Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring
Journal article, 2016

Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San Jose. 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/S-total>4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2weeks before eruptions, which are accompanied by shallowly derived sulfur-rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is similar to 8-10km deep, whereas the shallow magmatic gas source is at similar to 3-5km. 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/SO2 varies 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 (>3000T/d SO2 and 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.

phreatomagmatic eruption



volcanic gases

volcano monitoring

magmatic-hydrothermal system


explosive eruption


phreatic eruption


mount st-helens

fluid geochemistry


J. M. De Moor

University of New Mexico

National University Costa Rica

University of Palermo

A. Aiuppa

Istituto Nazionale di Geofisica e Vulcanologia

University of Palermo

G. Avard

National University Costa Rica

H. Wehrmann

GEOMAR - Helmholtz Zentrum für Ozeanforschung Kiel

N. Dunbar

New Mexico Bureau of Geology and Mineral Resources

C. Muller

National University Costa Rica

University of Bristol

G. Tamburello

University of Palermo

G. Giudice

Istituto Nazionale di Geofisica e Vulcanologia

M. Liuzzo

Istituto Nazionale di Geofisica e Vulcanologia

R. Moretti

Università degli Studi della Campania Luigi Vanvitelli

Alexander Vladimir Conde Jacobo

Chalmers, Earth and Space Sciences, Optical Remote Sensing

Bo Galle

Chalmers, Earth and Space Sciences, Optical Remote Sensing

Journal of Geophysical Research

01480227 (ISSN) 21562202 (eISSN)

Vol. 121 8 5761-5775

Subject Categories

Earth and Related Environmental Sciences



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