Occurrence of inter-eruption debris flow and hyperconcentrated flood-flow deposits on Vesuvio volcano, Italy

In the period between AD 79 and AD 472 eruptions, inter-eruption debris flow and hyperconcentrated-flood-flow deposits were deposited in the Somma-Vesuvio areas. These deposits, forming cliffs at the Torre Bassano and Torre Annunziata, were generated by highly erosive Roods, whose erosive capacity was enhanced by acceleration due to the steepness of the volcano slopes. In this type of deposits were distinguished five depositional facies (from A to E) outcropping well at Torre Bassano where they are stacked in three fining-upward (FU) sequences, probably representing three forestepping - backstepping episodes in the emplacement area of gravity flows. These five facies from coarse to fine are interpreted to represent the downcurrent evolution of particular composite sediment gravity flows characterized by horizontal segregation of the main grain-size population. The blocking of these highly concentrated composite parent Rows would first produce the deposition of the coarse front part to form facies A and then the overriding of this deposit by the bipartite flow, which constitutes the body of the how. This how is composed of a highly concentrated basal inertia carpet responsible for the deposition of facies B, C and D and an upper hyperconcentrated hood flow that forms facies E, through traction plus fallout processes, respectively. Finally, the occurrence of "lahar" type events at Somma-Vesuvio region even at present times is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.