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Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133-Milano, Italy
The island of Stromboli represents the emergent part of a 2.6 km high composite volcano. The evolution of this summit zone is characterized by a complex dyke pattern and repeated collapses. Three summit collapses and one southeastward minor lateral collapse occurred between 85 and 21 ka BP. 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 along the NE-trending weak zone, whereas the other 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 to the local
3 induced by debuttressing, in the case of injection planes parallel to the lateral collapse escarpments, and by the gross volcano morphology, in the case of dykes which parallel the cone slopes.
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