KUDRIAVY volcano on Iturup island in the Kuril arc is an active calc-alkaline volcano. It has not erupted this century; its current volcanic activity is characterized by hot (up to 910oC) gas jets which have been stable for at least 30 years. The composition of the gaseous emissions is typical of high-temperature fumaroles, but we report here the discovery of unusual subsurface sublimates associated with one gas jet—a sulphide mineral containing rhenium as the only cation. To our knowledge, this is the first reported occurrence of a pure rhenium mineral. The concentration of rhen-ium in the fumarole gas is only 2–10 p.p.b., so the condensation of pure rhenium sulphide from this gas requires both enrichment of rhenium by eight orders of magnitude and remarkable selectivity. Rhenium is generally believed to exist in only trace amounts at the Earth's surface, but our findings demonstrate that it can be readily mobilized, dispersed and concentrated by degassing magmas.

A high-temperature (up to 940°C) fumarolic activity at Kudriavy volcano had been studied during 1990–1999. The maximum gas temperatures of the fumaroles were measured in 1992 as 940°C, then gradually decreased with time and reached to 907°C in 1999. Gas composition of the high-temperature fumarole became enriched in H2O and depleted in other gas components, in particular in CO2. Hydrogen isotopic compositions of the high-temperature fumarolic gases were gradually depleted in deuterium. The gradual and continuous decrease in temperature and changes in gas composition observed during the last 10-year suggest that a magmatic melt have been degassing in a relatively steady-state manner from a single magma chamber. The detail investigations in 1998 and 1999 revealed short-term changes in gas composition characterized by sporadic increases in H2, CO2, and Stotal after intense precipitations. Small-scale eruptions occurred on October 7, 1999 at the summit. The ratios of major gas components (C/S, C/Cl, S/Cl, C/F, S/F, and Cl/F) significantly increased just prior to the eruption. The eruption at the Kudriavy volcano in 1999 was likely a phreatic eruption as a result of the intense precipitations after unusually long dry period. Meteoric water penetrated into the hot zone of volcano edifice and rapidly boiled causing the eruption.

We present the results of time-dependent local earthquake tomography for the Kluchevskoy group of volcanoes in Kamchatka, Russia. We consider the time period from 1999 to 2009, which covers several stages of activity of Kluchevskoy and Bezymianny volcanoes. The results are supported by synthetic tests that recover a common 3D model based on data corresponding to different time windows. Throughout the period, we observe a robust feature below 25 km depth with anomalously high Vp/Vs values (up to 2.2). We interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust. This mantle channel directly or indirectly determines the activity of all volcanoes of the Kluchevskoy group. In the crust, we model complex structure that varies over time. During the pre-eruptive period, we detected two levels of potential magma storage: one in the middle crust at 10–12 km depth and one close to the surface just below Kluchevskoy volcano. In 2005, a year of powerful eruptions of Kluchevskoy and Besymiyanny volcanoes, we observe a general increase in Vp/Vs throughout the crust. In the relaxation period following the eruption, the Vp/Vs values are generally low, and no strong anomalous zones in the crust are observed. We propose that very rapid variations in Vp/Vs are most likely due to abrupt changes in the stress and deformation states, which cause fracturing and the active transport of fluids. These fluids drive more fracturing in a positive feedback system that ultimately leads to eruption. We envision the magma reservoirs beneath the Kluchevskoy group as sponge-structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system.

Avacha group includes two active and potentially dangerous volcanoes, Avachinsky and Koryaksky, located close to Petropavlovsk-Kamchatsky, the main city of Kamchatka. We present the results of two independent seismic studies of shallow crustal structures beneath the Avacha group based on passive and active source observations. The first study is based on the analysis of continuous recording by 11 seismic stations installed over the Avacha group in 2012 and 7 permanent stations in the same region. We present a series of 2D Rayleigh-wave group velocity maps based on correlation of ambient noise, that were then converted into 3D distribution of shear wave velocity. The second work was based on the reprocessing of an active source deep seismic sounding profile across the Avachinsky volcano that was shot in 1982–1984. We made the analysis of travel times of refracted waves using a 2D tomography inversion. The resulting seismic models appear to be consistent with each other and show clear low-velocity zone to the SW of the Avachinsky volcano and high velocity structures to NE. These observations also agree with the existing gravity and magnetotelluric measurements. Based on the obtained seismic models we identify two large buried calderas and large lava flows that are thought to be related to a series of large eruption episodes of Avachinsky occurred within the last 30,000 years.

Abstract A new fissure eruption began on 27 November 2012 on the southern slope of Plosky Tolbachik volcano, which is located in central Kamchatka, Russia, and is part of the Klyuchevskoy volcano group. We analyzed the displacement of the earth surface and the seismicity during several months before the eruption onset. According to seismic and GPS data the eruption was preceded by about 4–5 months (July–November 2012) of synchronous crustal deformation and seismicity. The seismic anomaly comprises low energy level seismicity (mainly M = 1.2–2.3) under Plosky Tolbachik volcano at a depth of less than 5 km. In the 2–3 weeks immediately preceding the eruption the rate of seismicity and the amount of radiated seismic energy exceeded the long-term average values (2000–2011) by more than 40 times. The deformation anomaly was recorded by displacement of the GPS points at distances from 20 to 60 km to the north of Tolbachik. The principal axis of the compressive strain was approximately directed towards the Tolbachik eruption site. The permanent GPS network detected radial compression and tangential stretching. The compressive strain reached about 10− 7 prior to eruption onset. The comparable duration of seismic and deformation anomalies (~ 4–5 months before the eruption) is consistent with a common origin, connected to magma rising from depth, and is interpreted as indicating that they were medium-term precursors to the eruption. Data recorded during this unrest episode of the Tolbachik volcanic zone will contribute to understanding of the reawakening of volcanic activity in this region and others worldwide with similar characteristics.

Clusters of small-volume volcanoes that individually may be defined as monogenetic, but have interlinked and
interconnected plumbing systems, are used to be categorized as monogenetic volcanic fields (MVF).We argue
that such volcanic clusters should be distinguished as separate type of volcanism, intermediate between monogenetic and polygenetic. The magma plumbing system structure of the MVF (its complexity and polymagmatic
character) is the key argument for the potential separation of themin a classification. To avoid confusion caused by geneticmeaning of the used words we suggest using a term “areal volcanism” or “areal volcanic fields” (AVF instead of MVF) as defining this special type of volcanic activity. Herewe provide a reviewof themain characteristic features of one of the largest Holocene AVF, which is active now – the Tolbachik field of cinder cones in the southern part of Klyuchevskaya volcano group (Kamchatka), known in the literature as Tolbachinsky Dol. This paper is focused on the research of magma plumbing system. We consider structural,morphological, geological, geochemical and petrological data on the erupted basalts and their genesis. Specially planned seismic experiments made in 2010–2015 (seismic tomography and microseismic sounding) allowedmodeling of the principal elements of the magma plumbing system of Tolbachik AVF. Analysis of the investigations made in this area shows that Tolbachik AVF has a complex, dynamic, variable magmatic feeding system, which can be visualized as a superposition of subvertical and sublateral magma conduits. The contrast composition of the erupted rocks is caused by their different, although genetically connected, magma sources and mixing processes. One of the long-lived eruptive centers of Tolbachik AVF is Plosky Tolbachik stratovolcano, which lost its independent activity and was captured by Tolbachik AVF in Holocene. The AVF formed rejuvenated volcanism using the feeding system of the stratovolcano like an “old anthill”. The magma plumbing system characteristics of Tolbachinsky Dol strongly support the idea of separation of AVF from monogenetic volcanism type in the classification.

Kamchatka Peninsula is one of the most active volcanic regions in the world. Many Holocene explosive eruptions have resulted in widespread dispersal of tephra-fall
deposits. The largest layers have been mapped and dated by the 14C method. The tephra provide valuable stratigraphic markers that constrain the age of many geological
events (e.g. volcanic eruptions, palaeotsunamis, faulting, and so on). This is the first systematic attempt to use electron microprobe (EMP) analyses of glass to characterize
individual tephra deposits in Kamchatka. Eighty-nine glass samples erupted from 11 volcanoes, representing 27 well-identified Holocene key-marker tephra layers, were analysed. The glass is rhyolitic in 21 tephra, dacitic in two, and multimodal in three.
Two tephra are mixed with glass compositions ranging from andesite/dacite to rhyolite. Tephra from the 11 eruptive centres are distinguished by their glass K2O,
CaO, and FeO contents. In some cases, individual tephra from volcanoes with multiple eruptions cannot be differentiated. Trace element compositions of 64 representative
bulk tephra samples erupted from 10 volcanoes were analysed by instrumental neutron activation analysis (INAA) as a pilot study to further refine the geochemical haracteristics; tephra from these volcanoes can be characterized using Cr and Th contents and La/Yb ratios.
Unidentified tephra collected at the islands of Karaginsky (3), Bering (11), and Attu (5) as well as Uka Bay (1) were correlated to known eruptions. Glass compositions and
trace element data from bulk tephra samples show that the Karaginsky Island and Uka Bay tephra were all erupted from the Shiveluch volcano. The 11 Bering Island tephra
are correlated to Kamchatka eruptions. Five tephra from Attu Island in the Aleutians are tentatively correlated with eruptions from the Avachinsky and Shiveluch volcanoes.