Vol 13, No 3 (2019)

This paper presents new data on the age and isotope geochemistry for plateau effusive rocks sampled from the Central Kamchatka Depression and Nikolka Volcano. We have compared these materials with data on rocks sampled in the Klyuchevskaya Group of Volcanoes, as well as from Shiveluch, Kharchinsky, Zarechnyi, Nachikinsky, and Bakening volcanoes, and from an “NEB-adakite” Pliocene shield volcano in the interfluve between the Ozernaya Kamchatka and the Pravaya Kamchatka rivers. We show that the relatively “advanced,” in the sense of evolution, (mostly alkaline) compositions of rocks sampled from Nachikinsky, Bakening, and Nikolka volcanoes, as well as from the Pliocene shield edifice, have isotope characteristics that are significantly different from those for the Klyuchevskaya Group of Volcanoes. This type of rock is typical of the CKD as a rifting structure. The rocks in the Klyuchevskaya Group of Volcanoes are not typomorphic for this structure and reflect the phase of ordinary orogenic volcanism that has involved a much larger area. The Miocene plateau effusive rocks are only different from the rocks of this group in having a slightly higher potassium alkalinity. Rocks of the rifting type can be recognized, not only by their higher alkalinity, but also by a definite relationship among microcomponents: Ti/V > 0.004, Nb/Y > 0.28, Dy/Yb > 2.00, La/Yb > 6.5, Sm/Yb > 2.4, Lu/Hf < 0.08. Along with the isotope characteristics, these relationships suggest the existence of a common deep-seated asthenospheric mantle reservoir for the parent melts. The area of junction between the Kuril–Kamchatka and the Commander-Islands–Aleutian island arc system is marked by a higher fluid enrichment (the cerium REE group) in melts for rocks of some volcanoes, viz., Shiveluch, Kharchinskii, and Zarechnyi.

Large explosive eruptions of volcanoes pose the highest hazard to modern jet flights, because such eruptions can eject as much as several cubic kilometers of volcanic ash and aerosol into the atmosphere during a few hours or days. The year 2016 saw eruptions on 5 of the 30 active Kamchatka volcanoes (Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Zhupanovsky) and on 3 of the 6 active volcanoes that exist on the North Kuril Islands (Alaid, Ebeko, and Chikurachki). Effusive activity was observed on Sheveluch, Klyuchevskoy, Bezymianny, and Alaid. All volcanoes showed explosive activity. The large explosive events mostly occurred from September through December (Sheveluch), a moderate ash emission accompanied the entire Klyuchevskoy eruption in March–November, and explosive activity of Karymsky, Zhupanovsky, Alaid, and Chikurachki was mostly observed in the earlier half of the year. The ash ejected in 2016 covered a total area of 600 000 km², with 460 000 km² of this being due to Kamchatka volcanoes and 140 000 km² to the eruptions of the North Kuril volcanoes. The activity of Sheveluch, Klyuchevskoy, and Zhupanovsky was dangerous to international and local flights, because the explosions sent ash to heights of 10–12 km above sea level, while the eruptions of Bezymianny, Karymsky, Alaid, Ebeko, and Chikurachki were dangerous for local flights, since the ash did not rise higher than 5 km above sea level.

Quantitative estimates of present-day lateral ground surface displacement rates in southern Yakutia were obtained during recent years by setting up the first (and the only so far) stations of continuous GPS observation at the town of Neryungri (NRG) and at the town of Chul’man (CHL3). Both stations are in the southern margin of the Eurasian plate, near the system of active structures that separate it from the Amur plate. For an estimate of relative displacement we chose a period of joint operation at these two GPS stations, viz., from June 29, 2015 to December 1, 2016. The rate of displacement at Neryungri as calculated for a 5-year term (between October 27, 2011 and October 1, 2016) was 21.83 ± 0.73 mm/yr in the east–west direction and 12.26 ± 0.25 mm/yr in the north–south direction based on the ITRF2014 frame. The resulting values are little different from the theoretical rates of motion for the Eurasian plate at this point. The difference between measured rates and those for the well-known kinematic model for the Eurasian plate as developed in this study is |0.5| mm/yr for the east component and |1.0| mm/yr for the north component; these values are in agreement with results of other authors (Kreemer et al., 2014; Ashurkov et al., 2016). The accuracy of determination for the rates of lateral ground motion at CHL3 should enhanced by making measurements synchronously with the NRG2 station.