Resumen

AGUSTO, Mariano et al. Geochemical surveillance of acidic waters from Copahue Volcano-Río Agrio System: possible application for identifying eruptive precursors. Rev. Asoc. Geol. Argent. [online]. 2012, vol.69, n.4, pp.481-495. ISSN 0004-4822.

The magmatic hydrothermal system developed at the Caviahue Copahue Volcanic Complex (CCVC) is characterized by an acidic hot lake located on the active crater of the Copahue volcano, two acid hot springs seep out from the eastern flank of the edifice that merge downstream to form the Agrio river and several hydrothermal manifestations nearby the volcanic edifice. This work present new information corresponding to samples obtained between 2003-2009 in order to characterize the different type of waters of this region and analyze temporal variation allowing the identification of anomalies that could be used for future monitoring works. According the characteristic of the different manifestations of the liquid phase present in the area of this volcanic complex, different subsystems were defined: waters from the Volcanic-Hydrologic System; Steam Heated waters; and Snow Melt waters. From the geochemical monitoring a seasonal behavior pattern was identify in upper Agrio river concentrations, sensible affected during the thermal anomaly period (AT) registered at the crater lake at mid-year 2004 showing a sharp decrease in temperature. This event was attributed to an obstruction of the fracture system that feed the crater lake due to an oversaturation and precipitation as a consequence of the arrival of hyper-concentrated deep fluids. This mechanism is considered to be responsible of the phreatic events occurred during the 90's.

Palabras clave : Volcanology; Geochemistry of fluids; Monitoring; Volcanic risk.

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