Vulcano and Stromboli: Self-potential mapping and dipolar geoelectric tomography

We present the results of the geoelectrical survey program carried out at the Vulcano island during 1993-95. The program started in 1991 and has regularly continued until 1995 with systematic repetition of self-potential (SP) and dipolar geoelectric (DG) measurements. The aim was to study the time variations of the underground fluid circulation, which are hypothesized to be connected with the volcanic activity in the island. Particular care was devoted to understand also the influence of rain percolation and sea-water inland invasion on the distribution and amplitude of the observed SP anomalies. As it concerns the DG investigation, we performed twelve new tomographies along a profile located at the base of the Fossa crater, which is the one where we had observed the strongest variations of resistivity. We reasonably admit that the observed resistivity time-variations may be closely linked to the presence/absence of fluids (sea-water) in the highly fractured volcanics down to a depth of about 400 m, sometimes even down to about 700 m, from the ground level at the base of the Fossa Crater.