Monitoring Volcanic Eruptions Using Trace Metals In Tree-Rings: Preliminary Results From Mt. Etna

Abstract

Active volcanoes can influence surrounding vegetation both through passive degassing during quiescent periods and through eruptive degassing, by introducing into the atmosphere several metals as gases and particles. The chemical composition of tree-rings has been generally used to investigate the effects of anthropogenic gas emissions and dendrochemical methods have successfully recorded variations in the pollution levels. The use of tree-rings analysis in active volcanic areas has shown that vascular plants could be used as archives of volcanogenic metals deposition. Tree cores of Pinus Nigra and Populus tremula were collected in sites located both on the downwind (Citelli and Mt. Fontane sites) and on the upwind (Mt. Intraleo site) sectors of Mt. Etna in June 2008. Individual and composited tree-rings were analyzed by inductively-coupled-plasma mass-spectrometry for the determination of several trace elements (As, Cd, Li, Mn, Mo, Ni, Se, Sr, Pb, V). Tree cores were dated dendrochronologically before analysis, and their ages date back to 1915. The preliminary results show that some elements have significant differences in concentration between the two tree species analyzed, and in general metals are more concentrated in the samples from the downwind sites, hence more exposed to crater gas emissions. Furthermore, the temporal patterns of metal contents show some evident peaks likely related to some of the major flank eruptions of the volcano, particularly those occurred after 1945. This method can be used in many active volcanoes to reconstruct their past degassing rate and recognize possible eruptive cycles, thus helping forecast their future behaviour.