Description of the volcanic risk
Even though less frequent and devastating than earthquakes, volcanic eruptions are still a great hazard for the densely populated zones in the Italian territory.
A volcanic risk can be defined as the product of the probability of an eruptive event to occur for the probable harm that could be derived.
The hazard can be represented by the equation R = H x V x E, where:
H = Hazard: is the probability that a phenomenon of a certain intensity will occur in a certain period of time in a determined area;
V = Vulnerability: the Vulnerability of an element - persons, buildings, infrastructures, economic activities – is the propensity to suffer harm subsequent to the stress induced by an event of a certain intensity;
E = Exposure or exposed value: is the number of units, or “values”, of each one of the elements at risk, such as human life or houses, in a determined area.
In general the vulnerability of persons or buildings is always high with volcanic phenomenology. The hazard is minimum only when the hazard or exposed value is minimum also. This is the case of “extinct” volcanoes, volcanoes of a low hazard phenomenology; or else volcanoes located in uninhabited areas.
The greater the probability of eruption the greater the risk. But the risk increases at the same time as the hazard as urbanization increases in areas surrounding the volcano. As an example, the risk is higher with Vesuvius with about 600 thousand people living around it, rather than the volcanoes in Alaska, located in zones with a low population density.