In all those countries geologically “unsettled”, the history of the various populations, their myths, their religions, the changes in the natural landscape, and volcanoes and seismic events, all come together to form a particularly evident and complex intermingling. This seems clearest in volcanic areas which are often subject as well to recurring powerful Earthquakes, and which include the major centres of the most ancient civilisations on Earth: Central America, Asia Minor and the Mediterranean basin. Among these, the best examples come from Magna Graecia, not only for the extraordinary clarity and continuity of its historical evidence, but also because for many centuries it offered mankind the largest natural Earth science laboratory in the world. Naples – ancient Partenope –is the very emblem of this intermingling in that it is a metropolis with an historical role in the forefront founded in one of the world’s most active volcanic regions.
The Gulf of Naples area is under the heavy influence exercised by the always encumbering (and sometimes devastating) effects of volcanic phenomena. The memory of man records the encounter said to have taken place here between Hercules and the Giants (an early representation of ancient eruptions), as well as hasty evacuations of the city and later rebuilding (documented beginning no later than the II Millennium B.C.). Both in myth and history Vesuvius and fields known as the Campi Flegrei have weighed on urban development in the area. Here it suffices to observe the colour of the city, which is really that of the Campi Flegrei. Not only does tufo giallo, the porous yellow tufa rock, crop up as a natural substratum in green areas, but also constitutes the bricks used in the construction of buildings in the oldest and most popular districts. The black lava flows from Vesuvius reach all the way to within the old part of the city where the streets are paved with large chianche from the volcano, thus reproducing the natural lava theme in the network of streets at the very heart of the city.
In order to interpret these records the geologists have to be called upon. How otherwise to explain what Lyell had earlier pointed out – the presence of holes produced by stone-eating organisms, commonly found on the surface of sea water, a full ten metres above current sea level in the columns by Serapeo in Pozzuoli? Here the phenomenon known as bradyseism, responsible for the continuous local variation in sea level in the Gulf of Naples, appears to play a significant role. From the time of the construction of the Roman market to the time of its maximum submersion the ground level dropped approximately ten metres in the area known as puteolana, but subsequently (probably in the Middle Ages) the phenomenon made its presence felt either upward or down in all the Campi Flegrei (due to pressure exerted by deep-lying magma).
In the mid-XIX Century thanks to Bourbon monarch Ferdinand II the world’s first volcanology observatory was founded, providing a training ground for generations of volcanologists and a model for later such observatories, including the famous ones located in the Hawaiian Islands. With it modern volcanology was born, not far in its minute descriptive detail from the efforts of Pliny the Younger in his Letters to Tacitus describing his uncle’s death in the eruption of 79 A.D., but now better informed by the sciences and with adequate quantitative underpinnings. The founding of the O s s e rvatorio Vesuviano testifies to the understanding reached that Vesuvius was the most complex and dangerous of Italian volcanoes. The Greek geographer Strabo had already sensed Vesuvius’ volcanic nature, but its notoriety grew only with the 79 A.D. eruption which, following a long period of inactivity, destroyed the Roman cities of Pompeii and Herculaneum by covering them with ashes and mudflows. Somma Vesuvius has been active from time to time for approximately 300,000 years, and its current state of inactivity dating from 1944 does not mean that it will now rest forever. The most recent period in its history of eruption from the 1637 eruption to date has been characterized by modest activity, while prior activity was prevalently of an explosive nature with the rain of ashes and pumice and at times also with huge clouds of burning steam, torrents of mud and base surges.
Not much different is the situation at the Campi Flegrei, a young and complex volcanic system formed some 35,000 years ago due to cave-in after an incredible eruption of approximately 80 cubic kilometres of magma which produced the yellow tufa of Naples. It is not mere happenstance that the location of the gateway to Hell has always been indicated as being located here at Lake Averno (meaning “without birds”, since birds were unable to fly through the area because of the volcanic gasses present). Right at the Campi Flegrei in 1538 a volcano of respectable size, Monte Nuovo (meaning "new mountain"), was formed in a matter of days, preceded by Earth tremors, the discharge of gas and the lifting of the earth. If we bear in mind this picture it is easy to understand the vast interest that the Naples area has always aroused in volcanologists all over the world. It must not be forgotten that volcanic risk estimates are based on the probability that an eruption will take place in a given area in relation to its potential for destruction and, therefore, in relation to population density and degree of urbanization. In the entire Gulf of Naples area the level of such risk has been reached and exceeded And that is not all. For some time now volcanologists have engaged in predicting possible scenarios for the next twenty years with the aid of every available description of eruptions from 79 A.D. to date elaborated including with computer simulation.
In these predictions, clearly now as in the past the reopening of the volcanic vent leading to the underground chamber where the magma begins its rise is preceded by related earthquakes, perceptible raising of the ground, the opening of fissures and the formation of fumaroles. The most spectacular phenomenon is initially the rise of a thick column of smoke and steam carrying ashes, pumice and incandescent blocks. The subsequent fallout causes the sky to darken, roofs to collapse, roads to be buried for kilometres and the inhabitants’ lungs to clog. Torrents of mud caused by the accumulation of ashes are possible even a number of days following eruption are among the major causes of urban destruction. When the column of smoke and steam collapses it does so because of an overabundance of solid matter present, meaning that it happens suddenly accompanied by the formation of very thick clouds (called pyroclastic) which travel at 100 kilometres per hour at high temperature destroying everything in their path. All this may occur just two or three days from the onset of eruption, at which time no less than 700,000 persons ought to be prepared for an evacuation of biblical proportions.
A giant step ahead has been taken in the challenge of getting to know “the mountain”, as Neapolitans call “their” volcano, in order to predict its activity. Now it is up to civil defence forces to see to it that there will be no unpreparedness at the next eruption.