Monitoring Hydrothermal Activity Using Major and Trace Elements in Low-Temperature Fumarolic Condensates: The Case of La Soufriere de Guadeloupe Volcano

Abstract

At the hydrothermal stage, volcanoes are affected by internal and external processes that control their fumarolic and eruptive activity. Monitoring hydrothermal activity is challenging given the diverse nature of the processes accounting for deeper magmatic and shallow hydrothermal sources. A better understanding of these processes has commonly been achieved by combining geochemical and geophysical techniques. However, existing geochemical techniques only include the surveillance of major gas components in fumarolic emissions or major ions in cold/thermal springs. This work presents a long-term (2017–2021) surveillance of major and trace elements in fumarolic condensates from the Cratère Sud vent, a low-temperature steam-rich emission from the La Soufriere de Guadeloupe volcano. This fumarole presented a fluctuating performance, offering a unique opportunity to reveal the behavior of major and trace elements, as well as the physicochemical processes affecting magmatic and hydrothermal sources. Time-series analyses allowed for the identification of pH-related chemical fluctuations associated with (1) variable inputs of deep magmatic components at the root of the hydrothermal system, (2) pressurization episodes of the hydrothermal system with increasing fluid–rock interaction, acid gas scrubbing, and vapor scavenging of metals, and (3) the decreased hydrothermal activity, decreasing scrubbing efficiency. Variations in the volatile content (e.g., S, Sb, B, Cl, Bi, Zn, Mo, Br, Cd, Ag, Cu, and Pb), the amount of leached rock-related elements (e.g., Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Rb, Sr, Y, Cs, Ba, REEs, and U), and variations in the concentration of Cl and S alone, are postulated as key parameters to monitor volcanic–hydrothermal systems in unrest, such as La Soufriere. Our results demonstrate that monitoring using condensates is a useful geochemical technique, complementing conventional methods, such as “Giggenbach” soda flasks or the so-called Multigas.

Hydrogeochemistry of trace and rare earth elements in the Caviahue-Copahue Volcanic Complex

“…The principal source of trace elements in natural water is water-rock interaction (Baes and Mesmer, 1976;Stumm and Morgan, 1996). Nevertheless, in volcanic environments, the contribution from volcanic gases to waters can be considerable, especially for elements like As, B, Cu, Pb, Sb, Tl, Mo, and Zn (Aiuppa et al, 2000a;Calabrese et al, 2011;Scholtysic and Canil, 2018;Inostroza et al, 2023).…”

Volatile emissions from past eruptions at La Soufrière de Guadeloupe (Lesser Antilles): insights into degassing processes and atmospheric impacts

“…La Soufrière de Guadeloupe (hereby referred to as La Soufrière) in the Lesser Antilles has been experiencing increasing unrest since 1992; the unrest reached a peak in 2018 when an earthquake was felt by the population (Moretti et al, 2020a). This volcano has a well-developed hydrothermal system in which deep gases re-equilibrate and mix with groundwaters (Brombach et al, 2000;Allard et al, 2014;Villemant et al, 2014;Tamburello et al, 2019;Moretti et al, 2020a;Moretti et al, 2020b;Moretti et al, 2021;Inostroza et al, 2022a;Inostroza et al, 2022b;Moune et al, 2022). The hydrothermal system screens the actual input of volatile components from the magma beneath and makes our understanding of magma behaviour at this system difficult.…”