ALBERT

Description: This paper shows the results of secondary lahar modelling in Villa La Angostura town (Neuquén-Argentina) based on the Two-Phase-Titan modelling computer code, which aimed to provide decision makers a useful tool to assess lahar hazard during the 2011 Puyehue-Cordón Caulle Volcanic Complex eruption. Possible occurrence of secondary lahars that could reach the city was analized. The performance of the Two-Phase-Titan model using 15 m resolution DEMs developed from optical satellite images and from radar satellite images was evaluated. The output of these modellings showed inconsistencies that, based on field observations, were attributed to bad adjustment of DEMs to real topography. Further testing of results using more accurate radar based 10 m DEM, proved more realistic predictions. The procedure allowed to simulate the path of flows from Florencia, Las Piedritas and Colorado creeks, which are the most influencing streams in Villa La Angostura. The output of the modelling is a valuable tool for city planning and risk management especially considering the glacial geomorphology features of the region, the strong urban development growth and the land occupation tendencies observed in last decade in Villa La Angostura and its surroundings.

Description: This paper presents the results of lahar modelling in the town of Villa La Angostura (Neuquén-Argentina) based on the Two-Phase-Titan modelling computer code. The purpose of this exercise is to provide decision makers with a useful tool to assess lahar hazard during the 2011 Puyehue-Cordón Caulle Volcanic Complex eruption. The possible occurrence of lahars mobilized from recent ash falls that could reach the city was analysed. The performance of the Two-Phase-Titan model using 15 m resolution digital elevation models (DEMs) developed from optical satellite images and from radar satellite images was evaluated. The output of these modellings showed inconsistencies that, based on field observations, were attributed to bad adjustment of the DEMs to real topography. Further testing of results using more accurate radar-based 10 m DEM, provided more realistic predictions. This procedure allowed us to simulate the path of flows from Florencia, Las Piedritas and Colorado creeks, which are the most hazardous streams for debris flows in Villa La Angostura. The output of the modelling is a valuable tool for city planning and risk management especially considering the glacial geomorphic features of the region, the strong urban development growth and the land occupation that has occurred in the last decade in Villa La Angostura and its surroundings.

Description: We model the transport and subsequent deposition of ash from Chaitén volcano, Chile, during the first week of May 2008. The simulation couples the Weather Research and Forecasting (WRF) meteorological model with the FALL3D dispersion model. We only use semi-quantitative volcanological inputs based on the first eruption reports. We consider two different run types based on forecasted and hindcasted meteorological conditions. The first simulation type can be regarded as a syn-eruptive operational forecast for the 2–8 May period. We predict the evolution of the ash cloud position, the concentration of ash on air, the expected deposit thickness, and the ash accumulation rates at different localities. The comparison of model results with observed cloud arrival times and satellite images shows the goodness of the combined WRF+FALL3D forecast system and points out the feasibility of combining these two models for short-term forecast of volcanic clouds and ash fallout.

Description: The spatial distribution of some major and trace element and isotopic characteristics of backarc Plio-Quaternary basaltic to high-Mg andesitic (51% to 58% SiO2) lavas in the southern Puna (24°S to 27°S) of the Central Andean Volcanic Zone (CVZ) reflect varying continental lithospheric thickness and the thermal state of the underlying mantle wedge and subducting plate. These lavas erupted from small cones and fissures associated with faults related to a change in the regional stress system in the southern Puna at ≈ 2 to 3 Ma. Three geochemical groups are recognized: (1) a relatively high volume intraplate group (high K; La/Ta ratio 〈25) that occurs over a thin continental lithosphere above a gap in the modern seismic zone and represents the highest percentage of mantle partial melt, (2) an intermediate volume, high-K calc-alkaline group ( La/Ta ratio 〉25) that occurs over intermediate thickness lithosphere on the margins of the seismic gap and behind the main CVZ and represents an intermediate percentage of mantle partial melt, and (3) a small-volume shoshonitic group (very high K) that occurs over relatively thick continental lithosphere in the northeast Puna and Altiplano and represents a very small percentage of mantle partial melt. Mantle-generated characteristics of these lavas are partially overprinted by mixing with melts of the overlying thickened crust as shown by the presence of quartz and feldspar xenocrysts, negative Eu anomalies (Eu/Eu 〈 0.90; most 〈 0.80), and radiogenic Sr (〉 0.7055) and Pb and nonradiogenic Nd ( εNd 〈 −0.4) isotopic ratios. Mixing calculations show that the lavas generally contain more than 20% to 25% crustal melt. The eruption of the intraplate group mafic lavas, the change in regional stress orientation, and the high elevation of the southern Puna are suggested to be the result of the late Pliocene mechanical delamination of a block (or blocks) of continental lithosphere (mantle and possibly lowermost crust). The loss of this lithosphere resulted in an influx of asthenosphere that caused heating of the subducting slab and yielded intraplate basic magmas that produced extensive melting at the base of the thickened crust. Heating of the subducting slab led to formation of the seismic gap and trenchward depletion of the slab component. Backarc calc-alkaline group lavas erupted on the margins of this delaminated block, whereas shoshonitic group lavas erupted over a zone of relatively thick nondelaminated lithosphere to the north.