Fig.1

Fig.2

Fig.3

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Fig.5

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Fig.7

Fig.8

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Fig.10

Krasheninnikov volcano looks rather dull from afar (Fig.1): it is composed of two large coalesced cones and is nested in a <39 ka-old caldera (Florensky, 1989; Braitseva et al., 1995). However, an aerial view of the volcano exhibits its "inner beauty" (Figs. 2 and 3). The northern cone resembles a matryoshka doll: it is crowned with a caldera, the caldera encloses a small stratovolcano, and the crater of this volcano hosts a small lava cone. Multiple adventive vents are located on the flanks of the volcano and outside the <39 ka-old caldera (map). The latter are aligned along the fissure zones parallel to the general strike of the Eastern volcanic belt (Fig. 4). Eruptive products of the volcano itself range from basalt to dacite, while lavas of the vents outside the Late Pleistocene caldera are dominantly basalts-basaltic andesites. Petrological and geochemical studies (Volynets et al., 1989) suggest that all these rock varieties belong  to the same medium-K₂O two-pyroxene-plagioclase series and have originated as a result of fractionation of an initial mafic melt. Thus, all the considered vents likely belong to the same magmatic system. Landslide and rockfall deposits derived from the volcano slopes overlap some lava flows. No historical eruptions of Krasheninnikov volcano are known, but it was termed active based on fresh morphology (Vlodavets, 1957) and weak fumarolic activity (Shteinberg, 1964).

40 sections of the Holocene soil-pyroclastic cover blanketing glacial deposits and more than 60 shorter sections of the cover overlying individual lava flows and landslide deposits were measured around the volcano (Ponomareva, 1990). This has allowed compilation of the summary stratigraphy of fall deposits that records the explosive activity of the volcano during the Holocene (summary section). Periods of volcanic rest are recorded by sandy loams or soils. Lava flow and rockslide deposits have been fitted into the overall stratigraphic succession by study of the soil-pyroclastic cover overlying each of the units. Radiocarbon ages of the individual units were determined with the help of dated regional and local marker ash layers and additional radiocarbon dates (Ponomareva, 1990; Braitseva et al., 1997 b). Radiocarbon ages were converted to calendar years using the procedure of Stuiver and Reimer (1993) in order to calculate the duration of repose periods.

Summary stratigraphy of all the erupted products including both tephra and lava allows to reconstruct its eruptive history (summary section). Eruptions separated from each other by intervals less than 100 years are combined into active periods. We can identify repose periods separating active periods or single eruptions and estimate their duration. Krasheninnikov volcano was repeatedly active during the Holocene time. At first South Cone was built. Its formation was initially accompanied by eruptions of the Southern cinder cones outside the caldera and later by those of the Northern cones. Last eruptions of South Cone were followed by a 900-year-long quiescence inside the caldera, after which the conduit shifted 2 km north and the North Cone started to form on the slope of the older one. If we consider the whole magmatic system including both intra- and extra-caldera vents, we may see that while the volcano itself was silent, several eruptions of the Northern cones occurred (Figs. 2 and 5). That means that the magma came up to the surface but found it easier to make its way through newly formed dykes than use the old conduit. In this sense the repose period of the whole volcanic center was much shorter.

The last eruptions of Krasheninnikov volcano (inner lava cone and lava flows X) occurred only about 400-600 years ago, after a repose period of few hundred years (Ponomareva, 1990). Thus, our studies confirmed that Krasheninnikov volcano was recently active (Vlodavets, 1957).

Literature

Braitseva OA, Florenskii IV, Ponomareva VV, Litasova SN (1989) The history of the activity of Kikhpinych volcano in the Holocene. Volcanol Seismol  7:  845‑872

Braitseva OA, Melekestsev IV, Ponomareva VV, Sulerzhitsky LD (1995) The ages of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region, Russia. Bull Volcanol 57 (6): 383-402

Braitseva OA, Ponomareva VV, Sulerzhitsky LD, Melekestsev IV, Bailey J (1997b)  Holocene key-marker tephra layers in Kamchatka, Russia. Quaternary Res 47 (2): 125-139

Fedotov SA, Masurenkov YuP (eds) (1991) Active volcanoes of Kamchatka. Nauka, Moscow. Vol.1, 302 p. Vol.2, 415 p.

Ponomareva VV, Tsyurupa AA (1985) On the long silicic lava flows at the Krasheninnikov volcano. Volcanol Seismol 3:. 85-92

Ponomareva VV (1990) The history of Krasheninnikov volcano and the dynamics of its activity.  Volcanol Seismol  9: 714-741

Ponomareva VV, Braitseva OA (1991) Volcanic Hazards Assessment in the Area of lake Kronotskoye, Uzon caldera and Valley of Geysers. Volcanol Seismol12: 42-69

Shteinberg GS (1964) On activity and structure of Krasheninnikov volcano. Bull Volcanol Stancii 37: 16-20  (in Russian)

Volynets ON, Ponomareva VV, Tsyurupa AA (1989) Petrological and tephrochronological studies of Krasheninnikov volcano, Kamchatka. Int Geol Rev 31(1): 1107-1122