PRE-ERUPTIVE GEOCHEMICAL CHANGES OF THE PETEROA VOLCANIC GASES AS PRECURSOR OF THE 2018-2019 ERUPTION

AGUSTO M; TASSI F; GARCÍA S; NOGUÉS V; LLANO J; LAMBERTI M C; CARBAJAL F

Estocolmo

Workshop; First Virtual Workshop: A new decade of volcanic gas research; 2021

CCVG

Peteroa volcano (35.240ºS, 70.570ºW, 3603 m.a.s.l.) is part of the NNE-oriented Planchón-Peteroa-Azufre Volcanic Complex (Argentina-Chile), located at the Southern Andean Volcanic Zone. Peteroa volcano is characterized by frequent phreatic and phreatomagmatic eruptions. After the 2010-2011 eruptive period, the volcano showed low degassing and seismicity activities. However, since 2017 an increase in seismic activity was observed, followed, since 2018, by increasing in gas emission from the crater area, which culminated on December 14th, 2018, when a new phreatomagmatic eruption occurred. In this study, the chemical and isotopic compositions of gases from crater emissions measured and collected between 2015 and 2018, prior and during the ongoing volcanic crisis from Peteroa volcano are presented and discussed. During the pre-eruptive period (2015-2018), the fumaroles from the summit crater showed a significant increase of the SO2/CO2 and SO2/H2S ratios, from 1.5x10-4 and 5x10-3 recorded in 2016-2017, to 4x10-2 and 4x10-1, respectively. During February-March 2018, a SO2 flux of 188(±28) tSO2/d was measured by DOAS, while the CO2/SO2 ratio of the plume, determined by PITSA, ranged from 1,44 to 1,81, providing an estimated CO2 flux of 300(±72) tCO2/d. The observed changes in fumarolic gas composition and the increased degassing activity occurred in 2015-2018 suggest an input of fluids from magma as precursor of the 2018-2019 eruption.