ALBERT

Description: Villarrica is one of the most active volcanoes in Chile, has a persistent lava lake within its crater, and is presently characterized by continuous degassing and high-level seismicity. We use a multiparameter approach based on high time-resolution gas flux measurements and seismic data to characterize magmatic and tectonic processes controlling the volcanic activity. The instrumentation includes 3 ground-based NOVAC-type scanning Mini-DOAS spectrometers for the quantification of SO2 fluxes, installed at the volcano in March 2009, which are complemented with seismic data from the catalogue of the Volcanic Observatory of the Southern Andes (OVDAS in Spanish) and from the SFB 574 temporary volcanic network. During the last three years, we have detected activity variations at Villarrica occurring on several time scales, which can be related to distinct processes at depth. The monthly averages in degassing rates increased from 400 tons/d SO2 before December 2009, to about 1200 tons/d SO2 in April 2010. Superimposed on this pattern are strong pulses of seismic LP events occurring every 3 to 4 months, accompanied by peaks in degassing rates, interpreted as periodic influx of fresh magma batches to the deeper levels of the plumbing system. The degassing rates further show cyclic variations with a periodicity of 5 to 7 days. We interpret the latter variations to represent the turnover time for a conduit convection cycle of magma from a mid-crustal reservoir, where the degassing peaks correspond to the arrival of comparatively undegassed magma at shallow levels. In addition, irregular regional earthquake events are typically followed by increased degassing activity at Villarrica 2-4 days later, interpreted as due to increased bubble nucleation in the magmatic system at depth. The period of strongly increasing degassing rates between December 2009 and April 2010 encompasses the M 8.8 Maule earthquake, which occurred on February 27, 2010. However, the degassing variations show a complex pattern, including a steady increase already 3 months before the Maule earthquake. Degassing rates dropped off sharply 7 days before the earthquake, and was followed by several weeks of comparatively low degassing during the aftershock phase. At the end of March, degassing rates picked up to a factor of 3 above the pre-earthquake level culminating with a peak of 2800 tons/d SO2 at the beginning of April. The persistence of high degassing rates even two years later indicates a permanent change in the magma plumbing system. Further, the observation that the Maule earthquake rather interrupted than enhanced the trend of increased degassing requires a fundamental increase in the magma supply to Villarrica commencing months before the rupture event. We tentatively assign the increased availability of magma to pre-rupture creep in the lower crust or at mantle depths, enabling a pressure gradient for influx of magma. We suggest that such a change in the volume of incoming magma would probably have led to an eruptive cycle at a closed vent system like e.g. the neighboring Llaima volcano.

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: A high-resolution three-dimensional (3D) numerical basin model, incorporating the eastern part of the Lower Saxony Basin (LSB), the Gifhorn Trough and parts of the southern Pompeckj Block, was built to reconstruct the thermal and structural evolution of this area. The estimation and calculation of the unconventional oil and gas resource density within the Posidonia Shale source-rock unit was the main objective of this study. Incorporating organic–geochemical data for the Posidonia Shale source-rock units, such as compositional petroleum generation kinetics data, allowed a more accurate prediction of hydrocarbon potential compared to large-scale models of the area, as well as a better prediction of bulk adsorption capacity and adsorbed gas content. For the accurate calculation of oil and gas contents within the source-rock lithologies, mineralogy and physical properties of the rocks, such as compressibility, sorption capacity and porosity, are important as well as organic matter quantity, quality and thermal maturity. These properties in turn are strongly dependent on the vastly different burial/uplift histories within the LSB, Gifhorn Trough and the Pompeckj Block. The Gifhorn Trough, large parts of the Pompeckj Block and the flanks of the LSB are interesting concerning the unconventional oil potential, with current source-rock maturities between 0.65% and 1.2% vitrinite reflectance. Central parts of the LSB and small parts of the Pompeckj Block show inherent unconventional gas potential. Methane adsorption capacity is influenced by the burial/uplift history of the basin, which stresses the importance of structural and geochemical interlocking in understanding unconventional hydrocarbon systems.