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Magma storage, pre-eruptive dynamics and timescales of the 1956 eruption of Bezymianny volcano (Kamchatka)

Léa Ostorero1,2, Caroline Martel3, Georges Boudon1, Hélène Balcone-Boissard4, Saskia Erdmann3, Daniel J. Morgan5, Alexander Belousov6, Marina Belousova6, Vesta O. Davydova7, Vasily D. Shcherbakov7, Thiebaut d'Augustin4

  • Affiliations: 1Université Paris Cité, Institut de physique du globe de Paris (IPGP), CNRS, F-75005 Paris, France; 2Department of Earth and Environmental Sciences, University of Milano‐Bicocca, Milan, Italy; 3Institut des Sciences de la Terre d'Orléans (ISTO), UMR 7327, Université d'Orléans-CNRS/INSU-BRGM, Orléans, France; 4Institut des Sciences de la Terre de Paris (ISTeP), UMR 7193, CNRS‐Sorbonne Université, Paris, France; 5Institute of Geophysics and Tectonics, School of Earth & Environment, University of Leeds, Leeds LS2 9JT, UK; 6Institute of Volcanology and Seismology, 9 Piip Boulevard, Petropavlovsk-Kamchatsky, 683006, Russia; 7Lomonosov Moscow State University, Geological Departments, Leninskii Gory, 1, 119191 Moscow, Russia 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 64

  • Programme No: 1.2.9

  • Theme 1 > Session 2

Abstract

Laterally directed blasts are explosive events following a major sector collapse of a volcano, with the potential for devastating areas of several hundred km2, due to powerful dilute and turbulent pyroclastic density currents. The catastrophic flank collapse on 30 March 1956 of Bezymianny (Kamchatka, Russia) was the climactic phase of the first historical magmatic eruption of this volcano, after 1000 years of dormancy. Magma stored in a cryptodome was depressurized by a sector collapse, generating a laterally directed blast immediately followed by pumiceous concentrated pyroclastic density currents. We infer the storage conditions of magma using sample vesicularity, amphibole destabilization rims, volatile contents in melt inclusions, microlite textures, and phase compositions. We propose a three-level magma storage characterized by a deep reservoir (> 200-350 MPa, ≥ 840 °C), a shallow reservoir (50-100 MPa, 850-900 °C) in which the pre-cryptodome magma resided and from which the post-blast pumiceous magma originated, and a subsurface cryptodome (< 25 MPa, ~900 °C) from which the blast was initiated. By combining petrological and temporal constraints from orthopyroxene, magnetite, and amphibole chronometers, we track magmatic processes over twelve years prior to the eruption, followed by magma ascent to a shallow reservoir and a heating process at least three months before the eruption. Magma was last stored in a cryptodome at least two months before the climactic phase of the eruption. Reconstructing magma dynamics on a timescale of months to years before major flank collapses and laterally directed blasts thus provides valuable information for volcanic risk mitigation.