Abstract A large dike intrusion and fissure eruption lasting 9 months began on November 27, 2013, beneath the south flank of Tolbachik Volcano, Kamchatka, Russia. The eruption was the most recent at Tolbachik since the Great Tolbachik Eruption from 1975 to 1976. The 2012 eruption was preceded by more than 6 months of seismicity that clustered beneath the east flank of the volcano along a NW–SE trend. Seismicity increased dramatically before the eruption, with propagation of the seismicity from the central volcano conduit in the final hours. We use interferometric synthetic aperture radar (InSAR) to compute relative displacement images (interferograms) for {SAR} data pairs spanning the eruption. We use satellite {SAR} data from the Canadian Space Agency's RADARSAT-2 and from the Italian Space Agency's COSMO-SkyMed missions. Data are modeled first through a Markov Chain Monte Carlo solution for a single tensile dislocation (dike). We then use a boundary element method that includes topography to model a distributed dike-opening model. We find the best-fitting dike dips 80° to the {WNW} with maximum opening of 6–8 m, localized in the near surface and more broadly distributed in distinct regions up to 3 km beneath the surface, which varies from 1 to 2 km elevation for the eruptive fissures. The distribution of dike opening and its correspondence with co-diking seismicity suggests that the dike propagated radially from Tolbachik's central conduit.

During the 2012-2013 we have measured SO2 on Kamchatka volcanoes (Gorely, Mutnovsky, Kizimen, Tolbachik, Karymsky, Avachinsky) using DOAS (differential optical absorption spectroscopy). Mobile-DOAS, on a base of USB2000+, has been used as an instrument. The goal of this work was to estimate SO2 emission by Kamchatka volcanoes with the different types of activity. Mutnovsky and Avachinsky during the measurements period passively degassed with SO2 emission ~ 480 t/d and 210 t/d, respectively. Gorely volcano was very active, with intensive vapor-gas activity with gas discharge rate 800-1200 t/d. During the measurements at Karymsky volcano there were relatively weak explosive events (ash plum rose up to 0.5 km above the crater) with 5-10 minutes periodicity. For this time, SO2 discharge rate was ~350-400 t/d. Due to the remoteness and difficulties for accessibility of Kizimen volcano, the measurements were done only once – on October 15th, 2012. 5 traverses have been done above the gas plume. SO2 emission was ~ 700 t/d. On Tolbachik fissure eruption we have measured SO2 emission repeatedly from January until August 2013. The intensive effusion of the lava flows (basaltic andesite by composition) and frequent explosions in the crater of the cinder cone were characteristic features of this eruption. The measured gas emission was from ~1500-2200 t/d in January until 600-800 t/d in August 2013. All measurements were made not permanently, but to the extent possible. Therefore, it is difficult to make detailed conclusions on the SO2 emission on these volcanoes. Nevertheless, this research may become a starting point for the development of the system of the constant monitoring of volcanic gases emission by the active volcanoes of Kamchatka.

Estimation of the sulfur dioxide emission by Kamchatka volcanoes using differential optical absorption spectroscopy.

Fissure eruption on the slope of Plosky Tolbachik volcano continued from November 27th, 2012 until September
2013. It was named as The Institute of Volcanology and Seismology 50th Anniversary Fissure Tolbachik Eruption.
The eruption started from the 5 km-long fissure opening and continued with the intensive lava effusion from it.
During the first two days of eruption the length of the lava flows was 9 km, and lava covered the area of 14.4
km2 (Gordeev et al., 2013). Lava discharge rate at this period was about 400 m3/sec. Two eruptive centers were
formed on the fissure – upper (Menyailov vent) and lower (Naboko vent), and lava gushed from them to the height
up to 200-300 meters. On December 1st, the Menyailov vent activity ceased, and the eruption concentrated at the
Naboko vent. Cinder cone was formed here, and lava flows effused from the base of the cone. Lava erupted from
the Menyailov vent, is different from the Naboko vent lava by higher silica content (SiO2 55.35 wt.% vs. 52.5
wt.%, respectively). That may be caused by the discharge of two levels of the magma chamber, fractionated to
a different extent. Morphologically, lava flows from the beginning of eruption until April 2013 were dominantly
aa-lava type, and from April until September 2013 pahoehoe type dominated.
For distinguishing of the dynamic of the lava flows the following methods were applied. As remote sensing methods
we used different satellite data – for specification of the area covered by lava flows, their length, temperature we
used Landsat 7 ETM+, Landsat 8, ASTER, EO-1 ALI and HYPERION. For time averaged discharge rate (TADR)
and lava flow area determination we used AVHRR data. We detected that in December 2013 lava discharge rate
varied from 120 to 40 m3/sec, and then it gradually decreased to average values 5-15 m3/sec and remained on this
level until the end of eruption. These data are confirmed by the ground-based observations, which were conducted
during the entire period of eruption. At the end of eruption in September 2013, lava flows area was about 36 km2, the maximum length of the lava flow – 15 km.

Abstract We present a reconstruction of the chronological sequence of events that took place during the first days of the 2012–2013 Tolbachik fissure eruption using petrological data and remote sensing methods. We were forced to use this approach because bad weather conditions did not allow direct observations during the first two days of the eruption. We interpreted infrared images from the scanning radiometer {VIIRS} Suomi {NPP} and correlated the output with the results of the geochemical study, including comparison of the ash, deposited at the period from 27 to 29 November, with the samples of lava and bombs erupted from the Menyailov and Naboko vents. We argue that the compositional change observed in the eruption products (the decrease of SiO2 concentration and K2O/MgO ratio, increase of MgO concentration and Mg#) started approximately 24 h after the eruption began. At this time the center of activity moved to the southern part of the fissure, where the Naboko group of vents was formed; therefore, this timeframe also characterizes the timing of the Naboko vent opening. The Naboko group of vents remained active until the end of eruption in September 2013.

In the present National Report, major results are given of research conducted by Russian scientists in 2011–2014 on the topics of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) of the International Union of Geodesy and Geophysics. Kamchatka Peninsula with its famous Klyuchevskaya Group of volcanoes is the most volcanically active area in Russia and one of the most active in the world. Majority of researches and scientific results on Volcanology and Geochemistry of the Earth’s Interior during 2011–2014 were achieved in this region including recent data on new Tolbachik fissure eruption in 2012–2013. Besides it, the scientific results on the magmatism outside Russia, which were achieved by Russian scientists, are also included in this review. Major achievements in the chemistry of the Earth, geothermy, geodynamics, geochronology and deep mantle structure are featured. The studies as for the single volcanoes as well the regional observations are outlined. The theoretical and applied efforts connected to the volcanological processes are considered. The main conclusions are illustrated by summarized figures. All the required references are given.

The early 21st century saw increased eruption activity of major volcanoes in the Northern Group of Kamchatka, namely, Sheveluch, Klyuchevskoy, Bezymianny, and the Tolbachik Fissure Zone. The growth of an extrusive dome on Sheveluch andesitic volcano has occurred, with the dome reaching a height of 600 m after 38 years of nearly uninterrupted eruption activity. An 8-year period of relative quiet was followed by ten summit eruptions and two lateral vent openings on the Klyuchevskoy basaltic volcano. Explosive–effusive eruptions were observed nearly every year on the Bezymianny andesitic volcano. A 36-year quiet period gave way to a new eruption in the Tolbachik regional fissure zone.

Abstract We report petrography, and bulk rock, mineral and glass analyses of eruptive products of the 2012–13 eruption of Tolbachik volcano, Central Kamchatka Depression, Russia. Magmas are shoshonitic in composition, with phenocrysts of olivine and plagioclase; clinopyroxene phenocrysts are scarce. Samples collected as bombs from the active vent, from liquid lava at the active lava front, and as naturally solidified “toothpaste” lava allow us to quantify changes in porosity and crystallinity that took place during 5.25 km of lava flow and during solidification. Olivine-hosted melt inclusions from rapidly-cooled, mm-size tephra have near-constant {H2O} contents (1.19 ± 0.1 wt) over a wide range of {CO2} contents (< 900 ppm), consistent with degassing. The groundmass glasses from tephras lie at the shallow end of this degassing trend with 0.3 wt {H2O} and 50 ppm CO2. The presence of small saturation, rather than shrinkage, bubbles testifies to volatile saturation at the time of entrapment. Calculated saturation pressures are 0.3 to 1.7 kbar, in agreement with the depths of earthquake swarms during November 2012 (0.6 to 7.5 km below the volcano). Melt inclusions from slowly-cooled and hot-collected lavas have {H2O} contents that are lower by an order of magnitude than tephras, despite comparable {CO2} contents. We ascribe this to diffusive {H2O} loss through olivine host crystals during cooling. The absence of shrinkage bubbles in the inclusions accounts for the lack of reduction in dissolved {CO2} (and S and Cl). Melt inclusions from tephras experienced < 3 wt post-entrapment crystallisation. Melt inclusion entrapment temperatures are around 1080 °C. Compared to magmas erupted elsewhere in the Kluchevskoy Group, the 2012–13 Tolbachik magmas appear to derive from an unusually H2O-poor and K2O-rich basaltic parent.

Late Pleistocene-Holocene volcanism in Kamchatka results from the subduction of the
Pacific Plate under the peninsula and forms three volcanic belts arranged in en echelon manner
from southeast to northwest. The cross-arc extent of recent volcanism exceeds 250 km and
is one of the widest worldwide. All the belts are dominated by mafic rocks. Eruptives with
SiO2>57% constitute ~25% of the most productive Central Kamchatka Depression belt and
~30% of the Eastern volcanic front, but <10% of the least productive Sredinny Range belt.
All the Kamchatka volcanic rocks exhibit typical arc-type signatures and are represented
by basalt-rhyolite series differing in alkalis. Typical Kamchatka arc basalts display a strong
increase in LILE, LREE and HFSE from the front to the back-arc. La/Yb and Nb/Zr increase
from the arc front to the back arc while B/Li and As, Sb, B, Cl and S concentrations decrease.
The initial mantle source below Kamchatka ranges from N-MORB-like in the volcanic front
and Central Kamchatka Depression to more enriched in the back arc. Rocks from the Central
Kamchatka Depression range in 87Sr/86Sr ratios from 0.70334 to 0.70366, but have almost
constant Nd isotopic ratios (143Nd/144Nd 0.51307–0.51312). This correlates with the highest
U/Th ratios in these rocks and suggest the highest fluid-flux in the source region.
Holocene large eruptions and eruptive histories of individual Holocene volcanoes have been
studied with the help of tephrochronology and 14C dating that permits analysis of time-space
patterns of volcanic activity, evolution of the erupted products, and volcanic hazards.

On Kamchatka, detailed geologic and geomorphologic mapping of young volcanic terrains and observations on historical eruptions reveal that landslides of various scales, from small (0.001 km3) to catastrophic (up to 20–30 km3), are widespread. Moreover, these processes are among the most effective and most rapid geomorphic agents. Of 30 recently active Kamchatka volcanoes, at least 18 have experienced sector collapses, some of them repetitively. The largest sector collapses identified so far on Kamchatka volcanoes, with volumes of 20–30 km3 of resulting debris-avalanche deposits, occurred at Shiveluch and Avachinsky volcanoes in the Late Pleistocene. During the last 10,000 yr the most voluminous sector collapses have occurred on extinct Kamen' (4–6 km3) and active Kambalny (5–10 km3) volcanoes. The largest number of repetitive debris avalanches (> 10 during just the Holocene) has occurred at Shiveluch volcano. Landslides from the volcanoes cut by ring-faults of the large collapse calderas were ubiquitous. Large failures have happened on both mafic and silicic volcanoes, mostly related to volcanic activity. Orientation of collapse craters is controlled by local tectonic stress fields rather than regional fault systems.

Specific features of some debris avalanche deposits are toreva blocks — huge almost intact fragments of volcanic edifices involved in the failure; some have been erroneously mapped as individual volcanoes. One of the largest toreva blocks is Mt. Monastyr' — a ∼ 2 km3 piece of Avachinsky Somma involved in a major sector collapse 30–40 ka BP.

Long-term forecast of sector collapses on Kliuchevskoi, Koriaksky, Young Cone of Avachinsky and some other volcanoes highlights the importance of closer studies of their structure and stability.