Geochemical Characterization of Groundwater in a Volcanic System

Abstract

A geochemical investigation was undertaken at Mt. Etna Volcano to better define groundwater characteristics of its aquifers. Results indicate that the Na-Mg ± Ca-HCO3 − ± (SO4 2− or Cl −) type accounts for more than 80% of the groundwater composition in the volcano. The remaining 20% is characterized by elevated Ca 2+. Waters along coastal areas are enriched in SO4 2− or Cl − , mainly due to mixing with seawater and anthropogenic effects. The majority of the samples showed values between −4‰ to −9‰ for δ 18 O and −19‰ to −53‰ for δ 2 H, suggesting that precipitation is the predominant source of recharge to the aquifers, especially in the west of the study area. The analysis of δ 13 C and pCO2 shows values 1 to 3 times higher than those expected for waters in equilibrium with the atmosphere, suggesting a partial gas contribution from deep sources. The diffusion of gasses is likely to be controlled by tectonic structures in the volcano. The ascent of deep brines is also reflected in the CO2 enrichment (up to 2.2 bars) and enriched δ 2 H/δ 18 O compositions observed in the salt mounts of Paternò.

Hydrogeochemical temporal variations related to the recent volcanic eruption at the Cumbre Vieja Volcano, La Palma, Canary Islands

“…Increases in the pCO 2 values are directly related to changes in the CO 2 input. These anomalies found in the pCO 2 values of PH, TO, and LS could be attributed to the release of CO 2 by fresh magma that intruded into the volcano plumbing system (Bellia et al, 2015). This behavior was also observed in a thermal well located on the NE side of Stromboli (Stromboli village, Italy), in which the pCO 2 values increased by one order of magnitude, Frontiers in Earth Science frontiersin.org months before the eruption occurred in December 2002 (Inguaggiato et al, 2011).…”

“…In this study, mean values of 5.4×10 −2 , 8.1×10 −2 , and 1.1×10 −1 atm were obtained for PH, TO, and LS groundwaters, respectively (Figures 2C, 3C, 4C). In general, the samples exhibit values of 1-3 orders of magnitude higher than those expected for waters in equilibrium with the atmosphere (pCO 2 = 2.5×10 −4 atm; Bellia et al, 2015). PH, TO, and LS groundwaters show two periods where the values of pCO 2 are higher than the standard deviation (+1σ) or even higher than two times the standard deviation (+2σ) of the background population: one after the occurrence of the February 2018 seismic swarm and another during the eruptive period.…”

“…To support the chemical changes observed, Figure 9 was constructed, in which cation (Na + , K + , Ca 2+ , and Mg 2+ ) concentrations were plotted versus the HCO 3 − content. The input of deep CO 2 makes the groundwater highly reactive to the chemical weathering of the host basaltic rocks (Bellia et al, 2015). As a result of this process, HCO 3 − increases, while Na + , K + , Ca 2+ , and Mg 2+ are released into the solution.…”

Groundwater Quantity and Quality

“…Three articles [9][10][11] focused primarily on groundwater quality issues. They were from three distinctly different geographic regions in different geologic settings.…”

“…The article by Bellia et al [11] provides a thorough geochemical and isotopic description of a groundwater system in at Mt. Etna Volcano (Sicily, Italy) to better define the groundwater characteristics of its aquifers.…”