. Ground deformation related with geochemical changes and seismic activity at Copahue volcano, Argentina.

.- CASELLI, A. EUILLADES, P., VÉLEZ, ML., AGUSTO, M., BENGOA, C., MARTÍNEZ DÍAZ, IBAÑEZ J.,

. Reykjavik, Iceland.

Congreso; IAVCEI General Assembly; 2008

IAVCEI

In this study ground deformation perfomed by using an interferometric radar technique is related with geochemical changes and seismic activity at Copahue volcano. The Copahue volcano is located at the Southern Andean Volcanic Zone (37º 51.35’S; 71º 10.2’W) inside the Agrio square caldera. The volcano-tectonic activity of this system started in the Pliocene and during the last 250 years has experienced 12 low-magnitud phreatic and phreatomagmatic eruptions. The volcano summit is composed by nine NE-oriented craters, the active one hosting a hot (up to 42ºC) hyperacidic (pH 0.8) lake. Hot acidic springs (up to 81ºC and pH 1.5) are characterized by high SO42-, Cland F- concentrations, and seep out from the eastern summit flank of the active crater. We processed a set of 16 ascending orbit SAR images (track frame), acquired by the ENVISAT ASAR sensor. We constructed 36 differential interferograms and we identified a maximum ground deformation of 1.8 cm/y (assuming deformation rate constant over the time period). This deformation is mostly located on the volcanic edifice. Since February 2004 we observed a twofold increase on Mg/Cl ratio and a threefold increase on SO42-/Cl ratio at the springs. A possible disturbance of the system (injection of fluids into the magmatic chamber, dikes from the chamber or hydrothermal activity) could generate an increase in volume and pressure; we suggest that geochemical anomalies and ground deformation are the consequence of this process. Deformation data is being validated by source modelling; however, geochemical anomalies and the seismic activity recorded during January 2004 support our hypothesis.