IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3W_2D-P15

Date/Time: July 23 Poster

Magnetic signatures of volcanic unrest: learning from long-term data at Mt Etna,Stromboli and La Fournaise volcano
Rosalba Napoli1 , Jacques Zlotnicki2 , Gilda Currenti1 , Frederic Fauquet2 , Filippo Greco1 , Paul Yvetot2 ,Ciro Del Negro1
1Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania, Italy, 2 Observatoire de Physiquedu Globe de Clermont-Ferrand-CNRS, France
E-mail: napoli@ct.ingv.itThe long-term monitoring of the geomagnetic field at different volcanoes can give valuable information for improving
the understanding of the volcanic structures and the dynamics of eruptions. The modifications of the magnetic
properties of volcanic rocks as well as the hydrothermal activity can generate a wide variety of magnetic signals, as
piezomagnetic, thermomagnetic and electrokinetic effects. In addition, the local magnetic field changes are strongly
related to magma dynamics.
The characterization of these signals, which depends on the structural heterogeneity, the stress field, and thehydrothermal state of each volcanic edifice, is a key step for improving the detection of small magnetic signals andfor understanding the mechanisms that produce them.
During the last decades, geomagnetic observations have been intensively carried out at different volcanoes aroundthe world (Japan: Miyake-jima; Italy: Etna and Stromboli; France: La Fournaise Philippines: Taal), and significant
correlations between volcanic activity and changes in the local magnetic field have been observed. In particular, aseries of coherent observations on Etna, Stromboli and La Fournaise volcanoes have led to significant advances inthe systematic study of the amplitude and the origin of measurable volcanomagnetic effects. The spatio-temporal
evolution of the signals observed at Etna and Stromboli during the latest eruptions (2003, 2007, 2008 and 2011)
are of piezomagnetic origin. They allowed to model the magmatic intrusions at shallow depth and the stress field
progress within the volcanoes. Volcanomagnetic signals recorded at La Fournaise, between 1986 and 2004, havecontributed to improve the knowledge of the eruptive behavior of this volcano. Signals up to a tens of nanoTeslas
were observed in the last weeks to a few hours before effusive activity. The signals were mainly attributed toelectrokinetic effect. The magnetic field observations highlight the usefulness of magnetic monitoring networks ascomplementary techniques to traditional permanent geophysical arrays.
The long and high-quality geomagnetic sequences recorded during the last two decades at Etna, Stromboli and La
Fournaise volcanoes are an essential database for a detail comparison between these volcanoes. Their specificmagnetic signatures will be highlighted in accordance to the different types of eruptive activity. The expected results
should contribute to the evaluation in real time of the typology and the level of activity of the volcanoes. It could
help to estimate pre-alarm/alarm thresholds relevant for civil protection decisions.

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