Report on Pavlof (United States) — August 1996

Bulletin of the Global Volcanism Network, vol. 21, no. 8 (August 1996)
Managing Editor: Richard Wunderman

Pavlof (United States) Vigorous seismicity and intermittent eruptive activity

Please cite this report as:

Global Volcanism Program, 1996. Report on Pavlof (United States). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 21:8. Smithsonian Institution.

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United States

55.417°N, 161.894°W; summit elev. 2493 m

All times are local (unless otherwise noted)

Residents of the Alaska Peninsula first noticed small glowing plumes from Pavlof on 15 September. During the following week, seismicity was vigorous and eruptions were intermittent. Poor weather in the first week inhibited visual observations.

On the morning of 16 September, AVO received a report from residents of Cold Bay about an unusual plume emanating from the N flank of the volcano. Local pilots reported glow near the summit and large "car-sized" fragments being ejected from the summit vent. Satellite imagery showed a hot spot in the vicinity of the cone. Seismic data from stations on and near the volcano suggested a low-level eruption. By that afternoon eruptive activity had declined somewhat, although seismicity indicative of eruption remained sporadic.

Persistent seismic activity suggested that an episodic, low-level eruption continued during 17-22 September. The summit hot spot was not seen on images obtained on the early morning of 17 September. Several periods of increased seismicity from the afternoon of 17 September to the morning of 18 September suggested that the eruption was episodic in character with ejection of ash and bombs up to 300 m above the summit of the cone.

Intermittent low-level ash clouds were detected on satellite imagery on 18 September, although imagery from that afternoon to the next morning showed no ash cloud. Pilot reports on 18 September confirmed that there was no significant ash venting above the cloud tops at 3,000 m altitude. Satellite imagery from the afternoon of 19 September to the morning of 20 September also detected no ash cloud.

From the afternoon of 20 September to the afternoon of 22 September several periods of increased seismicity were observed and intermittent low-level ash clouds were detected on satellite imagery. On 23 September local observers confirmed Strombolian fountaining 150-200 m above the summit. There were no major explosions.

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: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.