The second phase of field work in 2020 on the Alaid Volcano, located on Atlasov Island in the north of the Kuril Island Arc, was carried out on October 2. There was no snow in the crater at the time, and this made it possible to study the deep part of the crater and take samples of rocks and snow. The measurements of the temperature of fumarole gases showed that for the tested fumaroles it varied in the range of 35° to 95° C. Rock samples were also taken from the Svechka Rock and at Cape Shtormovoy. It was found that there is currently no water in Yuryev Creek, located in the west-northwest part of Atlasov Island. The studies carried out have made it possible to obtain new unique information, which will undoubtedly be useful to various researchers of active volcanoes in the Kuril island arc.

The paper presents the results of integrated geophysical observations of the Ebeko Volcano’s activity in late 2018 and early 2019. The instrument complex for observation was located at the Severo-Kurilsk seismic station at a distance of 7.2 km far from the volcanic crater. Three types of response in the vertical component of the electric field of the atmosphere have been distinguished during the drift of eruptive clouds from the Ebeko Volcano’s explosions, which gives evidence for various mechanisms of their occurrence. The registration of infrasonic acoustic signals in the near zone made it possible to estimate the trinitrotoluene equivalent for the strongest explosions, which was calculated to be about 100 kg of trinitrotoluene. The authors have revealed certain regularities in the dynamics of the volumetric activity of radon, associated with variations in meteorological values and hydrological features of the registration point. A long period of its activity and the proximity of the observation point to the crater give reason to suggest Ebeko Volcano to be a natural laboratory for studying the mechanisms of eruptions.

Growth of explosive activity of Ebeko volcano in April–June 2020

Klyuchevskoy volcano activity between November 2019 and June 2020

Статья посвящена исследованию генетических связей пород K–Na умеренно-щелочной серии, проявленной в строении вулканического центра Белоголовский расположенного в тыловой части Срединного хребта Камчатки. Дифференцированный ряд пород серии включает в себя трахибазальты, трахиандезиты, трахиты, комендитовые трахиты и комендиты. Проведение расчетов баланса масс и редкоэлементного моделирования показало, что кристаллизационная дифференциация является основным процессом эволюции расплавов изученного вулканического центра, при этом основным фракционирующим минералом является полевой шпат. Методом LA-ICP-MS получены редкоэлементные характеристики породообразующих минералов (Fsp, Cpx, Bt, Ap, Ol), рассчитаны коэффициенты “минерал/порода”, что позволило представить модель эволюции расплавов вулканического центра Белоголовский. Установлены генетические связи между трахиандезитами, трахитами, комендитовыми трахитами и комендитами, тогда как трахибазальты и трахиандезиты не обнаруживают прямых генетических связей.

The Kamchatka Peninsula of eastern Russia is currently one of the most volcanically active areas on Earth where a combination of > 8 cm/yr subduction convergence rate and thick continental crust generates large silicic magma chambers, reflected by abundant large calderas and caldera complexes. This study examines the largest center of silicic 4-0.5 Ma Karymshina Volcanic Complex, which includes the 25 × 15 km Karymshina caldera, the largest in Kamchatka. A series of rhyolitic tuff eruptions at 4 Ma were followed by the main eruption at 1.78 Ma and produced an estimated 800 km3 of rhyolitic ignimbrites followed by high-silica rhyolitic post-caldera extrusions. The postcaldera domes trace the 1.78 Ma right fracture and form a continuous compositional series with ignimbrites. We here present results of a geologic, petrologic, and isotopic study of the Karymshina eruptive complex, and present new Ar-Ar ages, and isotopic values of rocks for the oldest pre- 1.78 Ma caldera ignimbrites and intrusions, which include a diversity of compositions from basalts to rhyolites. Temporal trends in δ18O, 87Sr/86Sr, and 144Nd/143Nd indicate values comparable to neighboring volcanoes, increase in homogeneity, and temporal increase in mantle-derived Sr and Nd with increasing differentiation over the last 4 million years. Data are consistent with a batholithic scale magma chamber formed by primarily fractional crystallization of mantle derived composition and assimilation of Cretaceous and younger crust, driven by basaltic volcanism and mantle delaminations. All rocks have 35–45% quartz, plagioclase, biotite, and amphibole phenocrysts. Rhyolite-MELTS crystallization models favor shallow (2 kbar) differentiation conditions and varying quantities of assimilated amphibolite partial melt and hydrothermally-altered silicic rock. Thermomechanical modeling with a typical 0.001 km3/yr eruption rate of hydrous basalt into a 38 km Kamchatkan arc crust produces two magma bodies, one near the Moho and the other engulfing the entire section of upper crust. Rising basalts are trapped in the lower portion of an upper crustal magma body, which exists in a partially molten to solid state. Differentiation products of basalt periodically mix with the resident magma diluting its crustal isotopic signatures. At the end of the magmatism crust is thickened by 8 km. Thermomechanical modeling show that the most likely way to generate large spikes of rhyolitic magmatism is through delamination of cumulates and mantle lithosphere after many millions of years of crustal thickening. The paper also presents a chemical dataset for Pacific ashes from ODDP 882 and 883 and compares them to Karymshina ignimbrites and two other Pleistocene calderas studied by us in earlier works.