HR: 11:35h
AN: V22A-06    [Abstracts]
TI: 2006-2007 eruptions of Bezymianny volcano, Kamchatka: Petrological snapshots of the compositionally changing magma system
AU: * Izbekov, P
EM: pavel@gi.alaska.edu
AF: Alaska Volcano Observatory, Geophysical Institute, UAF, 903 Koyukuk Drive, Fairbanks, AK 99775, United States
AU: Team 2006-07, a
EM: http://www.gps.alaska.edu/PIRE/
AF: Alaska Volcano Observatory, Geophysical Institute, UAF, 903 Koyukuk Drive, Fairbanks, AK 99775, United States
AB: Bezymianny volcano, Kamchatka has been in a state of almost continuous eruptive activity since October 1955. On March 30, 1956 a sudden collapse of the edifice triggered a devastating directed blast followed by a vigorous Plinian eruption, which destroyed the summit of the volcano and formed a 1.3-km-wide crater. Within weeks the volcano started rebuilding its edifice through extrusion of the dome in the middle of the crater, intermittent collapses of the dome, and associated block-and-ash flows. By mid 70s, as the volume of the dome increased, the dome-building extrusive activity became complemented by short explosive events with pyroclastic flows and surges followed by effusions of lava flows. By late 90s the explosive eruptions became remarkably regular with 2 events per year. The change in the eruptive behavior correlates with a gradual change of the whole-rock composition of erupted magmas, which become progressively more mafic, i.e. 60.9 wt.% SiO2 in 1956 and 56.7 wt.% SiO2 in May 2006. Hornblende phenocrysts, abundant in the March 30, 1956 magma, almost disappeared in the most recent erupted products. The 1955-2007 sequence of erupted products of Bezymianny provides an excellent opportunity to investigate the response of the magma system to the collapse of the edifice. The most recent 2006-2007 products serve as snapshots of the compositionally changing magma system and may provide an opportunity to determine mineral growth rates and ages of individual phenocrysts through direct comparison of new and old erupted products. Our ongoing petrologic study and phase equilibria experiments focuses on the pre-eruptive magma conditions for individual eruptive episodes, as well as their variations since the onset of the eruptive activity at Bezymianny in 1955.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3618 Magma chamber processes (1036)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting