The terrible scenes of the eruption of the Honga Tonga volcano (500 times more powerful than the atomic bomb of Hiroshima) have brought back all the widespread fears about similar eruptions also in Italy. Leaving aside the volcano most similar to Honga Tonga, that Marsili that "lies" just below the surface of the water, the suspect number one (I am not saying this because of Naples) is Vesuvius.
Il VESUVIO, the famous volcano of Naples, erupted for the last time in 1944.
History has shown us how dangerous its explosions can be, prompting us to think about a possible method of prevention.
Researchers with experts on volcanoes from ETH Zurich have started a new study, dedicated to analyzing the eruptions of the volcano and its history. The main objective is to develop a theory on a possible new explosion.
The previous episodes, which occurred both in historical times and prehistoric, they brought explosive eruptions capable of destroying entire countries. The people settled nearby have had no chance to save themselves, and the consequences have been catastrophic.
To try to predict the arrival of the new one eruption, researchers from Zurich examined the four largest eruptions of Vesuvius, which occurred in the past 10.000 years.
In particular, they considered: the Avellino eruption of 3.950 years ago; the eruption of 79 AD which buried the Roman cities of Pompeii and Herculaneum (also known as "Plinian eruptions"); the sub-plinian eruption of 472 AD and the eruption of 8890 BC
Garnets in the magma of Vesuvius
The first elements analyzed, taken into consideration to differentiate the different eruptions, are the garnet crystals present in the volcanic deposits
The "garnet" is a unique material of its kind, a mineral that grows from magma when the latter gets stuck in the magma chamber. Knowing the age of the crystals helps to establish how long the magma remained in the chamber before Vesuvius erupted.
In their study, published in the journal Science Advances , the researchers explained the analysis mechanisms of garnet.
To determine the age of the crystals, materials such as uranium and thorium were used.
Garnet has such a structure that it incorporates small amounts of the materials, which can then be measured by experts. Using the ratio of uranium-238 to thorium-230 isotopes, researchers can calculate the crystallization age of the minerals.
The garnets taken into consideration for the development of this study come from the set of materials collected by the ETH team directly "on site".
To ensure the highest level of accuracy, the sites corresponding to the four explosions were chosen for each extraction - the points where debris can still be found.
The age of granite crystals
By elaborating the research and analyzes described above, the researchers were able to understand what is the mechanism behind the explosion.
They understood that the most explosive magma in Vesuvius (the magma called "phonolytic") Is stored in a reservoir in the upper crust for several thousand years before the influx of the hottest magma (the magma called"primitive“), Who is responsible for the explosion.
Apparently, in the two prehistoric events the magma remained in the chamber for about 5.000 years. In historical ones, time has shrunk to around 1.000 years.
All this happens because, as the project manager reminds us Olivier Bachmann, “Vesuvius has a rather complicated hydraulic system”.
Under the volcano there are several magma chambers connected by a system of pipes.
The upper chamber - responsible for the eruptions - fills with magma from one of the lower chambers. Here, the material crystallizes, activating a process called "magmatic differentiation". At this point, the "differentiated" magma takes the name of phonolite.
After a certain time interval, the more primitive or "mafic" magma flows into the upper chamber, generating an increase in pressure inside the chamber. All this pressure pushes the phonolytic magma upward, potentially up to the surface, initiating an eruption.
A phonolithic magma reserve is currently preserved under Vesuvius. Experts wonder how much more remains, and whether the next eruption will be catastrophic or "manageable".
Monitoring of Vesuvius
Currently, it is not possible to determine the amount of magma, both phonolithic and mafic, preserved in the depths of Vesuvius.
However, as the volcano has been producing mainly mafic magma since 1631, researchers believe it is unlikely that differentiated phonolite is currently accumulating.
The hypothesis of a disastrous explosion like the one that destroyed Pompeii and Herculaneum is therefore quite unlikely. The volcano needs a much longer period of quiescence to reach similar levels.
"We think it is more likely that a large and explosive eruption of Vesuvius will occur only after a period of quiescence that lasted centuries." Bachmann revealed.
“However, smaller but still very dangerous eruptions like that of 1944 or even that of 1631 can occur after shorter periods of quiescence. An accurate prediction of the size and style of volcanic eruptions is not possible so far. However, the awakening of the magma reservoirs under the volcanoes are now recognizable by monitoring ”.
To safeguard the citizens who live near Vesuvius, the volcano will be monitored 24 hours a day.
In addition, an emergency plan was prepared for possible evacuation, in order to protect as many people as possible.