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

Abstract

Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of Copahue, a very active volcano on the Argentina‐Chile border. Our observations were 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 covered the fumarole field. In the latter campaign, we found that 566 to 1373 t d−1 of SO2 were being emitted from the lake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, was converted into flux of other volcanic species (H2O ~ 10989 t d−1, CO2 ~ 638 t d−1, HCl ~ 66 t d−1, H2 ~ 3.3 t d−1, and HBr ~ 0.05 t d−1). These levels of degassing, comparable to those seen at many open‐vent degassing arc volcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue's unusual degassing regime was 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 to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H2O flux (10,988 t d−1) suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likely common to many degassing volcanic lakes worldwide.

HCl degassing from extremely acidic crater lakes: preliminary results from experimental determinations and implications for geochemical monitoring

“…From this new viewpoint, the sensitivity of an active crater lake as a monitoring tool is increased, but only if we understand the processes and kinetics of why and how Cl partitions between the gas and liquid phases as the gases rise through extremely acidic water. Moreover, we assumed here that the stronger acid SO 2 stays in solution, whereas SO 2 is known to be released from acidic crater lakes (Shinohara et al 2015;Tamburello et al 2015;Gunawan et al 2016). Besides the extremely complex sulphur-speciation in crater lake environments (Delmelle & Bernard 2015; Henley 2015), how SO 2 behaves with respect to HCl in the aqueous acidic environment is not yet clear.…”

“…Nevertheless, H 2 O MultiGAS measurements in extremely humid environments still incur high uncertainties (Gunawan et al 2016). Moreover, in 2013-14 the Copahue crater lake released gases with a close-to-magmatic signature, showing that scrubbing of acidic gases was minimal, if it was occurring at all (Tamburello et al 2015). In the latter study, HCl degassing (flux) was quantified for the first time.…”

“…Extremely acidic crater lakes are hosted by volcanoes such as Poás (Costa Rica; Rowe et al 1992;Rouwet et al 2016), Kawah Ijen (Java, Indonesia; Delmelle & Bernard 1994) and Copahue (Argentina -Chile; Varekamp et al 2001;Tamburello et al 2015). The loss of HCl at the surface of a crater lake has been recognized since the 1980s at Poás (Rowe et al 1992;Rouwet et al 2014Rouwet et al , 2016, manifested as increasing SO 4 /Cl ratios in lake water with time and decreasing lake volume.…”

Split-Band Interferometry-Assisted Phase Unwrapping for the Phase Ambiguities Correction

“…The active crater is about 300 m deep and contains an acid lake created by abundant precipitations and ice melting [14]. Recent eruptions have been reported in 2000, 2012 and 2014 and the last eruption was accompanied by a degassing unrest [15]. Deformations observed over Copahue volcano using InSAR are discussed in [16,17].…”

Fluid Geochemistry and Volcanic Unrest: Dissolving the Haze in Time and Space

“…Nevertheless, recent studies quantify the gas release from the lake surface of the most acidic lakes (e.g. Aso, Copahue, Poás, Kawah Ijen; Shinohara et al 2015;Tamburello et al 2015;Capaccioni et al 2016;de Moor et al 2016;Gunawan et al 2016). Under the most extreme pH conditions (<0) HF, HCl and even SO 2 can degas freely from the lake.…”