Report on Pavlof (United States) — June 1986

Scientific Event Alert Network Bulletin, vol. 11, no. 6 (June 1986)
Managing Editor: Lindsay McClelland

Pavlof (United States) Strombolian activity feeds lava flow; strong seismicity

Please cite this report as:

Global Volcanism Program, 1986. Report on Pavlof (United States). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 11:6. 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)

USGS personnel observed Strombolian activity from a new vent E of and ~100 m below the summit during fieldwork in the area 10 June-1 July. Activity was similar on each of seven occasions when the volcano was clearly visible. Spatter from the vent fell on the upper E flank, feeding a flow [see 11:4] that had reached ~1,100 m altitude by 15 June and had advanced to ~600 m altitude two weeks later. On 29 June, the flow was ~100 m wide at 750 m altitude. Some mudflow activity (2-3 lobes) was associated with the [spatter-fed] flow. Occasional moderate ash emission occurred but the largest ash columns rose only several hundred meters above the vent. On the NNE side of the summit, the vent that had been active for the past 15 years had enlarged, probably during the April eruption, but was only steaming in June. A flow fed by spatter from the old vent, probably in April, was snow-covered [see 11:7]. Thick April ashfalls were sampled NW of the volcano, and large April mudflows and significant flooding were evident.

When John Reeder flew past Pavlof on 8 July at 1500, ash ejection fed a plume that reached about 3900 m altitude and drifted approximately 15 km WSW. Flows were seen on the SE and N sides, and black ash covered the summit area.

Seismicity declined slightly 17 June, but was still strong as of 4 July. No harmonic tremor was recorded. Seismicity was stronger on GMT days 28 June and 1 July than other days between 17 June and 4 July, but USGS personnel did not observe significant fluctuations in eruptive activity.

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: T. Miller, USGS Anchorage; J. Taber, LDGO; J. Reeder, ADGGS.