Most of the Kharchinskii and Zarechnyi products, as well as those of the Kharchinskii cinder cones, are magnesian rocks. Mineralogical data suggest that both the basaltic and the andesitic magma were rich in water (≥3-4 and >6-7 wt., respectively) and crystallized at high oxygen fugacity (2.0-2.5 orders of magnitude higher than the NNO buffer). These features, coupled with the geochemical characteristics of these basalts and andesites, indicate that they are similar to the rocks of Shiveluch, a volcano also located on the northern flank of the Northern volcanic group, but differ from the rocks of the other volcanoes of this group which are located further south. The Kharchinskii, Zarechnyi, and Shiveluch magnesian basalts differ from the rocks of the Klyuchevskoi volcano and Tolbachik lava field by their higher K, Ba, Sr and lower Ca, Sc, Yb contents at higher La/Yb, Ni/Sc, and La/Ta ratios, while their initial magmas were more hydrous and more oxidized.

The eruptive history of the Shiveluch andesite volcano included two Holocene events, during which
the volcano erupted unusual rocks: medium-potassium, amphibole-bearing magnesian basalts (7600 years ago)
and high-potassium magnesian basalts with phlogopite and amphibole (3600 years ago). The volumes of tephra
were approximately 0.1 and 0.3 km3, respectively. Some of the mineralogical and geochemical features of the
Holocene basalts were inherited by the subsequent basaltic andesites and andesites. These are similar in Mg
variation ranges of olivine, clinopyroxene, and amphibole phenocrysts, high Mg contents, and high Cr and Ni
concentrations. This and the results of mass-balance calculations do not contradict the view that the Shiveluch
volcanic rocks originated during the crystal fractionation of Holocene basalt melts. However, the other
geochemical features of the Shiveluch rocks, e.g., their similar REE contents, cast doubt on the formation of
the magnesian basaltic andesites through fractional crystallization of magnesian basalt magma and suggest that
they originated as a result of interaction between magnesian basalt magma and a depleted mantle material at a
shallow depth. At the same time, the different mineral compositions of the Holocene medium- and high-potassium
basalts and the results of mass-balance calculations indicate that their parental magmas might be produced
by the melting of different rocks.

Андезитовый вулкан Шивелуч в голоценовое время дважды извергал необычные для него породы:
амфиболсодержащие магнезиальные умереннокалиевые базальты (7600 лет назад) и магнезиаль-
ные высококалиевые базальты с флогопитом и амфиболом (3600 лет назад). Объем тефры соста-
вил примерно 0.1 и 0.3 км3 соответственно. Некоторые минералогические и геохимические особен-
ности голоценовых базальтов, например близкий диапазон вариаций магнезиальное™ вкрапленни-
ков оливина, моноклинного пироксена и амфибола, повышенная магнезиальность пород и
повышенные содержания в них Сг и Ni, наследуются андезитобазальтами и андезитами вулкана Ши-
велуч. Эти обстоятельства, а также результаты масс-балансовых расчетов не противоречат гипоте-
зе о происхождении эффузивов вулкана Шивелуч в процессе кристаллизационной дифференциации
расплавов голоценовых базальтов. Однако другие геохимические особенности рассматриваемых
пород, например близкие содержания редкоземельных элементов в них, делают маловероятной воз-
можность образования магнезиальных андезитобазальтов путем фракционной кристаллизации рас-
плава магнезиального базальта, но позволяют предполагать их формирование в процессах взаимо-
действия таких расплавов с веществом деплетированной мантии на малых глубинах. В то же время
различие в минералогическом составе голоценовых умеренно- и высококалиевых базальтов и ре-
зультаты балансовых расчетов могут служить доказательством различных источников выплавле-
ния исходных расплавов для этих пород.

The combination of geological, tephrochronological and geochemical studies is used to reconstruct the Holocene eruptive history of Ksudach volcanic massif, South Kamchatka and to trace the evolution of its magma. Ksudach is located in the frontal volcanic zone of Kamchatka. From Early Holocene till AD 240, the volcano had repetitive voluminous caldera-forming eruptions. Later they gave way to frequent moderate explosive–effusive eruptions that formed the Shtyubel' stratovolcano inside the nested calderas, and then to frequent larger explosive eruptions. Holocene eruptive products are low-K2O two pyroxene–plagioclase basaltic andesite to rhyodacite. Mineralogical, geochemical and isotopic data suggest that all the rock varieties originated as a result of fractionation of an initial mafic melt, with insignificant contamination and assimilation. Intensive mixing of the fractionating melts prior to, and during the course of the eruptions, is ubiquitous. The eruptions might have been triggered by repetitive injections of new mafic melt into the silicic chamber. Crystallization of the andesitic and rhyodacitic melts is estimated to have occurred at temperatures of 970–1010°C and 890–910°C, respectively, PH2O 1.5–2.0 kbar and fO2 close to the NNO buffer. According to the experimental data, such PH2O corresponds to 4.5%–5.5% of water in the melt, that is close to the content of water in the silicic hornblende-bearing magmas of the rear zone of the Kuril–Kamchatka arc. Hence, we suggest that the transition from pyroxene phenocryst associations of the frontal zone to the hornblende-bearing ones of the rear zone might be interpreted as reflecting higher temperatures of crystallization of the melts from the frontal zone rather than increasing water content in the rear zone magmas.

A large tectonic earthquake occurred on Kamchatka peninsular on New Year's Day of 1996 along a SW–NE trending fracture system. Just two days after the earthquake and at a distance of about 10–20 km to the north, a simultaneous eruption of two separate volcanoes followed. These were Karymsky Volcano and Akademia Nauk Volcano, the latter having its first eruption in historical records. In this paper I use numerical models in order to elaborate the static stress transfer between the earthquake and the volcanic system during the sequence that culminated in the January 1996 volcano-tectonic events. The models were designed to consider (i) the geodetically identified pre-eruptive period of doming in order to calculate stress changes at the nearby SW–NE trending fracture zone, and (ii) the January 1996 Mw 7.1 earthquake in order to calculate the dilatation and stress changes at the magma plumbing system. The results suggest that stress changes related to year-long inflation under the volcanic centers increased the Coulomb failure stress at the active faults and thus encouraged the earthquake. The earthquake, in turn, prompted dilatation at the magmatic system together with extensional normal stress at intruding N–S trending dikes. Also, field measurements confirmed the presence of N–S oriented fractures above the dike. Unclamping of the N–S oriented fractures allowed magma to propagate and eventually to trigger the twin-eruption at the volcanoes Karymsky and Akademia Nauk. These findings imply that successful hazard evaluations at volcanoes elsewhere require consideration of the seismo-tectonic framework and large earthquake cycles.

The remote sub-arctic wilderness of Kamchatka contains a line of active volcanoes above the Pacific Ocean plate subduction zone. This guide is based on the itinerary of the 1999 GA excursion to sites around Petropavlovsk. Descriptions cover the Uzon caldera and its Valley of Geysers, and the volcanoes of Avacha, Karimsky, Gorely and Mutnovsky.

Abstract For the past few decades, Bezymianny volcano has erupted once to twice per year. Here, I examine eight eruptive events between 2006 and 2010. This is the first time period for which proximal or broadband seismic data have been recorded at Bezymianny. Several recurring patterns are demonstrated in advance of eruptions. Eruptions are generally preceded by 12–36 h of tremor energy elevated by 2 to 3 orders of magnitude. Locatable earthquake activity is quite erratic in the days before eruptions. For eruptions of juvenile magma, however, the cumulative moment magnitude increases with the repose time since the previous eruption. Though tenuous, this relationship is statistically significant and could improve forecasts of Bezymianny eruptions. The most energetic eruptions demonstrate increasing multiplet activity in the run-up, followed by a rapid cessation at the time of eruption. When present, this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting. Very long period seismicity (> 20 s periods) accompanies some eruptions. These tend to be the same short-lived high-energy eruptions that exhibit multiplet precursors. Four eruptions are examined in detail to illustrate the variety in eruption mechanisms. Lava dome collapses, sustained eruptions, singular paroxysmal explosions and post-explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating Bezymianny. Compared to Bezymianny's fifty-year modern history, recent eruptions have been shorter-lived and separated by longer repose times. Some evidence suggests that these eruptions may be increasingly explosive—a speculation that carries significant hazard implications. If true, however, this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors, suggesting an ability to improve the already excellent eruption forecasts available for Bezymianny.

Radiocarbon dating is widely used when studying recent volcanic activity in the Kamchatka Peninsula due to the abundance of organic matter that is associated with the volcanic deposits. Here, we present the results of 14C dating of major volcanic events within the active South Kamchatka volcanic zone. South Kamchatka includes 8 recently active volcanic centers (stratovolcanoes, calderas, and large craters) that have been erupting during the Holocene. Their tephras represent useful markers for both the southern part of the peninsula and the Northern Kurile Islands. Since these marker tephra layers facilitate stratigraphic and tephrochronological studies in this area, it was important to determine their ages. We have obtained 73 new individual 14C dates on paleosol, peat, charcoal, and wood associated with the marker tephra layers, then complemented these data with 37 earlier published dates and analyzed the resulting data set. We selected the reliable dates and then obtained average 14C ages of marker tephra layers. The details of these procedures, as well as brief descriptions of South Kamchatka Holocene eruptions and their tephra beds, are presented in the paper.