title: Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring.
abstract: Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high-frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2-rich gas (CO2/Stotal> 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur-rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8-10 km deep, whereas the shallow magmatic gas source is at ~3-5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H2S/SO2varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO2and H2S/SO2> 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H2S/SO2< 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high-temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.
authors: Observatorio Vulcanológico y Sismológico de Costa Rica Universidad Nacional Heredia Costa Rica; Department of Earth and Planetary Sciences University of New Mexico Albuquerque New Mexico USA; Dipartimento DiSTeM Università di Palermo Palermo Italy.
authors: J Maarten
authors: JM
authors: de Moor
authors: Dipartimento DiSTeM Università di Palermo Palermo Italy; Istituto Nazionale di Geofisica e Vulcanologia Sezione di Palermo Palermo Italy.
authors: A
authors: A
authors: Aiuppa
authors: Observatorio Vulcanológico y Sismológico de Costa Rica Universidad Nacional Heredia Costa Rica.
authors: G
authors: G
authors: Avard
authors: GEOMAR Helmholtz Centre for Ocean Research Kiel Kiel Germany.
authors: H
authors: H
authors: Wehrmann
authors: New Mexico Bureau of Geology & Mineral Resources Earth and Environmental Science Department Socorro New Mexico USA.
authors: N
authors: N
authors: Dunbar
authors: Observatorio Vulcanológico y Sismológico de Costa Rica Universidad Nacional Heredia Costa Rica; School of Earth Sciences University of Bristol Bristol UK.
authors: C
authors: C
authors: Muller
authors: Dipartimento DiSTeM Università di Palermo Palermo Italy.
authors: G
authors: G
authors: Tamburello
authors: Istituto Nazionale di Geofisica e Vulcanologia Sezione di Palermo Palermo Italy.
authors: G
authors: G
authors: Giudice
authors: Istituto Nazionale di Geofisica e Vulcanologia Sezione di Palermo Palermo Italy.
authors: M
authors: M
authors: Liuzzo
authors: Dipartimento di Ingegneria Civile Design Edilizia e Ambiente Seconda Università degli Studi di Napoli Naples Italy.
authors: R
authors: R
authors: Moretti
authors: Department of Earth and Space Sciences Chalmers University of Technology Göteborg Sweden.
authors: V
authors: V
authors: Conde
authors: Department of Earth and Space Sciences Chalmers University of Technology Göteborg Sweden.
authors: B
authors: B
authors: Galle
keywords: explosive eruption; hydrothermal system; phreatic eruption; phreatomagmatic eruption; volcanic gases; volcano monitoring