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.

sulfur-dioxide

phreatomagmatic eruption

volcanic gases

volcano monitoring

mount st-helens

magmatic-hydrothermal system

insights

fluid geochemistry

precursors

explosive eruption

phreatic eruption

mantle

nicaragua

Author

J. M. De Moor

University of Palermo

University of New Mexico

National University Costa Rica

A. Aiuppa

National Institute of Geophysics and Volcanology

University of Palermo

G. Avard

National University Costa Rica

H. Wehrmann

Helmholtz

N. Dunbar

New Mexico Bureau of Geology and Mineral Resources

C. Muller

University of Bristol

National University Costa Rica

G. Tamburello

University of Palermo

G. Giudice

National Institute of Geophysics and Volcanology

M. Liuzzo

National Institute of Geophysics and Volcanology

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

DOI

10.1002/2016jb013150

More information

Latest update

9/15/2020