Intense magmatic degassing through the lake of Copahue volcano, 2013?2014

TAMBURELLO G; AGUSTO M; CASELLI A; TASSI F; VASELLI O; CALABRESE S; ROUWET D; CAPACCIONI B; DI NAPOLI R; CARDELLINI C; CHIODINI G; BITETTO M; BRUSCA L; BELLOMO S; AIUPPA A

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Año: 2015 vol. 120 p. 6071 - 6084

0148-0227

Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hostedwithin the summit crater of Copahue, a very active volcano on the Argentina-Chile border. Our observationswere performed using a variety of in situ and remote sensing techniques during field campaigns in March 2013,when the crater hosted an active fumarole field, and in March 2014, when an acidic volcanic lake coveredthe fumarole field. In the latter campaign, we found that 566 to 1373 t d1 of SO2 were being emitted from thelake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, wasconverted into flux of other volcanic species (H2O~ 10989 t d1, CO2~638td1, HCl~66td1, H2~3.3td1,and HBr ~ 0.05 t d1). These levels of degassing, comparable to those seen at many open-vent degassing arcvolcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue?s unusual degassing regimewas also confirmed by the chemical composition of the plume that, although issuing from a hot (65°C) lake,preserves a close-to-magmatic signature. EQ3/6 models of gas-water-rock interaction in the lake were able tomatch observed compositions and demonstrated thatmagmatic gases emitted to the atmosphere were virtuallyunaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H2O flux (10,988 t d1) suggesteda mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likelycommon to many degassing volcanic lakes worldwide.