Radionuclides and sulfur content in Mount Etna plume in 1983-1995: new constraints on the magma feeding system

Radionuclide activities (Pb-210, Bi-210, Po-210) were investigated, in Moun t Etna plume from 1983 to 1995. At SE crater the longterm observation (12 y ears) of the Po-210/Pb-210 ratio shows that it can behave as a degassing ve nt not directly related to the main magma reservoir depending on the magma level inside the volcano. Since 1992, the simultaneous determination of rad ionuclides and sulfur in the main plume results in new constraints on the d egassing model of Lambert et al. (Earth Planet. Sci. Lett., 76 (1986) 185). The Po-210/SO2, and Pb-210/SO2 ratios enable us to identify two sources of Po-210 in the plume: one is magmatic, correlated With SO2, the other one i s an additional component issued from the decay of Pb-210 in the shallow de ,gassing cell, and depends directly on the residence time of the gases befo re their emission. Estimations of the volume of degassing magma, the reside nce time of the gases and the proportion of undegassed magma renewing the s hallow degassing cell are given for the period 1992-1995. During the 1992 e ruption, the rate of degassing magma volume is estimated to have been as hi gh as 5 X 10(6) m(3)/day, and the volume of the shallow degassing magma res ervoir about 0.5 km(3). In 1994 and 1995 the rate of non-erupted degassing magma volume was estimated to have been about 0.18 km(3)/year. During the e ntire 1983-1995 period, only 15-20% of the degassed magma was erupted. (C) 2001 Elsevier Science B.V. All rights reserved.