ALBERT

Description: Llaima and Villarrica are two of the most active volcanoes in the Chilean Southern Volcanic Zone and presently show contrasting types of activity. Llaima is a closed vent edifice with fumarolic activity, while Villarrica has an open vent with a lava lake, continuous degassing and tremor activity. This study is focused on characterizing the relationships between volcanic and seismic activity in the months before and after the 2010 M8.8 Maule earthquake, which was located in NNW direction from the volcanoes. Time series for tremors, long-period and volcano-tectonic events were obtained from the catalogue of the Volcanic Observatory of the Southern Andes (OVDAS) and from the SFB 574 temporary volcanic network. An increase in the amount of tremor activity, long-period events and degassing rates was observed at Villarrica weeks before the mainshock and continued at a high level also after it. This increase in activity is interpreted to be caused by enhanced magma influx at depth and may be unrelated to the Maule event. In Llaima, an increase in the volcano-tectonic activity was observed directly after the earthquake. The simultaneous post-earthquake activity at both volcanoes is consistent with a structural adjustment response. Since this enhanced activity lasted for more than a year, we suggest that it is related to a medium-term change in the static stress. Thus, the Maule earthquake may have affected both volcanoes, but did not trigger eruptions, from which we assume that none of the volcanoes were in a critical state.

Description: 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 Volcanológico 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

Description: The seismicity of Villarrica volcano is compared before and after the Maule earthquake (Mw 8.8, 2010), and the inner seismic structure is obtained through tomography.

Description: ABSTRACT FINAL ID: V44C-02 Villarrica is one of the most active volcanoes in Chile and is presently characterized by activity from open continuously degassing conduit. The twohundred meter diameter crater contains a persistent lava lake which has a diameter of approximately ten meters. For the quantification of SO2 fluxes three stationary NOVAC-type scanning Mini-DOAS UV spectrometers were installed at the volcano in March 2009. To validate the ground-based gas measurements we compared them to thermal anomalies detected by the MODVOLC algorithm which is provided by the Hawai'i Institute of Geophysics and Planetology (http://modis.higp.hawaii.edu). The MODVOLC algorithm (WRIGHT et al., 2002) uses data from the space-based Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the National Aeronautics and Space Administration’s Terra and Aqua platforms and it exhibits the possibility to monitor volcanic heat sources. Although it was not intended to detect low intensity activity from open vent degassing, we find that in the case of Villarrica the detected thermal anomalies seem to originate from the heat carried by the gas phase. Additionally we have registered correlation between SO2 fluxes and thermal activity during the whole period of our ground-based gas-monitoring. Thermal anomalies detected by the MODVOLC algorithm coincide with observed periods of increased gas flux, enabling us to estimate gas fluxes indirectly from thermal data. Wright R. et al. (2002) Remote Sensing of Environment 82, 135-155