Over the centuries, many communities have established around Vesuvius making it one of the most densely populated areas in Italy. Over 550,000 people live on its slopes and this is why it is considered one of the volcanoes at the highest risk in the world.
Throughout history, Vesuvius has been marked by alternating periods of eruptive activity with open duct, and rest periods with blocked duct, characterized by the absence of eruptive activity and accumulation of magma in a magma chamber in depth.
These periods are interrupted by very energetic eruptions, which are then followed by periods of open duct activity with frequent effusive eruptions or explosive eruptions with low energy.
The 1631 eruption has interrupted a break that lasted for nearly five centuries. From 1631 to 1944 volcanic eruptions have been constant and interspersed with rest periods of a few years.
According to recent studies, the most likely volcanic event most likely to happen is a violent strombolian eruption (VEI = 3), with relapse of pyroclastic materials and the formation of mudflows or lahars. Moreover, a research conducted from geophysical surveys has not detected the presence of a magma chamber surface with sufficient volume to generate an plinian eruption. Therefore an event of this type is unlikely to happen.
On the basis of these observations, the committee in charge of updating the Plan has determined that the reference scenario is a sub-Plinian-type event, similar to that of 1631 and comparable to the one examined in the previous Plan. This scenario involves the formation of a sustained eruptive column several kilometers high, the fall of volcanic bombs and blocks immediately around the crater and particles smaller - ash and lapilli - up to several tens of kilometers away, and the training pyroclastic flows that would flow down the slopes of the volcano for several kilometers.
Based on this scenario, areas - for which it was designed a National Plan of emergency which provides differentiated actions - potentially subject to various phenomena expected have been identified.