Mechanism of landslide causing the December 2002 tsunami at Stromboli Volcano (Italy)

Between December 29th and 30th 2002 the NW flank of Stromboli volcano (Sciara del Fuoco) was involved in a series of large-scale instability phenomena which culminated in submarine and subaerial destructive landslides provoking two tsunami waves with a maximum run-up of 10 m. In this paper, part of the results of a joint research between the National Research Council (Italy) and the Disaster Prevention Research Institute of Kyoto University (Japan) is presented. The activity has focused on the mechanical characterization of the volcanoclastic material forming the Sciara del Fuoco depression and the interpretation of landslide mechanisms on the basis of large-scale ring shear tests. Attention is given here to the initiation and propagation of the submarine landslide which caused the first tsunami. In order to investigate the material response to different displacement rates in terms of shear resistance, pore pressure generation and grain crushing, ring shear tests were conducted in both undrained and drained conditions. Experimental results indicate that a fully or partial liquefaction mechanism can be invoked to explain the failure of the submarine flank of the Sciara del Fuoco and the long run-out which followed, as it was suggested by comparing pre- and post-failure in situ observations.