Recent studies at Lascar Volcano, Chile: a multidisciplinary monitoring effort to understand eruptive patterns and products

J.G.VIRAMONTE, L. A. RODRIGUEZ, R. BECCHIO; S. CASTRO; I.M. WATSON; F. AGUILERA

Quito, Ecuador

Simposio; Cities on Volcanoes 4; 2006

IAVCEI

Lascar is the most active volcano in the Central Andes and has affected air traffic in Argentina and the mining activity in the Puna region through regular ash and has the potential to affect local populations, such as Talabre (15 km NW), through generation of pyroclastic density currents. A multidisciplinary project was started in 2002 to study activity using satellite ( ~100 ASTER images from 2000-2005 - used to quantify sulfur dioxide fluxes and temperatures) and ground-based techniques. Field campaingns in 2002 and 2004 have included the deployment of instruments to measure SO2 gas emissions (mini UV spectrometers), aerosol particle size distributions (sun photometers), and temperatures of the vent fumaroles (thermocouples and a Forward Looking IR radiometer). We have also started the characterization of deposits (using FTIR techniques), as part of a project to create a spectral library of Andean deposits, for improving ananlyses of satellite images. Here we present results from these studies within the context to the pre-eruptive conditions at Lascar. The most recent eruption occurred in May 4, 2005, with a column that rose to 10-11 km heights and traveled to the southeast. Very fine ashfall reached Salta, Argentina (~285 km SSE), in less than 3 hours. The grain size, shape, and composition of tht ash, together with satellite data, suggest that is was a short phreato-vulcanian eruption. A crater visit on May 25 indicated the presence of three new fumaroles a few meters from its south border, as well as the abesence of new bombs or blocks. Future work includes a systematic gas sample campaign at Lascar an other active volcanoes on the Central Volcanic Zone, as well as the processing of Landsat TM and ETM + images, with the objetive of understanding the behavoir of Lascar during the 1998-2004 period during a postulated eruptive cycle oscillation.