Landslides and tsunamis of December 30, 2002 at Stromboli, Italy: numerical simulations

On December 30, 2002, a series of mass failures occurred in the north-western flank of Stromboli, more precisely in the northern part of the Sciara del Fuoco. Slides were clustered into two distinct complex episodes of failure, separated one from another by about 7 minutes. The first took place mainly underwater, the second one detached from above the sea level. The two tsunamis were generated by the main slides and attacked the Island of Stromboli. The damage was severe, especially on the northern and eastern coast of the island that stretches from Piscit� to Pizzillo, where many houses were destroyed. No deaths were caused by the tsunamis since most houses were empty when the tsunamis attacked and because the few residents or tourists who happened to be there were alerted by the noise accompanying the water waves and were able to escape. The understanding of the event was not immediate and the sequence of facts could be reconstructed only by 1) examining the data acquired by the monitoring system before, during and after such occurrences, 2) carrying out bathymetric and aerophotogrammetric surveys to determine the displaced volumes, 3) performing post-event surveys to ascertain the physical effects of the tsunami on the coast, 4) interviewing eye-witnesses, 5) performing numerical simulations of the events. This study belongs to the last category of activities, since its main purpose is to contribute to the understanding of the complex physical phenomena that occurred at Stromboli. We use numerical codes to simulate the motion of the two main landslides and the generation and propagation of the ensuing tsunamis. This work, that complements previous simulations, focuses on the impact of the waves against the north-eastern coasts of Stromboli: here the computed retreat and flooding of the sea are shown to agree with the eye-witnesses accounts and with the boundary of the inundation zone that was identified during the post-tsunami surveys. The study shows that both tsunamis were powerful, and that the second one was only slightly smaller than the first, though it was produced by the failure of a mass with volume approximately one third of the first. The second tsunami occurred before the first one had concluded its life, superimposing itself on the queue of the first one.