Mutual influence of dyking and collapses at Stromboli volcano, Italy

Abstract: The island of Stromboli represents he emergent part of a 2.6 km high composite volcano. The evolution ofthis summit zone is characterized bya complex dyke pattern and repeated collapses. Three summit collapses and one southeastward minor lateral collapse occurred between 85 and 21 kaBP. From 13 ka to a few thousand years ago, three large lateral collapses occurred northwestwards. During the last 100 ka of volcanic history, which is reconstructed on the basis of data derived from the emergent part of the cone, the majority of dykes have been injected along a NE-SW zone of weakness which cuts the summit of the volcano. In the southern part of the island a N-S dyke zone connected, for a short period, the main Stromboli conduit to an off-shore crater. Another dyke zone developed after 13 ka BP along the walls of the earliest lateral collapse which occurred towards the NW at around this time. Dykes are vertical, especially ong the NE-trending weak zone, whereas theother more external dykes tend to parallel the cone slopes and the collapse depression. Cumulative dyke thicknesses have a NW-SE horizontal maximum. Dyking along the NE-SW weak zone may have exerted a geometric control and provided a trigger for the NW-SE lateral collapse event. In turn the more external dyking was extremely sensitive o the local ~r3 induced by debuttressing, in the case of injection planes parallel to the lateral collapse escarpments, andby the gross volcano morphology, in the case of dykes which parallel the cone slopes. The island of Stromboli and two other volcanic centres constitute a large, 2.6 km high, volcanic complex at the NE tip of the Aeolian archipe-lago (Fig. 1). The Stromboli volcano constitutes the island of that name; Strombolicchio is a volcanic neck forming a small island to the north east; and Cavoni is a submerged centre identified on the basis of marine geophysical data (Gabbianelli et al. 1993) to the south. The internal structure of Stromboli volcano is complex because of the alternating constructive and destructive phases. The latter range from slow, slope-erosive processes to rapid slope failure, and have created several unconformitie