Eruptive activity of Planchón-Peteroa volcano for period 2010-2011, Southern Andean Volcanic Zone, Chile.

GUTIERREZ F.; GONZALEZ R.; AGUILERA F,.; ROMERO J.; BENAVENTE O.; AGUSTO M.; SALTORI O.; - CASELLI, A.T.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2016 vol. 43 p. 20 - 46

0718-7092

Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. Thiseruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreaticactivity, which produced almost permanent gas/steam columns (200-800 m height over the active crater). Those columnspresented frequently scarce ash, and were interrupted by phreatic explosions that produced ash columns 1,000-3,000 mheight in the more intense periods. Eruptive plumes were transported in several directions (NW, N, NE, E and SE), butmore than half of the time the plume axis was 130-150° E, and reached a distance up to 638 km from the active crater.Tephra fall deposits identified in the NW, N, NE, E and SE flanks covered an area of 1,265 km2, thickness variable from4 m (SE border of active crater) to ~0.5 cm 36.8 km SE and ~8 km NW from active crater, respectively, correspondingto a minimum volume of 0.0088 km3. Tephra fall deposit is exclusively constituted of no juvenile fragments including:lithics fragments as main component, quartz and plagioclase crystals, some oxidized lithics, and occasional presenceof Fe oxide, and less frequently Cu minerals, as single fragments. We present new field-based measurements data ofthe geochemistry of gas/water from fumaroles and acid crater lakes, and fall deposit analysis, that integrated with theeruptive record and GOES satellite data, suggests that the eruptive period 2010-2011 has been related to an increasingof heat and mass transfer from hydrothermal-magmatic reservoirs, which would have been favoured by the formationand/or reactivation of cracks after 8.8 Mw Maule earthquake in February 2010. This process also allowed the ascent offluids from a shallow hydrothermal source, dominated by reduced species as H2S and CH4, during the entire eruptiveperiod, and the release of more oxidizing fluids from a deep magmatic reservoir, dominated by acid species as SO2,HCl and HF, increasing strongly after the end of the eruptive period, probably since October 2011. The eruptive periodwas scored with a magnitude of 3.36, corresponding to a VEI 1-2.