Groundwater Level Variations in relation to Volcanic and Seismic Events. New Insights on Mt. Etna, Southern Italy

In this preliminary study, the response of Etnean groundwater levels (GWL) to seismic and volcanic events between 2003 and 2007 was investigated. This period was characterised by frequent volcanic and seismic activity. Groundwater timeseries were filtered for the effect of meteoric contribution by employing the Cumulative Rainfall Departure (CRD) approach; these were then examined for correlations with volcanic and/or seismic events. Noteworthy variations in GWLs were observed in the proximity of eruptive episodes. These seemed to be consistent with the variation of other parameters such as ground deformation and SO2 emissions previously investigated by other authors, and with the GWL fluctuations preceding the 2001–2002 seismic-volcanic crisis, detected by the Geochemical Monitoring System (GMS–2). Additionally, the variations observed before the phreatomagmatic explosion of January 12th, 2006, were the most evident among the whole examined period. With regard to this latter event, the GWL of wells to the S/SE sector of the volcano displayed a sudden and quasi-simultaneous lowering. These fluctuations commenced in November 2005 and were coincident with a moderate increase in the amplitude of volcanic tremor and mild inflation of the summit of the volcano, as recorded at permanent GPS stations. Less marked results have been obtained in relation to seismic events and it has not been viable to identify recurrent patterns of variation, mainly due to a low resolution of the available data.This work highlights how GWL variations might suggest, from days to months in advance, alterations to the geodynamic equilibrium of the Etnean region, providing evidence of the importance of groundwater monitoring and providing suggestions for future research. We envisage that this work will encourage the implementation of an efficient quantitative groundwater monitoring network which could reveal crucial information in the search for precursor signals