Calbuco volcano (Southern Chile) Eruption 22-23 April 2015: pyroclasticfall deposits and preliminary petrological study

FABIO ARZILLI; FLORENCIA RECKZIEGEL; MIKE BURTON; DANIELE MORGAVI; ROMINA DAGA; VIRAMONTE JOSE; DIEGO PERUGINI; JORGE ROMERO; ALBERTO CASELLI; MARGHERITA POLACCI

Viena

Conferencia; European Geosciences Union General Assembly 2016; 2016

After 54 years since its last major eruption in 1961, Calbuco volcano (Ensenada, Southern Chile) reawakened withfew hours of warning on 22 April 2015 at 18:05 local time. The main explosive eruption consisted of two eruptionpulses (lasting ∼1.5 and ∼6 hours each one) on 22 and 23 April, producing stratospheric (>15 km height) eruptioncolumns. The tephra fall affected mainly the area northeast of the volcano and the finest ash was deposited overSouthern Chile and Patagonia Argentina. We studied the tephra fall deposits of both pulses in terms of stratigraphy,distribution, volume, emplacement dynamics and eruption source parameters. Here, we show field observationsmade from 5 to 470 km downwind and we distinguish five layers (Layers A, B, B1, C and D) representing differentstages of the eruption evolution. The total calculated bulk tephra fall deposit volume is 0.27±0.007 km3 (0.11-0.13km3 dense rock equivalent). The 38% of it was erupted during the first phase and 62% during the second pulse.This eruption was a magnitude 4.45 event (VEI 4 eruption) of Subplinian type. The erupted materials correspondto a porphyritic basaltic-andesite (54.40-57.2 wt. of % SiO 2 ). It produced two types of pumice clasts: high densitypumice (HDP), poorly vesiculated and crystal-rich (up to 40 % crystals by volume), and lower density pumice(LDP) characterized by a slightly lower crystallinity and higher vesicle fraction. The textures include phenocrystsin a glassy groundmass with a minor presence of microlites. The mineralogical assemblage of pumices consists ofplagioclase (Pl), orthopyroxene (Opx), clinopyroxene (Cpx), Ti-magnetite, and sanidine (Sa) as accessory mineral.