Eruption dynamics of the 22-23 April 2015 Calbuco volcano (Southern Chile): analyses of tephra fall deposits.

ROMERO J.; MORGAVI D.; ARZILLI F.; DAGA R.; - CASELLI, A.T.; RECKZIEGEL F.; VIRAMONTE J.; DÍAZ ALVARADO J.

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 317 p. 15 - 29

0377-0273

After 54 years since its last major eruption in 1961, Calbuco Volcano (Ensenada, Southern Chile) reawakenedwith few hours of warning on 22 April 2015 at 18:05 local time. The main explosive eruption consisted of twoeruption pulses (lasting ~1.5 and 6 h each one) on 22 and 23 April, producing stratospheric (N15 km height)eruption columns. The erupted materials correspond to porphyritic basaltic andesite (~55 wt.% of SiO2). Thetephra fall affected mainly the area northeast of the volcano and the finest ash was deposited over SouthernChile 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 showfield observationsthat have been made 5?470 km downwind and distinguish five layers (Layers A, B, B1, C and D) representingdifferent stages of the eruption evolution: eruption onset (Layer A; pulse 1), followed by the first paroxysmalevent (Layer B; pulse 1), in some places interbedded by layer B1, tentatively representing the sedimentation ofa secondary plume during the end of pulse 1. We recognized a second paroxysm (Layer C; pulse 2) followedby the waning of the eruption (Layer D; pulse 2). The total calculated bulk tephra fall deposit volume is0.27 ± 0.007 km3 (0.11?0.13 km3 dense rock equivalent), 38% of which was erupted during the first phaseand 62% during the second pulse. This eruption was a magnitude 4.45 event (VEI 4 eruption) of subPlinian type.