Occurence of inter-eruption debris flow and hyperconcentrated flood-flow deposits on Vesuvio Vulcano

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 ‹ 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.