Geologic Background
The modern Bezymianny volcano, much smaller in
size than its massive neighbors Kamen and Kliuchevskoi,
was formed about 5,000 to 5,500 years ago over a
late-Pleistocene lava dome complex and an older ancestral
volcano that was built about 11,000 to 7,000 years ago.
During the past 3,000 years, three periods of intensified
activity have occurred at Bezymianny. The latest period,
which was preceded by a 1,000 year quiescence, began with
the dramatic 1955-56 sector collapse forming a large
horseshoe-shaped crater.
Historic Activity:
- No eruptions of Bezymianny were known for more than
250 years after the Russian discovery of Kamchatka in
1697 (a total of 1000 years of quiescence).
- A new cycle of eruptive activity began with the
1955-56 catastrophic eruption and is continuing today.
Three stages are recognized: (1) A preclimactic stage
that consisted of intense seismic activity, vulcanian
explosive activity, and deformation of the summit area.
(2) A climactic stage including a directed blast that
destroyed the summit and plinian activity that erupted a
large volume of juvenile tephra and pyroclastic flows.
(3) A post-climactic stage characterized by growth of an
extrusive dome in the crater. Periodic dome growth has
occurred almost yearly since 1956.
- A large horseshoe-shaped crater was formed by
collapse of the summit and an associated lateral blast
during the 1955 eruption and the eruptive sequence was
basically the same as at Mt. St. Helens in 1980.
Recent Activity:
- A strong explosive eruption that began on the
afternoon of October 21, 1993 with little advance seismic
warning. Ashfall generally obscured the volcano, but ash
plumes were observed rising to 8-12 km altitude on
October 23-24 and reached 15 km altitude on the afternoon
of October 24. The eruption plume extended more than 100
km to the ESE. Another violent outburst occurred on
October 28, resulted in ashfall 45 km NNE of the volcano.
A steam-and-ash plume and extrusive dome growth were
still occuring on Nov. 12. Weak ash-falls in mid-Nov. but
by mid-Dec. the tremor level had fallen to about
background levels.
- On Jan. 3, 1994 a large steam-and-gas plume was seen
to extend 40 km NE and the next day 60 km NE. Several
gas-and-steam plumes were reported during July and
August. In early September a viscous lava flow was
reported from the extrusive dome. Small white steam cloud
observed in Nov. 1994.
- Reports on volcanoes in Kamchatka by the Kamchatkan
Volcanic Eruptions Response Team were suspended in Dec.
1994, due to lack of funding by the Russian government.
Occasional reports continued from other sources.
- An eruption occurred on Oct. 6, 1995, with ash cloud
reaching 10 km above sealevel. Ashfall was reported about
50 km NNE. Eruption had ended by next day.
- A viscous lava flow extruded from the top of dome
between Aug. 26 and Sept. 1, 1996. No ash explosions were
observed.
- Fumarolic plumes continued into 1997. On May 9 an
eruption plume rose to 4 km above the crater and extended
40 km SE. Ash clouds were reported until May 15. Steam
and gas plumes were reported during the last half of
July. An eruption on Dec. 5, produced a plume that
reached an elevation of 9 km.
- Several large explosions in February 1999. Fumarolic
plumes continued through end of year.
- Ash clouds and volcanic tremor in Feb. and March
2000. Continuing ash clouds in August and September.
Large ash explosions in late October.
- Explosive eruption on Aug 7, 2001 sent plume to about
10 km altitude.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 2, No. 3 to V. 13,
No. 4)
- Global Volcanism Network (V. 17, No. 5 to V. 25, No.
10).
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