Magmatic intrusion determined from self-potential and magnetic measurements at Mt.Etna

The 1989 eruption of Mt. Etna was characterized by the opening of two fracture systems spread from the South-East summit crater base with approximate North-East and South-East trends, respectively. The northern fracture system fed a lateral eruption, whereas the fracture system of the southern side did not seem to take up magma, even though it shows elements of compatibility with a shallow dyke intrusion. With the aim of explaining whether the southern system was really connected to a dyke, during October 1989 a self-potential profile 1320 m long and a magnetic profile 2230 m long were realized at the altitude of 1650 m, orthogonally to the direction of the above mentioned system. The measurements, executed many times until September 1991 for the magnetism and April 1993 for the self-potential, allowed us to reveal marked anomalies tied to phenomena of rock fracturing and fluid invasion for the self-potential anomaly, and to progressive magnetization of cooling dyke for the magnetic anomaly. The magnetic anomaly indicates that the dyke would appear to be c.a. 4 m thick and to culminate ca. 400 m under the topographic surface. Accordingly, the self-potential anomaly suggests that positive charge would accumulate inside a newly fractured zone above the dyke ranging from ca. 150 m to ca. 400 m below the ground level, while the negative charge accumulations appear at both sides of the dyke at a lesser that (from less than 100 m to about 250 m at most) and separated from the positive nucleus by a horizontal spacing of some hundred meters.