|Holocene Kamchatka volcanoes||
Institute of Volcanology and Seismology
Global Volcanism Program number
55°58' N, 160°36' E, summit elevation 2,882 m
Bezymianny (Figs.1,2) is one of the most well-known Kamchatka volcanoes thanks to its catastrophic eruption in 1956, preceded by a failure of a 0.5 km3 portion of the volcanic edifice. Sequence of events was remarkably similar to the 1980 eruption of Mount St.Helens and included sector collapse, directed blast, and Plinian eruption (Gorshkov, 1959; Belousov and Bogoyavlenskaya, 1988).
Volcanic activity started in October 1955 from moderate explosive eruptions, which lasted for about half a year and deposited gray fine- to medium-grained ash. This activity followed a ~1000 years long dormancy (Braitseva et al., 1991). At the end of November, strong bulging of the southeastern slope of the volcano began (Gorshkov, 1959). On March 30 a climactic eruption occurred: failure of a 0.5 km3 portion of the volcanic edifice provoked catastrophic directed blast, which felled trees at a distance of 15 miles and was followed by strong Plinian activity. The detailed accounts of the eruption were presented by Gorshkov (1959) and Gorshkov and Bogoyavlenskaya (1965). G.S.Gorshkov (1963) identified this type of eruption as directed blast or Bezymianny-type eruption. As a result of 1956 sector collapse, a horseshoe-shaped crater open towards the east and a large debris avalanche deposit were formed (Figs.2-4). The deposits of the directed blast ("sand of the directed blast" or "blast surge deposits") cover an area of about 500 km2 (Gorshkov, 1959) and in many places are overlain with pyroclastic flow deposits (Fig.5).
Extrusive dome Novy ("New") started to grow inside the 1956 crater occasionally producing lava and pyroclastic flows (Figs.6, 7).
Bezymianny (“Nameless”) volcano is located on the southeast slope of the extinct Kamen volcano (Fig.1). The volcano had not erupted in historic time, and was over-shadowed by its gigantic neighbors, Kliuchevskoi and Kamen’. A row of domes exists at the southern and southwestern sides of the volcano (Fig.1). Some of the domes pre-date pre-Bezymianny volcano, which is believed to have originated 10-11 ka BP (Braitseva et al., 1991). Ashes from pre-Bezymianny are present in the soil-pyroclastic sequence around the volcano from Early Holocene till about 6900 14C years BP.
Bezymianny per se started to form about 4700 14C years BP after a long repose period (Braitseva et al., 1991). The volcanic edifice was built of pyroclastic material and lavas, erupted in spurts, most intensely between 4700-2750, 2100-1550 and 1200-1000 14C years BP. Identification of these active periods is based on the relationships of Bezymianny deposists with marker ash layers from Shiveluch (SH2, 950 yrs BP, Fig.4; SH3, 1400 yrs BP; SH5, 2550 yrs BP; SH2800, 2800 yrs BP), Ksudach (KS1, 1800 yrs BP) and Khangar (KHG, 6900 yrs BP) volcanoes (all ages are 14C). The largest of pre-historic explosive eruptions from Bezymianny occurred about 2100 yrs BP, after about 800 years of dormancy, and deposited coarse andesitic ash westwards of the volcano.
The volcano has been dormant for about 1000 years before the 1955 activity (Braitseva et al., 1991). Prior to 1955, the volcano had a summit elevation of about 3100 m a.s.l.
Bezymianny is composed mostly of medium-K calc-alkaline andesite with minor amounts of basaltic andesite and dacite. Amphibole, pyroxene and amphibole-pyroxene types of andesite have been identified (Bogoyavlenskaya et al., 1991).
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Alidibirov MA, Bogoyavlenskaya GE, Kirsanov IT, Firstov PP, Girina OA, Belousov AB, Zhdanova EYu, Malyshev AI (1990) Volcanology and Seismology 10: 839-863
Belousov AB and Bogoyavlenskaya GE (1988) Debris avalanche of the 1956 Bezymianny eruption. Proc.Kagoshima Int Conf on Volcanoes: 460-462
Belousov AB (1996) Pyroclastic deposits of March 30, 1956 directed blast at Bezymianny volcano. Bull Volcanol 57: 649-662
Belousov AB, Belousova MG (1998) Bezymiannyi eruption on March 30, 1956 (Kamchatka): sequence of events and debris-avalanche deposits. Volcanology and Seismology 20: 29-49
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Girina OA (1997) Pyroclastic surge deposits of Bezymianny volcano. Volcanology and Seismology 18/5: 547-560
Gorshkov GS (1959) Gigantic eruption of the volcano Bezymianny. Bull Volcanol 20: 77-109
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