Figure 4

Retrospective application of BETEF_CF from 1981 on. At each time t₀, BETEF_CF is calibrated with the data for t<t₀. In panel A, we report the average (best estimate) probability of unrest (blue), magmatic unrest (green) and eruption (red) for the following 1 month. In panels B, C and D, at three different time, we report a snapshot of the cumulative distribution (percentiles) of the probability of eruption, highlighting the epistemic uncertainty on the estimated probability. Spikes in the probability values (main figure) represent unrest episodes, during which monthly probabilities are much greater than the background ones. The major unrest period 1982-84 (Barberi et al. 1984), as well as each one of the minor uplift phases that followed, are correctly identified as anomalous. In particular, BETEF_CF shows that starting from mid-1982 the volcano was certainly in an anomalous state (probability 100%at node 1), the average probability that the unrest was due to active magma movements was about 70%, and the probability of an eruption on a time window of one month was about 20%, with a peak of nearly 40%in the period June-September 1983 (in October the evacuation took place). Such a high value is in agreement with the perception of some volcanologists at the time (Civetta and Gasparini 2012), even if explicit quantifications of probabilities were not available. In late 1984 the eruption probability returned to lower values around 10%, and the crisis was definitely over at the beginning of the following year. The so-called mini-uplift phases that punctuated the activity of CFc from year 2000 are similar to each other in terms of probabilities, with the eruption probability always less than 10%.