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 all the discharged fluids reveals their Caribbean meteoric origin. 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), none of the springs has, however, 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 ~ 3000 m3/year (~ 2400 m3/year 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, landslides, 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.
Highlights
Rock dissolution upon the prolonged seepage of acidic fluids from summit volcano-hydrothermal systems and crater lakes weakens the mechanical stability of a volcanicRouwet et al Earth, Planets and Space (2021) 73:142 of volcano flanks (Voight et al 1983)
The thermal spring, lake waters and Meteoric water (MW) have isotopic compositions that plot slightly left of the Global Meteoric Water Line (GMWL, Fig. 5), corresponding the local meteoric water lines of Irazú and Turrialba
2011; Muñoz-Villers et al 2012), or, alternatively, rivers at lower elevations discharge the average MW after infiltration in the volcanic edifices
Summary
Rock dissolution upon the prolonged seepage of acidic fluids from summit volcano-hydrothermal systems and crater lakes weakens the mechanical stability of a volcanicRouwet et al Earth, Planets and Space (2021) 73:142 of volcano flanks (Voight et al 1983). Turrialba, Irazú’s “twin volcano” 10 km northeast, resumed volcanic unrest in 2004, after it last erupted in 1864–1866 This unrest gradually evolved through time, as evidenced by (1) the arrival of magmatic SO2 in fumaroles in 2004 (Vaselli et al 2009), (2) an increase in 3He/4He ratios in fumaroles since 2007 (Di Piazza et al 2015; Rizzo et al 2017), (3) expansion of fumarolic fields in and outside the active crater, culminating into plume degassing since April 2007 (Martini et al 2010; Campion et al 2012; Conde et al 2014; Moussalam et al 2014), and eventually by (4) the build-up towards major phreatic eruptions on 5 January 2010, 14 January 2011, 12 January 2012 and 21 May 2013 that restructured the summit morphology by adding two new vents (González et al 2015; Alvarado et al 2016; de Moor et al 2016; Stix and de Moor 2018; Mick et al 2021). To the day of writing, Turrialba remains in intermittent eruptive activity, or unrest with occasional small eruptions
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