The influence of earthquakes on degassing at Villarrica Volcano, Chile

Villarrica is one of the most active volcanoes in Chile and is presently characterized by continuous degassing, high-level seismicity and a persistent lava lake within its crater. Three stationary NOVAC-type scanning Mini-DOAS UV spectrometers for the quantification of SO2 fluxes were installed at the volcano in March 2009. Seismic stations used for this study include the OVDAS (Observatorio Volcanologico de los Andes del Sur) volcano monitoring network, and 7 dedicated short period and broadband seismometers that were deployed in the region for more than one year. We have registered several cases of correlation between SO2 fluxes and seismic activity (LP events). Seismic events have in several cases been followed by an increase in degassing activity. The response seems to occur on two different time scales. Regional earthquake events in 2009 and 2010, and the 2011 Araucania event which occurred on January 2 and had a magnitude of 7.1, were followed by strongly increased degassing activity at Villarrica 2-4 days later, interpreted as due to increased bubble nucleation in the magmatic system at depth. The large Maule earthquake on February 27, 2010 with a magnitude of 8.8 had little immediate effect, but was followed several weeks later by an immense increase in degassing activity of about one order of magnitude compared to the baseline level. We speculate that this was a result of changing stress fields in the lower crust and at mantle depths caused by the Maule event, possibly changing melting conditions temporarily. Numerical models based on seismic, petrologic and gas flux data are used to demonstrate the feasibility of the time-lag between seismicity and degassing. We thus aim at gaining insight into the interface between magmatic and volcano-tectonic processes, especially factors playing a role for the onset of volcanic unrest. www.ifm-geomar.de