Report on Pavlof (United States) — November 1980
Scientific Event Alert Network Bulletin, vol. 5, no. 11 (November 1980)
Managing Editor: David Squires
Pavlof (United States) Lava fountaining and ash emission; possible lava flow
Please cite this report as:
Global Volcanism Program, 1980. Report on Pavlof (United States). In: Squires, D (ed.), Scientific Event Alert Network Bulletin, 5:11. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198011-312030.
55.417°N, 161.894°W; summit elev. 2493 m
All times are local (unless otherwise noted)
An eruption from Pavlof 11-12 November ejected large lava fountains and ash clouds that reached 11 km altitude, and may have produced lava flows.
A seismic station [8.5 km SE] of Pavlof registered a 2.5-minute burst of low-amplitude harmonic tremor beginning 5 November at 1351. Emission of steam, ash, and some blocks from a vent high on the NE flank started 8 November at 1047 and lasted about 5 minutes, without accompanying seismicity. A second burst of low-amplitude tremor occurred between 0536 and 0541 on 9 November.
In contrast to the pattern observed before eruptions in 1973, 1974, 1975, and 1976, virtually no additional seismic activity was recorded until a group of 7 low-frequency volcanic earthquakes occurred at about 2300 on 10 November. After an explosion event appeared on seismic records at 0243 on 11 November, 10 more low-frequency volcanic earthquakes were recorded between 0300 and 0400. Continuous harmonic tremor, of fairly low amplitude, began at 0608, but amplitude intensified around 0900.
Reeve Aleutian Airways pilot Everett Skinner saw rocks up to 1 m in diameter rising 10-30 m at 1315 on the 11th. An observer in Cold Bay, 60 km to the W, noted an increase in activity about 1600. Skinner returned to the vicinity between 1630 and 1700, reporting lava fountaining from the summit, a black cloud hugging the upper N flank, and an eruption column reaching an estimated 6 km altitude. Between 1800 and 2000, various witnesses reported lava fountaining to a maximum height of 300 m, and incandescent material moving down the N flank. A satellite image returned at 1958 shows a nearly circular plume, 15 km in diameter, N of the volcano. Activity was visible through the night from Cold Bay and the Sand Point area (50-65 km to the ENE).
The next morning, at 0946, a satellite image revealed a plume 160 km long and almost as wide spreading N of Pavlof. Spectral analysis and weather balloon data indicated that the plume reached 8-9 km above sea level. Pilot reports on 12 November placed the top of the eruption cloud at 9 km at 1000, 6 km at 1100, and 11 km at 1400. The eruption clouds were described as varying from ash-rich to ash-poor. A helicopter crew from KENI television, Anchorage, videotaped pulses and bursts of lava fountaining, rising 150-300 m between 1600 and 1700. The fountains emerged from a pre-existing vent high on the NE flank, the only vent confirmed active during the eruption.
Very high-amplitude harmonic tremor accompanied the eruption, reaching its strongest levels between 2000 on 11 November and 0700 on 12 November. Tremor ceased at 1835 on the 12th, when many B-type earthquakes began to be recorded.
By the morning of 13 November, the eruption had ended. Several hundred B-type events per day were recorded 14-15 November. Renewed high-amplitude tremor began 15 November at 1306, lasting until 1711. B-type earthquakes continued 16-19 November, but fewer than 100/day were recorded.
Geologic Background. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.
Information Contacts: S. McNutt and J. Davies, LDGO; A. Till, USGS, Anchorage; J. Kienle, Univ. of Alaska; G. Roberts, Cold Bay Weather Station; Cmdr. J. Hair, Marine Environmental Branch, Juneau.