Press release on the activity of Etna and Stromboli, 19 August 2011

Drs. Sergio Gurrieri (INGV-Palermo), Domenico Patanè (INGV-Osservatorio Etneo, Catania) and Mauro Coltelli (INGV-Osservatorio Etneo, Catania) during the press conference on 19 August 2011. Photo taken by Alfio Amantia, INGV-OE Catania

At 10 h on 19 August 2011, a press conference was held in the building of the INGV Osservatorio Etneo - Sezione di Catania, whose subject was the recent and current activity of Etna and Stromboli. Presentations were given by Dr Domenico Patanè, director of the INGV Osservatorio Etneo – Sezione di Catania, Dr Sergio Gurrieri, Director of the INGV Sezione di Palermo, and Dr Mauro Coltelli, Responsible of the UF Volcanology and Geochemistry of the INGV-OE.

On the occasion of the press conference, the attendees received the following press release on the “State of activity of Etna and Stromboli”.

19 August 2011 at 10:00 h

at the INGV Osservatorio Etneo - Sezione di Catania , Piazza Roma, 2, Catania

Presenters:

Dr. Domenico Patanè             Director of the INGV Osservatorio Etneo – Sezione di Catania

Dr. Sergio Gurrieri                 Director of the INGV Sezione di Palermo

Dr.  Mauro Coltelli                 Responsible of the UF Volcanology and Geochemistry at INGV-OE

Titles:

D. Patanè : The monitoring system of the Sicilian volcanoes and volcano surveillance

S. Gurrieri: The role of geochemistry in volcano monitoring

M. Coltelli: The recent eruptive activity of Etna and problems related to volcanic ash. Eruptive activity of Stromboli

Press release

The aim of the conference is to inform the press and the public on the state of the activity of Etna and Stromboli, and to present the upgraded and revamped observation systems at these volcanoes, which have allowed to reach an unprecedented level in the forecasting of eruptions.

As for Etna, there is currently no evidence that a “Big Eruption” or “The Super Eruption” is imminent. It should be emphasized that the expression “Big Eruption” evokes thoughts of a destructive event such as the 1928 eruption that destroyed the village of Mascali, or the still larger and more notorious 1669 eruption, which destroyed nine villages and a portion of the city of Catania. The usage of such expressions understandably generates apprehension in the population. The information should therefore be checked with the responsible staff of the Istituto Nazionale di Geofisica e Vulcanologia and of the National Department of Civil Protection (Dipartimento Nazionale della Protezione Civile), which are the organisms formally charged with the seismic and volcano surveillance on the Italian territory, albeit following different tasks. Treating such a fascinating, but also complex matter such as the study of volcanoes in a superficial manner and with scant knowledge, does not render any service to the public.

Following about 20 months of magmatic recharging, Etna started giving the first evident signs of reawakening in August 2010, with a reactivation of its summit craters, and in January it entered into a new eruptive period, characterized by paroxysmal eruptive episodes from one of its summit craters, the Southeast Crater. All of these events have been preceded by clear and conspicuous variations of most geophysical and geochemical parameters recorded by the multiparameter monitoring network, which already from 2010 on allowed recognizing significant variations, a symptom that something was changing within the volcano.

More recently, the elevated frequency of the paroxysmal lava fountaining activity, which between 9 July and 12 August has led to 6 paroxysmal eruptive episodes, is related to notable variations in the volcanic feeder system, revealed by the deformation of the volcanic edifice from late May to early July. This deformation episode, caused by the arrival of a gas-rich batch of magma, has ceased after the 12 August eruptive episode, and the “excess energy” within the superficial magma reservoir, located within the volcano at about 1000-2000 m above the sea level, has temporarily exhausted its impact. At the current state, therefore, the volcano seems to have returned to a metastable state, and will possibly pursue its activity as before, with episodic paroxysmal events.

As of today, there is no sign that the activity of Etna will evolve, in the near future, toward a type of eruption different from the recent eruptive episodes. It is likely that the evolutionary process of the current activity will eventually lead to an effusive flank eruption, but in this moment it is impossible to say where and when this will happen, and this will remain so unless the typical forerunning signals appear, which precede all flank eruptions at Etna.

It must be specified that predicting an eruption means to determine the time and site of a future eruption, as well as its typology and intensity. Up to now, as for earthquakes, there is no way to express an eruption prediction in the deterministic sense. The prediction of an eruption has to be understood as a probabilistic forecast, which defines the likelihood that an eruptive event of a certain typology and size might take place in a determined time period. Furthermore, it has to be acknowledged that volcanology cannot and must not be seen as a scientific branch in the strict sense of the word, but a sector where different scientific disciplines are applied, and right therein dwells its intellectual force and its power of investigation.

For exactly this reason, the opinion of a researcher or of an expert in one of the disciplines in volcanology can render only a partial and personal view, which is based on the individual specialist’s experience. A hypothesis of an eruption forecast voiced in that manner runs the risk of being still less reliable than a probabilistic forecast based on the integration of all data derived from a complex monitoring system like the one on Etna, and on discussion and comparison made by various experts in the sector.

Finally, regarding Stromboli, the effusive 2002-2003 eruption represents a pivotal moment in the evolution of the monitoring system and in research on this volcano. It is therefore necessary to bear in mind that the time frame within which the new observation system is running is too short to give any certainty or temporal information concerning the approach of an effusive eruption and/or a paroxysmal explosive event. However, the various signals recorded by the new monitoring system prior to the effusive eruption of February 2007 allowed announcing this eruptive event.

Currently, Stromboli is in a state of elevated activity, which, however, corresponds to the normal fluctuations of the eruptive activity of the volcano, as observed in the past 20-30 years. The recently observed eruptive phenomena, such as the major explosions and episodic lava overflows, are clearly related to a phase of pressurization and degassing of the summit magmatic feeder/reservoir system, and might indicate that this system is in an unstable equilibrium. As for now, though, these phenomena do not significantly alter the hazard state of the volcano. Yet, the periodic occurrence of “significant” and unpredictable phenomena like those recently observed certainly requires a heightened state of attention both in the crater area and at the Sciara del Fuoco.

Domenico Patanè, Sergio Gurrieri, Mauro Coltelli