Temporal irregularity of the output of volcanic material is studied for the sequence of large (V ≥ 0.5 km3, N = 29) explosive eruptions on Kamchatka during the last 10,000 years. Informally, volcanic productivity looks episodic, and dates of eruptions cluster. To investigate the probable self-similar clustering behavior of eruption times, we determine correlation dimension Dc. For intervals between events 800 and 10,000 years, Dc ≈ 1 (no self-similar clustering). However, for shorter delays, Dc = 0.71, and the significance level for the hypothesis Dc < 1 is 2.5%. For the temporal structure of the output of volcanic products (i.e., for the sequence of variable-weight points), a self-similar “episodic” behavior holds over the entire range of delays 100–10,000 years, with Dc = 0.67 (Dc < 1 at 3.4% significance). This behavior is produced partly by the mentioned common clustering of event dates, and partly by another specific property of the event sequence, that we call “order clustering”. This kind of clustering is a property of a time-ordered list of eruptions, and is manifested as the tendency of the largest eruptions (as opposed to smaller ones) to be close neighbors in this list. Another statistical technique, of “rescaled range” (R/S), confirms these results. Similar but weaker-expressed behavior was also found for two other data sets: historical Kamchatka eruptions and acid layers in Greenland ice column. The episodic multiscaled mode of the output of volcanic material may be a characteristic property of a sequence of eruptions in an island arc, with important consequences for climate forcing by volcanic aerosol, and volcanic hazard.

A new Klyuchevskoy volcano eruptive cycle encompasses terminal (March 30, 1972 to August 23, 1974) and lateral (August 23, 1974 to December, 1974) eruption stages. The terminal eruption stage resulted in lava flows and parasitic cones that formed on the south-western flank of the volcano.
Eruption products are moderately alkalic high-alumina olivine-bearing andesite-basalts. The terminal eruption stage was accompanied by volcanic earthquakes and volcanic tremor. The lateral eruption was accompanied by explosive earthquakes. Volcanic tremor was the most useful prognostic sign indicating the onset of the lateral eruption. Eruptive mechanisms are discussed.

We determine a 3-D P-wave velocity structure of the mantle down to 700 km depth under the Kamchatka peninsula using 678 P-wave arrival times collected from digital seismograms of 75 teleseismic events recorded by 15 portable seismic stations and 1 permanent station in Kamchatka. The subducting Pacific slab is imaged clearly that is visible in the upper mantle and extends below the 660-km discontinuity under southern Kamchatka, while it shortens toward the north and terminates near the Aleutian–Kamchatka junction. Low-velocity anomalies are visible beneath northern Kamchatka and under the junction, which are interpreted as asthenospheric flow. A gap model without remnant slab fragment is proposed to interpret the main feature of high-V anomalies. Combining our tomographic results with other geological and geophysical evidences, we consider that the slab loss may be induced by the friction with surrounding asthenosphere as the Pacific plate rotated clockwise at about 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow and the presence of Meiji seamounts. As a result, the slab loss and the subducted Meiji seamounts have jointly caused the Pacific plate to subduct under Kamchatka with a lower dip angle near the junction, which made the Sheveluch and Klyuchevskoy volcanoes shift westward.

Pb isotope data are used to constrain the chemical contribution of the subducted components in the recycling beneath Klyuchevskoy volcano, the most active volcano in the Kamchatkan arc. The Pb isotope ratios of Klyuchevskoy basalts (206Pb/204Pb= 18.26–18.30, 207/Pb204Pb= 15.45–15.48, 208/Pb204Pb= 37.83–37.91) define a narrow range that falls within the Pacific mid-ocean ridge basalt (MORB) field and are among the least radiogenic island arc basalts measured to date. These data are similar to data from three other Quaternary Kamchatkan volcanoes: Tolbachik, Kumroch-Shish, and Maly Semiachik. In contrast, North Pacific sediments (primarily siliceous oozes) collected parallel to the Kamchatkan trench during Ocean Drilling Program Leg 145, have Pb isotope ratios (206Pb/204Pb= 18.51–18.78, 207Pb/204Pb= 15.56–15.64, 208Pb/204Pb= 38.49–38.75) that are more radiogenic than either the Klyuchevskoy basalts or Pacific MORB. Incorporation of even a small amount of sediment in the source of the Klyuchevskoy magmas would shift the Pb isotope ratios of the erupted basalts from the MORB field to more radiogenic values. The absence of 10Be and elevated Pb isotope ratios in the Kamchatkan volcanic lavas, despite the presence of distinctively radiogenic Pb in the North Pacific sediments makes it unlikely that sediments or sediment-derived fluids are involved in the source magmas beneath Kamchatka. The Kamchatkan arc thus represents an “end-member” whereby little or no sediment is involved in terms of elemental recycling and arc magma genesis. The major and trace elements, Pb, Sr and Nd isotope data of the Kamchatkan basalts are most consistently explained if derived from a fluid-fluxed, peridotitic mantle wedge source, wherein the fluid composition is dominantly controlled by dehydration of altered oceanic crust, imparting a radiogenic 87Sr/86Sr, and MORB-like Pb isotope signature to the mantle source. The erupted Klyuchevskoy lavas preserve a slab signature derived from incompatible elements that are strongly partitioned into the fluid. The 30 km of arc crust through which the Klyuchevskoy magmas traverse prior to eruption is not composed of older crust, but must be juvenile, similar in isotopic composition to MORB.

AAbstract—Numerous summit and parasitic eruptions of moderate potassium magnesian and high-alumina basalts and basaltic andesites, their mineralogic and geochemical features, and the composition of in situ chilled melt inclusions in the olivine of cinder lapilli discharged by Klyuchevskoi Volcano all provide evidence of the presence of magma chambers beneath the volcano. This is also supported by a dualism in the variation of CaO and A1203 concentrations in olivine and clinopyroxene during crystallization. The mineralogic features in the high-alumina basalts that were discharged by all parasitic eruptions of Klyuchevskoi provide evidence of magnesian magma being emplaced from a deeper chamber into a shallow high-alumina chamber. The distribution of incoherent elements in the volcano's magnesian and aluminiferous rocks shows that they came from a single mantle source. The geochemical and mineralogic data are in good agreement with the results of geophysical surveys that concern the structure and properties of the lithosphere beneath Klyuchevskoi.