Etna, with its 3350m above sea level and 35 km in diameter at the base, is the largest volcano in Europe. Located along the east coast of Sicily, with an area of 1250km2 and is bordered to the north by Nebrodi and Peloritani and south by the alluvial plain of the river Simeto.
It formed about 100,000 years ago. Over the years , the alternation of effusive and explosive activity , with lava flows and pyroclastic deposits , led to the stratification of volcanic products. For this , Etna is defined as a layer - volcanic basaltic nature.
Its eruptive vents are located at the summit of the volcano and the Bocca Nuova, Voragine Cratere of north -east and Cratere of south -east . Each of them has a diameter of about 200 meters. On the slopes of the volcano are also hundreds of small " adventitious " cones, that have arisen over the millennia during eruptions from the lateral sides.
The morphological structure of the main volcano is the Valle del Bove, a depression that opens to the sea , on the eastern flank of the volcano. The valley is about 5 km wide and 8 km long, and the escarpment , in its steepest is 1200m high. Its origin dates back to around 10,000 years ago, when the succession of explosive caused some collapses or landslides along the side of the volcano.
The alert level for Etna is yellow.
The Civil Protection Department regularly organizes videoconferences with the Centers of Competence responsible for the monitoring of volcanic activity on Etna: the National Institute of Geophysics and Volcanology (Ingv) of Catania and Palermo, the Department of Earth Sciences of the University of Florence and the Institute for the electromagnetic survey of the environment (Irea) of the CNR-National Research Council. The Department of Civil Protection of the Sicilian Region also takes part in the videoconferences.
On the basis of the phenomena and risk assessments made available by the Centers of Competence, the Department of Civil Protection declares the levels of alert and operational phases in close collaboration with the structure of civil protection of the Sicilian Region, after hearing the opinion, if the timing and mode of evolution of volcanic phenomena allow it, the Commission Great Risks - Volcanic Risk Sector.
At the outcome of the videoconferences, the Department issues a document reporting the results of the videoconferences.
Currently the level of alert for Etna is yellow.
The Department of Civil Protection, in agreement with the Sicilian Region and with the support of the Centers of Expertise, introduced from February 1, 2016 some changes to the structure of the national warning system for volcanic risk. In particular for the Etna volcano, these changes were aimed at better framing the responsibility profiles and competences of the different institutional and territorial levels, both with respect to hazard and risk assessment and with respect to the activation of the operational response in case of local or national impact scenarios.
Alert levels. Alert levels describe the state of volcano activity, i.e. whether the volcano is in a state of equilibrium or disequilibrium. They are identified based on a combination of monitoring parameters and data from any ongoing events. They are represented by four colors - green, yellow, orange and red - which are indicative of the possible evolution of the state of volcano activity towards event scenarios "of national importance", which require to be faced with extraordinary means and powers, through the coordinated intervention of a plurality of subjects (art.2, paragraph 1 letter c of Law 225/92).
Declaration of alert levels. The levels of alert are declared by the Department of Civil Protection, in close collaboration with the structure of civil protection of the Sicilian Region, after hearing the opinion, if the timing and mode of evolution of volcanic phenomena allow, the Commission Great Risks - Volcanic Risk Sector.
The assessment is based on the reports of the phenomena and risk assessments provided by the Centers of Competence: the Etna Observatory of the National Institute of Geophysics and Volcanology and the University of Florence. The Department of Civil Protection shares all this information with the structure of civil protection of the Sicilian region that, especially in relation to scenarios of local impact has the task of alerting the territorial structures of civil protection and adopt any measures in response to emergency situations.
Passage of alert level. The passage from one level of alert to another can occur before the phenomena, if the information provided by the Centers of Competence allow it. On the contrary, the passage can be declared when the phenomena are observed, thus after or during the phenomenon. In this regard, it is useful to emphasize that the passage of the alert level may not necessarily occur sequentially or gradually, as sudden or abrupt changes in volcanic activity are always possible, even completely unexpected.
It must be kept in mind that some phenomena of Etna are completely unpredictable and sudden, therefore even when the alert level is "green" the risk is never absent. When these events occur, unaccompanied by anomalies of the monitoring parameters or by further phenomena, the alert level is not necessarily varied, since a condition of "local emergency" is determined that requires the activation of the local civil protection structures.
The eruptions of Etna are mostly characterized by Strombolian activity, effusion of lava flows and ash emissions. They can occur from the summit craters or vents that open on the flanks of the volcano, resulting in many cases in temporary cones as those found in large quantities on the slopes of Etna. The Strombolian activity generally affects a limited area around the vent and is not an agent of risk to to built up areas.
The lava flows of Etna, due to their viscosity and consequent low sliding speed, are not such as to constitute a danger to the safety of people . In the case in which the leakage occurs from the mouths placed at high altitude, the flows would rarely reach the towns . Only in the case of eruptions of long duration, such an eventuality can occur.
In the event that the lava flows threaten a town, it is usually possible to implement measures aimed at altering their path , using different techniques that range from the construction of barriers on the ground, in reinforced canal banks to cause it to flow in a different direction, in the excavation of canals, etc, as it has already been done during the eruptions of 1983, 1992, 2001 and 2002. It should be noted that in the last two cases , interventions were designed to protect tourist infrastructures located at high altitudes, well away from population centers.
A major risk can occur when the lava effusion comes out of vents placed at low altitude: in such case the time to carry out any cooling flows would clearly be reduced and most probably it would be useful to resort to the evacuation of the population from threatened areas , in accordance with the plans.
Ash emissions, quite frequent, although not constituting a risk factor for human life, can cause significant disruption to the transport sector, economic damage, and prolonged exposure without precautions, respiratory diseases . The fallout of ash causes considerable damage to agriculture, severe disruption to air traffic and to the management of Catania Fontanarossa , Sigonella and Reggio Calabria airports.
The preventive measures taken in the event of a relapse of large amounts of ash, as during the 2002-2003 eruption , provide for the distribution of protective masks - to prevent respiratory complications -, cleaning the roofs of houses , streets and highways, in order to avoid accidents and clogging sewage systems.
For the surveillance of Etna's activity status, there are different monitoring systems that measure geophysical, geodetic and geochemical parameters. The number of permanent seismic stations present at the medium-high altitudes of the volcano, allows to perform an accurate control of the local seismicity also of low magnitude. In addition, some of the installation sites are multi-parametric systems that host infrasonic stations, accelerometric sensors, Gps and weather stations.
The monitoring network is also based on the observation of images recorded by surveillance cameras, operating in the visible and thermal bands and located on the eastern and southern slopes of the volcano, as well as the analysis of images acquired by Meteosat satellite and high-resolution radar satellite images of the Cosmo-SkyMed constellation, which allow the observation of the volcano even in case of cloud cover.
The instrumental monitoring system present on Etna is among the most advanced in the world and usually allows to predict in advance the beginning of an eruption. In particular, it allows to foresee above all the lateral eruptions that, for their characteristics, are normally preceded by well identifiable seismic sequences that allow to individuate the area in which the eruptive mouth will open.
Etna reaches an altitude of 3350m, therefore hikers must keep in mind that, although the Sicilian climate is particularly mild, going up in altitude one encounters high mountain conditions, with much lower temperatures and frequent gusts of wind. Moreover, the passage from the sea level to the high mountain within a few kilometers, determines sudden meteorological changes due to the currents of humid air coming from the sea which meet with the masses of cold air. For those who intend to make the excursion, it is therefore advisable to dress with hiking shoes, windbreaker and cap to protect themselves from the sun and to bring with them water and food.
Before hiking it is also essential to find out about the state of activity of the volcano and the risks to which you expose yourself. For the excursions it is therefore advised to turn to the authorized guides, unless you have a good and continuously updated knowledge of the territory and of the dangers connected to the volcanic activity.
Also, it is necessary to consider that the maps available on the market may not be updated: the frequent eruptive phases in fact change continuously and deeply the morphology of the places, creating new cones and rough lava fields.
Mount Etna is located in the continental collision between the Eurasian plate and the African plate . In this area, the presence of an important system of extensional faults has allowed the ascent of magma from the mantle, giving rise to volcanism.
The oldest rocks of the volcano were generated during submarine effusive eruptions that occurred about 550,000 years ago. In this period the area surrounding Mount Etna was occupied by a vast gulf and the lava pouring out from fractures of the seabed , cooling quickly in contact with water, gave rise to so-called pillow lavas, still visible on the rock of Aci Castello . From about 300,000 years ago, eruptions in the emerged environment then followed.
Until recently, the Etna volcano was considered a predominantly effusive volcano , that is mainly characterized by lava flows emissions. Actually, in the last 15,000 years, its activity was characterized by recurrent eruptions, some of which have originated caldera.
In the last hundred years came in succession, with a certain frequency, low-energy explosive eruptions and lava effusions , fueled both by the eruptive volcano's summit and from side vents. These eruptions - lasting a few days or even years - have repeatedly damaged the urban areas that are located on the slopes of the volcano , due to the accumulation of ash and slag and the shift of the lava flows.