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 SiO 2 >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 87 Sr/ 86 Sr ratios from 0.70334 to 0.70366, but have almost constant Nd isotopic ratios ( 143 Nd/ 144 Nd 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 14 C dating that permits analysis of time-space patterns of volcanic activity, evolution of the erupted products, and volcanic hazards.

Abstract. Tephra layers produced by volcanic eruptions are widely used for correlation and dating of various deposits and landforms, for synchronization of disparate paleoenvironmental archives, and for reconstruction of magma origin. Here we present our original database TephraKam, which includes chemical compositions of volcanic glass in tephra and welded tuffs from the Kamchatka volcanic arc. The database contains 7049 single-shard major element analyses obtained by electron microprobe and 738 trace element analyses obtained by laser ablation inductively coupled plasma mass spectrometry on 487 samples collected in close proximity to their volcanic sources in all volcanic zones in Kamchatka. The samples characterize about 300 explosive eruptions, which occurred in Kamchatka from the Miocene up to recent times. Precise or estimated ages for all samples are based on published 39Ar∕40Ar dates of rocks and 14C dates of host sediments, statistical age modeling and geologic relationships with dated units. All data in TephraKam are supported by information about source volcanoes and analytical details. Using the data, we present an overview of geochemical variations in Kamchatka volcanic glasses and discuss applications of these data for precise identification of tephra layers, their source volcanoes, and temporal and spatial geochemical variations in pyroclastic rocks in Kamchatka. The data files described in this paper are available on ResearchGate at https://doi.org/10.13140/RG.2.2.23627.13606 (Portnyagin et al., 2019).

23The ~16 ka long record of explosive eruptions from Shiveluch volcano (Kamchatka, NW 24 Pacific) is refined using geochemical fingerprinting of tephra and radiocarbon ages. Volcanic 25 glass from 77 prominent Holocene tephras and four Late Glacial tephra packages was analyzed 26 by electron microprobe. Eruption ages were estimated using 113 radiocarbon dates for proximal 27 tephra sequence. These radiocarbon dates were combined with 76 dates for regional Kamchatka 28 marker tephra layers into a single Bayesian framework taking into account the stratigraphic 29 ordering within and between the sites. As a result, we report ~1700 high-quality glass analyses 30 from Late Glacial-Holocene Shiveluch eruptions of known ages. These define the magmatic 31 evolution of the volcano and provide a reference for correlations with distal fall deposits. 32

Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km 2 of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach F3 km 3 . The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530-4350 BC. From F2490 BC at least 13 avalanches occurred after intervals of 30-900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30-340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events.

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