Anatomy of the Bezymianny volcano merely before an explosive eruption on 20.12.2017

Ivan Koulakov,Tatyana Stupina,René Mania,Andrey Jakovlev,Sergey Senyukov,Vesta Davydova,Sergey Z Smirnov,Natalia Bushenkova,Svetlana Ya Droznina,Ilyas Abkadyrov,Angelika Novgorodova,Thomas R Walter,Pavel Plechov

doi:10.1038/s41598-021-81498-9

Abstract

Strong explosive eruptions of volcanoes throw out mixtures of gases and ash from high-pressure underground reservoirs. Investigating these subsurface reservoirs may help to forecast and characterize an eruption. In this study, we compare seismic tomography results with remote sensing and petrology data to identify deep and subaerial manifestations of pre-eruptive processes at Bezymianny volcano in Kamchatka shortly before its violent explosion on December 20, 2017. Based on camera networks we identify precursory rockfalls, and based on satellite radar data we find pre-eruptive summit inflation. Our seismic network recorded the P and S wave data from over 500 local earthquakes used to invert for a 3D seismic velocity distribution beneath Bezymianny illuminating its eruptive state days before the eruption. The derived tomography model, in conjunction with the presence of the high-temperature-stable SiO2 polymorph Tridymite in juvenile rock samples , allowed us to infer the coexistence of magma and gas reservoirs revealed as anomalies of low (1.5) and high (2.0) Vp/Vs ratios, respectively, located at depths of 2–3 km and only 2 km apart. The reservoirs both control the current eruptive activity: while the magma reservoir is responsible for episodic dome growth and lava flow emplacements, the spatially separated gas reservoir may control short but powerful explosive eruptions of Bezymianny.

Highlights

Strong explosive eruptions of volcanoes throw out mixtures of gases and ash from high-pressure underground reservoirs
Based on elevated rockfall activity in parts associated with exponentially increased seismicity rates, this event was anticipated by the Kamchatka Branch of Geophysical Survey (KBGS), which issued alert documents two days prior to the e ruption[27]
From the continuous seismograms recorded by this temporary network and the permanent seismic stations of KBGS, we identified the 523 strongest volcano-tectonic earthquakes located in the vicinity of Bezymianny

Summary

Introduction

Strong explosive eruptions of volcanoes throw out mixtures of gases and ash from high-pressure underground reservoirs. One of the most widely used concepts for eruption monitoring and early warning is based on the assumed presence of magma reservoirs in the upper crust (up to 5 km depth), causing localized inflation and characteristic pre-eruptive changes in s eismicity[4,5] In this context, it is key to understand the physical mechanisms behind the observed phenomena in order to reveal the actual processes taking place inside the volcano prior to eruptions. The preparation phase of this eruption by means of local and regional seismic stations, satellite radar imaging, time-lapse monitoring cameras, and petrological investigations from post-eruptive sampling of fresh eruptive products Integrating all these data enables us to develop a comprehensive model of the volcano’s interior, showing the state of the plumbing system during only a few days before the large eruption. Visual signatures of the forthcoming eruption, such as rock falls and elevated degassing, can be examined by three time-lapse cameras installed by us at the vicinity of Bezymianny (Fig. 2)

Methods

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Discussion

Conclusion