High frequency data acquisition of physico-chemical parameters in groundwater on Mt. Etna volcano (Italy)

Mt. Etna has long been considered one of the major sources of volcanic gases worldwide. Variations in degassing activity have been therefore considered as precious indications about the activity status of the volcanic system. Though most of the gases are released by open-conduit degassing through the summit craters, a significant part of the gases diffuses through the flanks of the volcano interacting with groundwater. Acquisition of physico-chemical parameters in groundwater for volcanic surveillance purposes started on Mt. Etna nearly 40 year ago. While in the first years only periodic sampling, generally with a monthly frequency, was made, in recent years automatic monitoring stations with higher acquisition frequency (hourly) and data transmission were implemented in several groundwater sampling sites.

Moreover, the complex geodynamic situation of the eastern flank of the volcano, with tectonic and volcano-tectonic activity and flank sliding, will also have some influence on the acquired signals at the groundwater monitoring stations.

In this framework, important results are expected from monitoring of the high-frequency oscillations of water level of aquifers, a powerful tool in studying stress and strain conditions in the crust. The present experiment will represent the first time that this portion of the spectrum of the water level signal will be explored in the attempt to recognize possible precursory patterns. Given the peculiarity of the area, we will focus on episodes of magma migration, volcano tectonic events and degassing, as recognized by ground deformation, seismicity and geochemical signals, which cause the propagation elastic energy in the aquifer and can thus produce high-frequency pressure signals. The presence on the area of a well-developed network for measurement of ground deformation will allow in fact to relate our hydrological signals to inflation, deflation of the edifice and sliding of its eastern flank.

A prototype station for measurement of high-frequency (from 0.1 to 50 Hz) variation of pore pressure with an innovative absolute pressure sensor in 2.5mm case with 24bit resolution and 0-2 or 0-4 bar range has been implemented. The station acquires also the following parameters: water temperature, pH, electric conductivity. For the necessary tests, the station will be placed soon in an abandoned well with limited anthropogenic interference in the surrounding area on the eastern flank of Mt. Etna.