During the time January-June 2000, the fountains of lava, with bombs of several decimetres reached heights higher than 1000m and the fine materials as ashes several kilometres. In the diagrams are deferred the contents of major elements expressed in oxide weight compared to the content of SiO2 regarded as index of differentiation. It is noted that the points representative of the composition of the lava are laid out according to lines, which represent a process of mixture accompanied by a process of crystal fractionation. It is necessary to go up with the eccentric eruption of Monte Fiori in 1974 to find contents of the same command. The alkaline ones, contrary to the other elements, present a positive correlation with silica, in other words they concentrate in the residual liquid during differentiation.
Caption diagrams below.
The follow-up of the composition in major elements and traces on total rocks and inclusions vitreous, of the products emitted during various eruptions of Etna, brings information to us on the eruptive processes and the mechanisms of feeding of the volcano. For that, certain chemical elements obey simple laws and can be used like tracers of the nature of the lava. We will take here the example of thorium, element having the property to remain in the molten phase of the lava and to be insensitive with the separation of the crystals and gases. In general, these various craters are active separately but it happens sometimes that several craters function at the same time. Thegeochemical follow-up that we carry out since 1983 us led to call into question the generally allowed idea that these various craters were fed by a surface tank.