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

The Geochemical Monitoring System II (GMS II) prototype was designed, assem bled, 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 Autom atic Geochemical Monitoring of Volcanoes. The easily changeable and versati le configuration of the remote station provides actual data every 10 min, r ecording: groundwater temperature, electrical conductivity, pH, redox poten tial, dissolved CO2, He, atmospheric pressure and air temperature. The rado n sensor was assembled despite no jet added to the remote station. An autom atic sampler collects every 72 h (3 days) two bottles of water, acidified a nd not, for further laboratory analyses. The choice of the Acqua Difesa test sire arises from preliminary volcanolog ical studies, deserving special interest, i.e. for the high CO2 degassing, for the high lie isotopic values, exhibiting a direct mantic signature of t he volcanic gases and for the peculiar sensitivity to volcanic activity as tested by discrete monitoring in the past and confirmed by the present stud y. During the discussed monitoring period (October 1998-June 1999) an enhanced volcanic activity of Etna was observed; it started on July 1998 with enhan ced plume degassing and, since September 1998, with periodical lava fountai ns as well as with episodic low-energy earthquakes and seismic swarms (M-ma x = 3.1 till June 1999). The activity culminated with a summit crater fract ure involving a sub-terminal eruption on 04/02/1999. The summit crater frac ture was not accompanied by enhanced seismicity. despite moderate seismic e nergy release occurring in the succeeding months. In that monitoring period , the Acqua Difesa GMS II station recorded a few geochemical anomalies, mos tly in temperature, pH, CO2, electrical conductivity and Eh as well as in t he concentration of some major elements trend, mostly in Mg and HCO3. The g eochemical continuous and discrete data-set is discussed in comparison with the available information on the ongoing volcanic and seismic activity ten tatively enhancing the comprehension of the aquifers mass-heat transport pr operties 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 "sef consistent" site with i ts own response to the pre-eruptive processes, defined sensitive to the Etn a aquifer modifications induced by the volcanic activity, in a recurrent wa y. Thus, we defined the "typical answer" of this specific test-site to the pre-eruptive processes and to the associated seismicity. Further data may m odify this statement. The station prototype: configuration and the results may give hints for future volcanic eruption and seismic activity forecastin g. (C) 2000 Elsevier Science B.V. All lights reserved.