Report on Bezymianny (Russia) — 23 July-29 July 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 July-29 July 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Bezymianny (Russia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 23 July-29 July 2003. Smithsonian Institution and US Geological Survey.
55.972°N, 160.595°E; summit elev. 2882 m
All times are local (unless otherwise noted)
A large explosion at Bezymianny on 26 July at 2220 produced an ash plume that rose to a height of ~8 km a.s.l. and drifted W. KVERT raised the Concern Color Code from Green to Red, the highest level. Prior to the eruption, a weak thermal anomaly was detected on satellite imagery on 6 July, and two shallow low-magnitude earthquakes were recorded on 23 and 25 July. On the 25th and 26th a several-pixel-large thermal anomaly and a gas-and-ash plume were seen on satellite imagery. On the 26th the active phase of the eruption lasted for ~4 hours. According to Yelizovo Airport Meteorological Center (AMC) and a pilot's report, by 26 July at 2226 the ash cloud was around 10-11 km a.s.l. On 27 July an ash cloud was visible 250-300 km W of the volcano and probable pyroclastic-flow deposits were seen on the volcano's SE flank. The same day the Concern Color Code was reduced from Red to Orange. No seismicity was recorded during 27-28 July and no visual information was available because Bezymianny was obscured by clouds. No new signs of eruptive activity were visible on satellite imagery after 26 July. On 29 July the Concern Color Code was further reduced from Orange to Yellow.
Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.