Numerical modelling of the transition from fissure- to central-type activity on volcanoes: a case study from Salina Island, Italy

The evolution of the Rivi-Capo volcanic complex (Aeolian Archipelago) is ch aracterised by a two-stage activity. Early phases of activity developed alo ng a 1.5 km long eruptive fissure, whereas the later phase occurred from a central conduit. Geological and structural data indicate that the transitio n from fissure- to central-type activity was almost continuous in time, and no changes in the composition of the erupted products has been observed. S uch a transition cannot be explained as a consequence of (a) Row localisati on along a dike due to viscosity variation, or (b) emplacement of a magma r eservoir by intersecting propagating cracks, or (c) re-orientation of the s tress within the volcano due to gravity processes. In order to explain the change in vent geometry, a finite-element model has been developed which, u sing reliable parameters for basaltic rocks, accounts for a progressive mel ting of the host rocks enhanced by the flow of hot magma in the partially m olten region. The proposed model allows one to explain the transition from fissure to central vent activity observed at Rivi-Capo as well as on other volcanoes. (C) 2001 Elsevier Science B.V. All rights reserved.