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 hydrothermal systems Turrialba and Irazú volcanoes in central Costa Rica, manifested as thermal springs, summit crater lakes, fumarolic degassing at both volcanoes. Our period observations (2007–2012) coincides with pre- early syn-phreatic eruption stages volcano that resumed volcanic unrest since 2004, after almost 140 years quiescence. Peculiarly, generally stable lake dropped its level during this reawakening Turrialba. The isotopic composition all discharged fluids reveals their Caribbean meteoric origin. Four groups springs drain northern flanks into two main rivers. Río Sucio (i.e. “dirty river”) is a major rock remover on North flank Irazú, mainly fed by San Cayetano spring group. Instead, one group discharges towards south Irazú. All waters are SO 4 -type steam-heated waters), none has, however, common end-member. A water mass budget for results an estimated total output flux 187 ± 37 L/s, 100 20 L/s accounted springs. Thermal energy release 110 22 MW (83.9 16.8 Cayetano), whereas removal rate chemical leaching ~ 3000 m 3 /year (~ 2400 Cayetano-Río Sucio). Despite being currently less active volcano, it highly efficient remover, which, long term can have effects stability edifice potentially hazardous consequences (e.g. collapse, landslides, phreatic eruptions). Moreover, vapor from fumaroles onset eruptions 5 January 2010 showed increase least 260 above pre-eruptive background fluxes. extra loss implies drying system could tap deeper than previously thought, explain coincidental disappearance Irazú’s April 2010.