Monitoring compositional changes in volcanic gas chemistry

This paper deals with the problem of identifying extreme compositions in multivariate matrices of chemical data obtained from different fumaroles collected at Vulcano Island (Sicily, southern Italy) between 2000 and 2005 by using Factor Analysis. Four unobservable or latent components were obtained and plotted in a tetrahedron thus reflecting the relative influence of each one of them on each sample. The latent components can be interpreted as due to the contribution of the 1) magmatic activity, that fluctuates probably following the tensional state that dominates in the area, 2) water-rock interactions that register the intensity of the marine signature of the fluids that circulate in the crater area and 3) fumarolic gas contamination phenomena by air, probably to be related to an increase of the fracture density. The plot can be used as a monitoring tool since new samples can be included and their positions with reference to the vertices evaluated.