Detailed studies of volcanic tremor envelopes with frequencies ranging from 5.5⋅10-6 to 2.5⋅10-2 Hz (50 hrs - 40 sec), recorded during the Klyuchevskoi volcano eruptions of 1983 and 1984, revealed five major frequencies: 1.1⋅10-2 Hz (T1 = 1 min 34 sec), 2.5⋅10-3 Hz (T2 = 6 min 10 sec), 4.2⋅10-4 Hz (T3 = 40 min), 5.1⋅10-5 Hz (T4 = 5 hrs 30 min), 7.7⋅10-6 Hz (T5 = 36 hrs), as well as superpositions of their harmonics. In the 1993 eruption, fluctuations in the volcanic tremor envelopes have frequencies of TI = 2 hrs 48 min and TII = 6 hrs 12 min, which correspond to periodicities in the dynamics of eruptions identified by visual observations since 1932. The distribution of peak amplitudes has been found to vary in relation to eruption intensity—increasing eruption strength correlates with an increase in the amplitude of low frequency peaks, and vice versa. It is concluded that volcanic tremor allows monitoring of eruption dynamics. Possible reasons for the occurrence of periodicities are discussed, but a comprehensive model for this phenomenon has not yet been developed.

The Holocene eruptive history of Shiveluch volcano, Kamchatka Peninsula, has been reconstructed using geologic mapping, tephrochronology, radiocarbon dating, XRF and microprobe analyses. Eruptions of Shiveluch during the Holocene have occurred with irregular repose times alternating between periods of explosive activity and dome growth. The most intense volcanism, with frequent large and moderate eruptions occurred around 6500–6400 BC, 2250–2000 BC, and 50–650 AD, coincides with the all-Kamchatka peaks of volcanic activity. The current active period started around 900 BC; since then the large and moderate eruptions has been following each other in 50–400 yrs-long intervals. This persistent strong activity can be matched only by the early Holocene one.
Most Shiveluch eruptions during the Holocene produced medium-K, hornblendebearing andesitic material characterized by high MgO (2.3–6.8 wt %), Cr (47–520 ppm), Ni (18–106 ppm) and Sr (471–615 ppm), and low Y (> 18 ppm). Only two mafic tephras erupted about 6500 and 2000 BC, each within the period of most intense activity.
Many past eruptions from Shiveluch were larger and far more hazardous then the historical ones. The largest Holocene eruption occurred ∼1050 AD and yielded >2.5 km3 of tephra. More than 10 debris avalanches took place only in the second half of the Holocene. Extent of Shiveluch tephra falls exceeded 350 km; travel distance of pyroclastic density currents was > 22 km, and that of the debris avalanches ≤20 km.

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.

New and published data on the composition of melt inclusions in olivine (Fo73_yi) from volcanoes of the Kamchatka and northern Kurile Arc are used 1) to evaluate the combined systematics of volatiles (H2O, S, Cl, F) and incompatible trace elements in their parental magmas and mantle sources, 2) to constrain thermal conditions of mantle melting, and 3) to estimate the composition of slab-derived components. We demonstrate that typical Kamchatkan arc-type magmas originate through 5-14% melting of sources similar or slightly more depleted in HFSE (with up to -1 wt.% previous melt extraction) compared to MORB-source mantle, but strongly enriched in H2O,B, Be, Li, Cl. F, LILE, LREE, Th and U. Mean H2O in parental melts f 1.8-2.6 wt.%) decreases with increasing depth to the subducting slab and correlates negatively with both 'fluid-immobile* (e.g. Ti, Na, LREE) and most 'fluid-mobile' (e.g. LILE, S, Cl, F) incompatible elements, implying that solubility in hydrous fluids or amount of water does not directly control the abundance of 'fluid-mobile' incompatible elements. Strong correlation is observed between H2O/Ce and B/Zr (or B/LREE) ratios. Both, calculated H2O in mantle sources (0.1-0.4%) and degrees of melting (5-14%) decrease with increasing depth to the slab indicating that the ultimate source of water in the sub-arc mantle is the subducting oceanic plate and that water flux (together with mantle temperature) governs theextent of mantle melting beneath Kamchatka. A parameterized hydrous melting model [Katzetal. 2003, G3,4(9), 1073] is utilized to estimate that mantle melting beneath Kamchatka occurs at or below the dry peridotite solidus (1245-1330 °C at 1.5-2.0 GPa). Relatively high mantle temperatures (yet lower than beneath back-arc basins and ocean ridges) suggest substantial corner flow driven mantle upwelling beneath Kamchatka in agreement with numerical models implying non-isoviscous mantle wedge rheology. Data from Kamchatka, Mexico and Central America indicate that <5% melting would lake place beneath continental arcs without water flux from the subducting slab. A broad negative correlation appears to exist between crustal thickness and the temperature of magma generation beneath volcanic arcs with larger amounts of decompression melting occurring beneath thinner arc crust (Uihosphere). In agreement with the high mantle temperatures, we observe a systematic change in the composition of slab components with increasing slab depth from solute-poor hydrous fluid beneath the volcanic front to solute-rich hydrous melt or supercritical liquid at deeper depths beneath the rear arc. The solute-rich slab component dominates the budget of LILE, LREE,Th and U in the magmas and originates through wet-melting of subducted sediments and/or altered oceanic crust at > 120 km depth. Melting of the upper parts of subducting plates under water flux from deeper luhosphere (e.g. serpentinites), combined with high .emperatures in the mantie wedge, may be a more common process beneath volcanic arcs than has been previously recognized. 0 2006 Klsevier B.V. All rights reserved.

Lavas from Klyuchevskoy and Bezymianny volcanoes, Kamchatka, appear to show a link between the extent of partial melting in their mantle source region and the subsequent degree of fractionation suffered by the magmas during passage through the crust. This fractionation may have occurred on timescales significantly less than 1000 years if observed 226Ra excesses largely reflect variable residual porosity in the source melting region. Unlike most arc lavas, those with the highest MgO contents and Ba/Th ratios have the lowest 226Ra excess. Forward models suggest that those portions of the source which had undergone the greatest addition of U by fluids from the subducting plate also underwent the greatest extents of partial melting at the highest residual porosity. At Kluchevskoy, a change from eruption of high-MgO to high-Al2O3 basaltic andesites around 1945 is reflected in an increase in size of 226Ra excess which seems to require a simultaneous decrease in residual porosity and suggests a rapid changes in the melting regime. The eruption of andesites at Bezyminanny, simultaneous with the eruption of basaltic andesites at Klyuchevskoy, further suggests that different degree melts produced at differing residual porosity can be formed and extracted from the melt region at the same time. Thus, the melting processes beneath Klyuchevskoy and Bezyminanny are demonstrably complex. They have clearly been influenced by both fluid addition from the subducting plate and extension and decompression beneath the Central Kamchatka Depression. Finally, the 210Pb data are, with one or two exceptions, in equilibrium with 226Ra, suggesting that there was restricted relative magma-gas movement in this highly productive magmatic system.

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.

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.