Response of a Hydrothermal System to Escalating Phreatic Unrest the Case of Turrialba and Irazú in Costa Rica (2007-2012)

Abstract

This study presents the first hydrogeochemical model of the hydrothermal systems of Turrialba and Irazú volcanoes in central Costa Rica, manifested as thermal springs, summit crater lakes, and fumarolic degassing at both volcanoes. Our period of observations (2007-2012) coincides with the pre- and early syn-phreatic eruption stages of Turrialba volcano that resumed volcanic unrest since 2004, after almost 140 years of quiescence. Peculiarly, the generally stable Irazú crater lake dropped its level during this reawakening of Turrialba. The isotopic composition of discharged fluids reveals the Caribbean meteoric origin; a contribution of “andesitic water” for Turrialba fumaroles up to ~50% is suggested. Four groups of thermal springs drain the northern flanks of Turrialba and Irazú volcanoes into two main rivers. Río Sucio (i.e. “dirty river”) is a major rock remover on the North flank of Irazú, mainly fed by the San Cayetano spring group. Instead, one group of thermal springs discharges towards the south of Irazú. All thermal spring waters are of SO4-type (i.e. steam heated waters), although none of the springs has a common hydrothermal end-member. A water mass budget for thermal springs results in an estimated total output flux of 187 ± 37 L/s, with 100 ± 20 L/s accounted for by the San Cayetano springs. Thermal energy release is estimated at 110 ± 22 MW (83.9 ± 16.8 MW by San Cayetano), whereas the total rock mass removal rate by chemical leaching is ~3,000 m3/y (~2,400 m3/y by San Cayetano-Río Sucio). Despite Irazú being the currently less active volcano, it is a highly efficient rock remover, which, on the long term can have effects on the stability of the volcanic edifice with potentially hazardous consequences (e.g. flank collapse, phreatic eruptions). Moreover, the vapor output flux from the Turrialba fumaroles after the onset of phreatic eruptions on 5 January 2010 showed an increase of at least ~260 L/s above pre-eruptive background fumarolic vapor fluxes. This extra vapor loss implies that the drying of the summit hydrothermal system of Turrialba could tap deeper than previously thought, and could explain the coincidental disappearance of Irazú’s crater lake in April 2010.

Physical and chemical characteristics of active sulfur flows observed at Lastarria volcano (northern Chile) in January 2019

“…Occasional visits to this volcano (only a few days every year) owing to access difficulties reduce the possibility of observing this phenomenon. Despite favorable physicochemical conditions for native sulfur formation, we believe that molten sulfur manifestations are sporadic events triggered by mechanical effects, such as the opening of new fractures or changes in host rock permeability (e.g., Rouwet et al, 2017). This sporadicity also explains the occurrence of molten sulfur only in specific sections of the fumarolic field, weakening the theory that sulfur flows are produced by the general melting of previously formed sulfur crusts owing to the heating of the fumarolic field.…”

Heat transport process associated with the 2021 eruption of Aso volcano revealed by thermal and gas monitoring

“…Recent studies have successfully captured slight thermal precursors of phreatic eruptions. However, in many cases only qualitative records of thermal activity sequences are provided, such as temperature increases in crater lakes, springs, and fumaroles (e.g., Christenson et al 2010;Rouwet et al 2021) and the geothermal anomaly area expansions (e.g., Tajima et al 2020). Several studies have attempted to quantify the heat disharge at different stages, such as the net change before and after an eruption (e.g., Ehara et al 2005;Mannen et al 2018), co-eruptive heat discharge , post-eruptive temporal change (Nakaboh et al 2003;Narita et al 2019), and rapid increases due to unrest events (e.g., Chiodini et al 2001;Behr et al 2023).…”