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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS007 Oral Presentation 1960<br />

Large magnetic changes at Etna Volcano (Italy) observed before and<br />

during the 2006 eruption<br />

Dr. Rosalba Napoli<br />

Istituto Nazionale di Geofisica e Vulcanologia Istituto Nazionale di Geofisica e Vulcanologia<br />

Gilda Currenti, Ciro Del Negro, Davide Giudice<br />

The latest eruption of Mt Etna, occurred from July to December 2006, was characterized by episodic<br />

eruptive activity involving a number of explosive and effusive vents in the summit craters. From the<br />

beginning of 2006 significant geomagnetic changes were recorded by the permanent magnetic network<br />

of Mt Etna. The present network consists of 6 scalar magnetometers and 3 magnetic gradiometers.<br />

Stations are located at elevations ranging between 1700 and 3000 m a.s.l. along a North-South profile<br />

crossing the summit craters. All magnetic stations are equipped with Overhauser effect magnetometer<br />

(0.01 nT sensitivity) and synchronously sample the Earths magnetic field every 5 seconds. Between<br />

January and July 2006, after differential magnetic fields were filtered from the seasonal thermal noise<br />

by Independent Component Analysis, a slow and continuous decrease in the magnetic field total<br />

intensity greater than 5 nT was observed at almost all the sites of the southern flank of Mt Etna.<br />

Magnetic data indicate that changes in the magnetization within the volcano are caused by<br />

thermomagnetic effects. The location of the demagnetized region, which is supposed to be the region<br />

heated by high-temperature liquids and gases originating from magma, was estimated by the spatial<br />

distribution of the variation rate. At the beginning of November 2006 a large and sharp decrease of the<br />

geomagnetic field was detected at the station of MFS. The anomaly reached the maximum amplitude of<br />

more than 150 nT in about two months with a variation rate of about 10 nT/day. At the end of January<br />

2007 the phenomenon was still in progress, even if the variation rate drastically decreased to 0.5<br />

nT/week. The large anomaly could be of thermomagnetic origin engendered by lava flows emitted by an<br />

effusive vent on 6 November, which threatened station and stopped at about 30 m from the magnetic<br />

sensor.<br />

Keywords: geomagnetic changes, mt etna

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