Long-term forecasting of the extreme eruptions of Etna

Until now, the widely used predictive long-term hazard models of the most intense natural phenomena do not yield predictions other than the mean return period. To achieve less uncertain estimates, an alternative model is proposed. The analysis of the eruptions of Etna from 1868 to 1993 shows that the time interval D_t between consecutive large eruptions is clearly random, whereas the total volume of tephra ejected during D_t is roughly constant. Taking into account the above evidence, the model yields significant long-term forecasts both of the time and of the intensity of future large eruptions. The large volume of tephra ejected by the volcano since the last intense eruption in 1980 allows the model to estimate that the next large eruption will not to take place soon.