to a magmatic environment, waters of marine origin appear to be recycled into the feeding paths of these manifestations. The composition of the bubbling gases at the beach and in mud pools is considered to be the result of the flow of gaseous species of deep origin through shallow and surface aquifers; acid gases are preferentially absorbed and the concentrations of slightly soluble species, such as H 2 , N 2 , O 2 and CH 4 , are considerably enhanced.

Environmental Pollution Due to Natural Factors: A Case Study in A Volcanic Area (Vulcano Island, Italy)

Abstract A major influence on the environment of active volcanic areas is expected from continuous input of chemical species pertaining to fumarolic activities occurring during inter-eruptive intervals. The systematic investigations carried out during thirteen years in the island of Vulcano (Italy) showed also substantial contributions to phreatic waters and soils of minor constituents and trace metals from volcanic rocks with no negligible influence on growing crops. Greater extents of these phenomena have been observed for products of hydromagmatic volcanic activity or of long-lasting weathering processes.