The Secche di Lazzaro pyroclastics of Stromboli volcano: a phreatomagmatic eruption related to the Sciara del Fuoco sector collapse

Abstract

Widespread phreatomagmatic ash deposits (Secche di Lazzaro pyroclastics) overlying the lavas of the Neostromboli period (13000 to ca. 5000 years B.P.) have been identified at Stromboli volcano. The deposits consist of accretionary lapilli-rich ash-fall layers and debris flows. Ash-fall layers originated by phreatomagmatic explosive activity from a vent probably located in the uppermost part of the sector-collapse scarp (Sciara del Fuoco) which formed at the end of Neostromboli period. Stratigraphic position, composition of fresh lapilli identical to the Neostromboli lavas, and an unusually large scale of explosions suggest that the Secche di Lazzaro pyroclastics were erupted in connection with the Sciara del Fuoco slope failure. Characteristics of the deposits are consistent with phreatomagmatic/hydrothermal explosivity related to catastrophic decompression of the plumbing/hydrothermal system. Occurrence of multiple ash-fall episodes, coupled with variation of nature of lithics lithology, is suggestive of repeated explosions eventually triggered by multiple, backward-migrating block detachments.