Occurrence of inter-eruption debris ¯ow and hyperconcentrated ¯ood-¯ow deposits on Vesuvio volcano, Italy L. Lirer a, * , A. Vinci b , I. Alberico c , T. Gifuni a , F. Bellucci a , P. Petrosino a , R. Tinterri b a Dipartimento di Geo®sica e Vulcanologia, Via Mezzocannone 8, Universita Á di Napoli Federico II, 80134 Napoli, Italy b Dipartimento di Scienze della Terra, Viale delle Scienze 157/a, Universita Á di Parma, 43100 Parma, Italy c Centro Interdipartimentale di Ricerca ªAmbienteº Via Mezzocannone 16, Universita Á di Napoli Federico II, 80134 Napoli, Italy Received 1 December 1999; accepted 14 September 2000 Abstract In the period between AD 79 and AD 472 eruptions, inter-eruption debris ¯ow and hyperconcentrated-¯ood-¯ow deposits were deposited in the Somma-Vesuvio areas. These deposits, forming cliffs at the Torre Bassano and Torre Annunziata, were generated by highly erosive ¯oods, whose erosive capacity was enhanced by acceleration due to the steepness of the volcano slopes. In this type of deposits were distinguished ®ve depositional facies (from A to E) outcropping well at Torre Bassano where they are stacked in three ®ning-upward (FU) sequences, probably representing three forestepping Ð backstepping episodes in the emplacement area of gravity ¯ows. These ®ve facies from coarse to ®ne are interpreted to represent the downcurrent evolution of particular composite sediment gravity ¯ows characterized by horizontal segregation of the main grain-size population. The blocking of these highly concentrated composite parent ¯ows would ®rst produce the deposition of the coarse front part to form facies A and then the overriding of this deposit by the bipartite ¯ow, which constitutes the body of the ¯ow. This ¯ow is composed of a highly concentrated basal inertia carpet responsible for the deposition of facies B, C and D and an upper hyperconcentrated ¯ood ¯ow that forms facies E, through traction plus fallout processes, respectively. Finally, the occurrence of ªlaharº type events at Somma-Vesuvio region even at present times is discussed. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Vesuvio; Laharic deposits; Facies analysis; Debris ¯ow; Hyperconcentrated ¯ow; Composite sediment gravity ¯ow 1. Introduction Volcanism-induced sedimentation has been recog- nized in ancient volcaniclastic sequences as well as in numerous modern active volcanoes (e.g. Mount St. Helens-1980, Nevado del Ruiz-1985, Mayon-1984, Pinatubo-1991). When pyroclastic deposits are mainly made up of pyroclastic debris emplaced from strato-volcanoes whose steep slopes rapidly degrade towards plain surfaces or coast-lines, they are expected to make a large contribution to sedimenta- tion of epiclastic deposits, as a consequence of the rapidity of erosion and transport of loose particles by heavy rains of short duration. These climatic phenomena are quite typical of temperate climates in Mediterranean areas, where rains are concentrated in some parts of the year (mostly autumn and spring) and can reach high values in few hours (De Vita and Vallario, 1996). In the Somma-Vesuvio region, and mostly in the Torre del Greco area (Fig. 1), volcaniclastic deposits Sedimentary Geology 139 (2001) 151±167 0037-0738/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0037-0738(00)00162-7 www.elsevier.nl/locate/sedgeo * Corresponding author. Fax: 139-81-5525739. E-mail address: lirer@biol.dgbm.unina.it (L. Lirer).