Bezymyannyi: "Anatomy" of Volcano

By the time I began my observations, Bezymyannyi was a volcanic cone of a complex type. The caldera that had been produced by a lateral blast in 1956 contained a dome, named Novyi, that had grown in the explosion vent during the eruptions that followed the blast. The dome consisted of two blocks: one of them, passive, in the west, consisted of the old extrusive rocks of the earliest eruptions and exhibited merely fumarolic activity throughout the period of study, the other, active, in the east, composed of a stratovolcanic complex produced by the eruptions of the previous years.

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Bezymyannyi structure in 1979:
I - remains of old volcano, destroyed by directed eruption in 1956.
II - extrusive dome growing up in volcano's crater after 1956.
III - active volcano's block. All eruptions from middle of the seventies were associated with this block.
1 - extrusion rocks; 2 - old volcano's rocks; 3 - zone of fragmentation in old volcanic structure; 4 - magmatic channel; 5 - lava flows; 6 - mantle of extrusive dome; 7 - clastic deposits of last eruptions.

During the 1980s Volcano was in the intermediate state between the moderately acid extrusive and the basic stratovolcanic activity as follows from its rapid evolution in terms of the eruptive forms, the composition of the juvenile material, and structural adjustment. This transition defined the peculiar dynamics of its eruptions.

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