Sergey Senyukov

Feeding volcanoes of the Kluchevskoy group from the results of local earthquake tomography

[1]xa0We present a seismic model of the area beneath the Kluchevskoy volcano group (Kamchatka, Russia) based on the tomographic inversion of more than 66000 P and S arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations. Below a depth of 25 km beneath the Kluchevskoy volcano, we observed a very strong anomaly in the Vp/Vs ratio that reached as high as 2.2. This is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers. The upper part of this anomaly at a depth of 25–30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension, water release and/or phase transitions. In the crust, we observed regular seismicity clusters that link the mantle anomaly with the Kluchevskoy volcano and most likely indicate the paths of magma migration. Between depths of 8 and 13 km, we see several patterns of high Vp/Vs ratios, interpreted as intermediate-depth magma storages. Directly below the Kluchevskoy volcano, we observed a shallow body of high Vp/Vs, which probably represents the activated magma chamber just beneath the volcano cone, which erupted in the beginning of 2005. The existence of three levels of magma storage, based on results of local earthquake tomography, may explain the variety of the lava composition and eruption regimes in different volcanoes of the Kluchevskoy group.

Another “Great Tolbachik” Eruption?

On 27 November 2012 at 1715 local time, a focused swarm of earthquakes was interpreted as the start of a new ongoing eruption on the south flank (Tolbachinsky Dol) of Plosky Tolbachik volcano in east central Kamchatka, Russia (Figurexa01a) [Samoylenko et al., 2012]. Visual observations on 29 November showed ash shooting from two fractures as well as long, rapidly moving lava flows. Although the initial ash clouds reached 6 kilometers in height, subsequent ashfall has been limited to the area around the main vents, and no permanent settlements are in danger from advancing lava flows (the closest settlements are about 40 kilometers from the volcano). Including this eruption, six different volcanoes are presently active in Kamchatka.

Three different types of plumbing system beneath the neighboring active volcanoes of Tolbachik, Bezymianny, and Klyuchevskoy in Kamchatka

The Klyuchevskoy group of volcanoes (KGV) in Kamchatka includes three presently active volcanoes (Klyuchevskoy, Bezymianny, and Tolbachik) located close together in an area of approximately 50 × 80 km. These three volcanoes have completely different compositions and eruption styles from each other. We have analyzed new data recorded by a temporary seismic network consisting of 22 seismic stations operated within the area of Tolbachik in 2014–2015 in conjunction with the data from the permanent network and the temporary PIRE network deployed at the Bezymianny volcano in 2009. The arrival times of the P and S waves were inverted using a local earthquake tomography algorithm to derive 3-D seismic models of the crust beneath the KGV as well as accurate seismicity locations. High-resolution structures beneath the Tolbachik volcanic complex were identified for the first time in this study. The tomography results reveal three different types of feeding system for the main KGV volcanoes. The basaltic lavas of the Klyuchevskoy volcano are supplied directly from a reservoir at a depth of 25–30 km through a nearly vertical pipe-shaped conduit. The explosive Bezymianny volcano is fed through a dispersed system of crustal reservoirs where a lighter felsic material separates from the mafic component and ascends to the upper crust to form andesitic magma sources. For Tolbachik, low-viscosity volatile-saturated basalts ascend from two deep reservoirs following a system of fractures in the crust associated with the intersections of regional faults. Plain Language Summary The Klyuchevskoy group of volcanoes (KGV) in Kamchatka includes three presently active volcanoes (Klyuchevskoy, Bezymianny, and Tolbachik) located close together in an area of approximately 50 × 80 km. These three volcanoes are among the most active volcanoes in the world, and they have completely different compositions and eruption styles from each other. We have analyzed new data recorded by a temporary seismic network consisting of 22 seismic stations installed within the area of Tolbachik in 2014–2015 in harsh natural conditions. Based on these data, we have derived high-resolution structures beneath the Tolbachik volcanic complex and surrounding areas. The tomography results reveal three different types of feeding system for the main KGV volcanoes. The basaltic lavas of the Klyuchevskoy volcano are supplied directly from a reservoir at a depth of 25–30 km through a nearly vertical pipe-shaped conduit. The explosive Bezymianny volcano is fed through a dispersed system of crustal reservoirs where a lighter felsic material separates from the mafic component and ascends to the upper crust to form andesitic magma sources. For Tolbachik, low-viscosity volatile-saturated basalts ascend from two deep reservoirs following a system of fractures in the crust associated with the intersections of regional faults.