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Mt. Etna Errupts Again. And Magnetometers are a Key Part of the Picture


Image courtesy of Alfio Amantia.
INGV Catania section.

Largely dormant since its last eruption in 2001, Sicily’s Mt. Etna roared to life again on October 27th, 2002, leaving hundreds homeless on a temporary basis. The event closed airports and caused residents in Catania, Italy’s second largest city to use umbrellas to protect themselves from flaming ash raining down from the mountain. The Italian government immediately issued a state of emergency in the region.

In the midst of this activity, a group of dedicated scientists from the Instituto Nazionale di Geofisica e Vulcanologia (INGV) has been extremely busy as well keeping up with the reams of data being recorded from magnetic instrumentation situated around the site. Group members, including Dr. Ciro Del Negro and Rosalba Napoli, will have more than enough work for the next several months analyzing results in search of an increased understanding of Mt. Etna’s behavior.

Automated Monitoring of Active Volcanoes

The INGV scientists will be examining data from a novel automated system for monitoring of active volcanoes. The Mag-Net system is set up to provide recording and analysis of magnetic data at large distances from Catania’s control centre.

Like most active volcanoes, Mt. Etna did not have a monitoring system until one was set up in the mid-90’s. Since then, the team has been steadily enhancing the system so that data acquisition is totally automated and operators can devote their entire attention to interpreting the data.

The system comprises a set of five stations on Mt. Etna with a sixth external reference station installed to the west of the main stations. This enables local magnetic transients related to the volcano to be isolated.

As shown in the image above, the network location is symmetrical with respect to the central craters to enable continuous measurements of the geomagnetic field along this section. The sites were chosen specially for their low, local magnetic gradient (less than 50 nT/m) and low local noise.

Magnetometer Implementation

The magnetometer system shown below is based on the GSM-90 EUROMAG (i.e. Overhauser Effect) magnetometers.

According to Dr. Del Negro, “We selected the GSM-90 Overhauser magnetometer, which is microprocessor based with full remote control capability. The results of measurements are made available in serial form for collection by data acquisition systems. Their characteristics turned out to be particularly suitable for continuous measurements in harsh environmental conditions such as we experience on Mt. Etna.”

Data Analysis and Modeling

INGV professionals receive data via mobile phone connections and can then start to analyze the data using modeling software. Data is analyzed for a variety of magnetic phenomena, including:

  • Thermomagnetic effects related to upwelling of magma.
  • Electrokinetic effects from pressure gradients. Gradients can generate electrofiltration currents that cause corresponding electrokinetic magnetic anomalies.
  • Piezomagnetic effects related to mechanical stresses in the vicinity of volcanoes. The redistribution of the stress field may modify not only the magnetization of rocks but also the network of interconnected pores.

Working toward Greater Understanding of Eruptions

Ultimately, the benefits of the integrated system are in providing real-time data and analytical techniques to assist in monitoring and forecasting of future eruptions.

With a wealth of new data from the latest eruption, the group should move a little closer to their ultimate goal – achieving substantial improvements in the knowledge of the shallow plumbing system (i.e. magmatic venting structure) at the Mt. Etna volcano, and consequently, investigation of any possible magnetic transients before and during eruptions.

Note: Interested readers can find more information about these effects and the magnetometer system in a research paper, entitled, “Automated system for monitoring of active volcanoes” by C. Del Negro, R. Napoli and A. Sicali in Bull. Volcanol (2002) 64: 94-99, copyright Springer-Verlag.

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Volcanomagnetic Signals Associated with the 2001 Flank Eruption of Mt. Etna (Italy)

Ciro Del Negro 1 and Gilda Currenti 1,2 Geophysical Res. Lett. 2002GLO15481, in print.

1 Istituto Nazionale DI Geofisica e Vulcanologia – Sezione DI Catania, Italy

2 Dipartimento Elettrico Elettronico e Sistemistico – Università degli Studi DI Catania, Italy

Abstract

Geomagnetic changes were observed during the 2001 flank eruption at Mt. Etna. After differential magnetic fields were filtered from the seasonal thermic noise by using temperature data, we recognized three stages in the total intensity changes related to different volcanic events: (a) rapid variation of 4 nT associated with July 12 seismic swarm recorded beneath the summit craters, (b) step-like variation of 7 nT occurring during the quick propagation of fractures in the south flank, which was followed by the offset of 2 nT before July 17 when the lava outpoured from fissures, and (c) quick variation of 3 nT coincident with July 19 eruptive fissures opening up in the Valle del Leone.

These observations are consistent with those calculated from volcanomagnetic models, in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth and by the thermal demagnetization at a rather shallow depth.

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Magnetic History of a Dyke on Mt. Etna, Italy

Ciro Del Negro 1 and Fabrizio Ferrucci 2 Geophysical J. Int (1998). 133, 451-458.

1 Istituto Internazionale DI Vulcanologia – CNR, 2 Piazza Roma, I-95123 Catania, Italy

2 Dipartimento Scienze della Terra, Università della Calabria, I-87036 Arcavacata DI Rende (CS), Italy

Summary

During the 1989 eruption of Mt. Etna, two fracture systems opened at the foot of its 3000 m high Southeast Crater and, trending ca. N45°E and N150°E, propagated quickly downslope to a distance of ca. 3 and 7 km, respectively. The north-eastern fracture fed a flank eruption, whereas the southeastern remained dry and offered contrasting volcanological and geophysical evidence of the presence of magma at a shallow depth.

During the opening of this non-eruptive fracture system, a differential magnetic network was set up on a short profile across its distant extremity. Initially, the magnetic field did not display any change along the profile between frequent surveys. However, repeated measurements at intervals of about 3 months for two years revealed the slow buildup of a 130 nT anomaly. The anomaly vanishes laterally within 0.2 km from the surface expression of the fracture system.

This exceptional set of observations constrains the location and time of cooling of a shallow dyke. The increase in magnetization of the dyke inferred by the rate of growth of the anomaly, leads to the interpretation that the dyke was emplaced near the end of the eruption.

Key words: dyke intrusion, remanent magnetization, thermomagnetic anomalies

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