Active volcanoes in densely populated areas represent a major natural hazard that influences and guides the territory management policy and requires a strong and effective interplay of the societal components (science, engineering, policy makers). This has led to the implementation of in-situ volcano monitoring systems worldwide, as well as an increasing interest of Earth Observation (EO) missions to acquire geophysical and geochemical parameters linked to the volcanic activity.
In Europe, the south of Italy is a clear example of such a situation, where various areas are threatened by virtually all types of volcanic hazards (from lava flows to tephra falls, pyroclastic flows, lahars, and widespread ash clouds affecting international air traffic). The metropolitan area of Naples (more than 2 million of inhabitants with a density > 2.600 inhabitants/km2) has grown within the Campi Flegrei caldera and around Vesuvius volcano ; both volcanoes have shown highly explosive volcanism throughout their geological histories and into historical time. A new eruption is expected to produce 10-30 km-high volcanic columns, ash cloud dispersal over substantial portions of Europe and beyond (depending on wind directions), and devastating pyroclastic flows. The area of Naples is one with the highest levels of volcanic risk worldwide also considering that, since the 1950s, a phase of unrest is under way in the Campi Flegrei caldera, whose macroscopic effects resemble those of phenomena that preceded its most recent eruption in 1538. Therefore, a volcanic eruption would have the potential to cause a crisis of European proportions.
The challenge from future eruptions in this densely populated area requires the most avant-garde monitoring methods and techniques to be applied, in order to capture and correctly interpret premonitory signs of unrest in time to permit an adequate response. This Task is rather delicate also because of the risk of a false alarm that could cause partial to total disruption of social, cultural, and economic life and bring hardship to an exceptionally large number of people. Conversely, late warning of an unusually rapid eruption onset can result in a rather chaotic response, with a high risk of economic and human losses.