The use of historical sources in the assessment of volcanic scenarios and risk management

The Science of Volcanology traditionally begins with the first text that more or less fully describes a volcanic eruption: the two letters of Pliny the Younger to Tacitus following the explosive eruption of 79 AD that destroyed the Roman cities of Pompeii, Herculaneum, and Stabiae and gave the name of Plinian to this type of eruption. In Italy in the following centuries there have been many eruptions of the many active volcanoes that reside there and many of them have been observed and described, with particular interest in Vesuvius after the Plinian of 1631 entered into semi-continuous activity for more than three centuries, at the gates of Naples, Capital of the Kingdom of the Two Sicilies and one of the most culturally lively and attractive cities in Europe, at least in that period that ends with the Unification of Italy. The attention to volcanoes that have derived from these peculiarities has made Italy the cradle of Volcanology both in the past and in times closer to us and has posed the problem of how to use the enormous paper and iconographic heritage that today we possess together with a few other countries in the world such as Japan, Indonesia, and Iceland. Over time the approach to this problem has gone from an uncritical reading, to disinterest, to pure conservation, to the partial rediscovery of one or a few chronicles and their improper use, to a more correct use of these sources, also including the historical context, to a more modern multidisciplinary approach, up to considering the possibility of an automatic extraction of the data of interest, which represents the challenge we are facing today.  The historical data will allow us to improve the description of the volcanic phenomena of past eruptions and to realize a better comprehension of which territories were affected by past volcanic events and which were the problems that the institutional actors of the time had to face and how they did it, so as not to fall into the same possible errors. In relation to these issues, the correct use of historical data combined with all the various types of volcanological data has already proven to be fundamental both in the definition of eruptive scenarios and in the formulation of emergency management plans. This is the case of the description of the maximum expected explosive eruption and the inclusion of an effusive and fissural scenario never taken into consideration until now in the event of a reactivation of Vesuvius volcano.