Article

Looking inside the Panarea Island (Aeolian Archipelago, Italy) by gravity and magnetic data

Annals of Geophysics 01/2009;
Source: DOAJ

ABSTRACT In this paper we show and discuss the results of gravity and magnetic surveys of Panarea Island and its archipelago. The most recent volcanic manifestation occurred in November 2002 with a shallow submarine gas eruption between the islets of Dattilo, Panarelli, Lisca Bianca, Bottaro and Lisca Nera. Currently, the activity of Panarea is monitored through a multidisciplinary study under the umbrella of the Italian Department of Civil Protection with the goal of defining the hazard of this area. With this aim, in May 2006 the first gravity and magnetic surveys of Panarea Island and its archipelago were performed. The offshore magnetic data were obtained using a marine magnetometer, a Geometrics G880, from the Istituto Idrografico dell Marina (IIM). Onshore and offshore magnetic data were integrated into an unique dataset for complete magnetic coverage of the study area. By using two micro-gravimeters (LaCoste & Romberg), gravity data were collected along tracks every 250 meters. The gravity dataset was processed using the standard method. A Bouguer reduction was applied to the free-air gravity dataset using a detailed digital elevation model of the island and the neighbouring sea after evaluation of the optimal Bouguer density to reduce the topographic effect. The result is a Bouguer anomaly map that shows lateral variations in density distribution and the relationships between the shallow volcanic/crustal features and tectonic lineaments. This evidence is also highlighted by the magnetic pattern, which suggests the importance of the youngest volcanic deposits with respect to the magnetic features of the island.

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    ABSTRACT: Panarea and surrounding Islets form a volcanic edifice, that is part of the Eastern sector of the Aeolian Arc, Southern Tyrrhenian Sea. It is now considered inactive, since last documented activity is 20 Ka old. However, on 2002-11-03, gas started to flow violently from the seafloor in an area E of the Island, mainly along NE and NW structural lineaments, and lasting up to 2003-2004 with a consistent flux, orders of magnitude larger that ’steady-state’ fumarolic activity documented there in historical times. On the same period a strong effusive activity of Stromboli (10 NM to NNE) was present. Since then, several investigations have been conducted at sea and on land, with the aim of focusing on the problem of effusive activity at sea, mainly in the light of volcanic surveillance and risk. Among these investigations, some of which have been repeated over years, we present and discuss some data and results from: (a)visual inspection and sampling by divers and ROV, (b)GPS networks and mapping by multibeam and LIDAR, (c) oceanographical measurements by current meters and CTD, and water flux and dynamics measurements, (d)magnetic and gravimetric surveys, (e) multichannel reflection Seismic with OBS and land station networks. Data were used for compilation of high resolution bathymetric, magnetic and gravimetric maps, including the emerged and submerged portions of the edifice.
    Marine Research at CNR, DTA/06-2011 edited by Brugnoli E., Cavarretta G., Mazzola S., Trincardi F., Ravaioli M., Santoleri R., 06/2011: pages 1468-1486; Consiglio Nazionale delle Ricerche., ISBN: ISSN 2239-5172
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    ABSTRACT: The November 2002 submarine gas blast at Panarea Island (Sicily, Southern Italy) was an unexpected reactivation event able to locally affect this hydrothermal-magmatic system whose the youngest eruptive products were dated at 20,000 ± 2,000 years BP. The presence of magmatic gases (SO2 and HF) in the fumarolic gas discharges after the violent exhalative event was indicative of a magmatic input that temporary displaced the hydrothermal system. A few months later these acidic gases were indeed not detected in any of the studied fumaroles. Nevertheless, new geochemical data obtained by periodical sampling up to June 2013 suggest that the chemical-physical conditions of the hydrothermal-magmatic system at Panarea were not completely restored with respect to the geochemical data obtained in the early nineties. Thus, the 2002 gas burst has unequivocally caused a permanent modification to the fluid circulation system feeding the submarine fumaroles. In addition, strong compositional differences were observed by the 46 gases collected in 2012-2013 from submarine fumaroles located in different sites of the studied area, allowing to distinguish three different groups of fumaroles: A) H2- and CO-rich gases, which also show relatively low Ar concentrations, B) H2S-rich gases, having variable CO/CH4 ratios, and C) Ar-rich gases, having relatively low H2 concentrations. Gases from group A are distributed along NW- and NE-trending fault systems, whereas those of group B and C discharge at increasing distance from the intersection of the two fault systems, indicating a spatial and compositional control by the local tectonic setting. The H2/CO ratios of group A and B gases are significantly lower than those measured prior 2012. This would imply an increase of gas pressure at depth, possibly caused to continuous addition of gas and energy from the magmatic source to the hydrothermal reservoir. Continuation of this process may lead to the occurrence of gas burst events in the next future, a hypothesis that is supported by the strong ongoing degassing activity at the surface notwithstanding a decrease of temperatures at depth. A geochemical, seismological and ground deformation monitoring of the Panarea submarine fumarolic field is highly recommended to obtain precursory signals of new strong degassing phenomena.
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