Geochemical Monitoring System II prototype (GMS II) installation at the “Acqua Difesa” well, within the Etna region: first data during the 1999 volcanic crisis

Abstract

The Geochemical Monitoring System II (GMS II) prototype was designed, assembled, tested and installed at the Acqua Difesa test site, near Belpasso (CT), within the Etna region, in the frame of an EC funded program named Automatic Geochemical Monitoring of Volcanoes. The easily changeable and versatile configuration of the remote station provides actual data every 10min, recording: groundwater temperature, electrical conductivity, pH, redox potential, dissolved CO2, He, atmospheric pressure and air temperature. The radon sensor was assembled despite no jet added to the remote station. An automatic sampler collects every 72h (3days) two bottles of water, acidified and not, for further laboratory analyses.The choice of the Acqua Difesa test site arises from preliminary volcanological studies, deserving special interest, i.e. for the high CO2 degassing, for the high He isotopic values, exhibiting a direct mantle signature of the volcanic gases and for the peculiar sensitivity to volcanic activity as tested by discrete monitoring in the past and confirmed by the present study.During the discussed monitoring period (October 1998–June 1999) an enhanced volcanic activity of Etna was observed; it started on July 1998 with enhanced plume degassing and, since September 1998, with periodical lava fountains as well as with episodic low-energy earthquakes and seismic swarms (Mmax=3.1 till June 1999). The activity culminated with a summit crater fracture involving a sub-terminal eruption on 04/02/1999. The summit crater fracture was not accompanied by enhanced seismicity, despite moderate seismic energy release occurring in the succeeding months. In that monitoring period, the Acqua Difesa GMS II station recorded a few geochemical anomalies, mostly in temperature, pH, CO2, electrical conductivity and Eh as well as in the concentration of some major elements trend, mostly in Mg and HCO3. The geochemical continuous and discrete data-set is discussed in comparison with the available information on the ongoing volcanic and seismic activity tentatively enhancing the comprehension of the aquifers mass–heat transport properties of the volcano during crises. The experimental observations may be defined, at present, the “forerunners” of the Etna eruptions affecting the single-out Acqua Difesa well. It is nowadays a “self consistent” site with its own response to the pre-eruptive processes, defined sensitive to the Etna aquifer modifications induced by the volcanic activity, in a recurrent way. Thus, we defined the “typical answer” of this specific test-site to the pre-eruptive processes and to the associated seismicity. Further data may modify this statement. The station prototype configuration and the results may give hints for future volcanic eruption and seismic activity forecasting.