Report on Pavlof (United States) — 23 March-29 March 2016

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 March-29 March 2016
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2016. Report on Pavlof (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 23 March-29 March 2016. Smithsonian Institution and US Geological Survey.

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Pavlof

United States

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

All times are local (unless otherwise noted)


AVO reported that seismicity at Pavlof began to increase at about 1553 on 27 March, characterized by a quick onset of continuous tremor. An ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. and by 1618 was drifting N. AVO raised the Aviation Color Code to Red and the Volcano Alert Level to Warning. During the night lava fountaining from the summit crater was observed by mariners, pilots, and residents of Cold Bay (60 km SW). Lahars likely descended the flanks. Tremor levels remained high on 28 March. Lightning in the ash plume was detected in the morning, and infrasound data from a sensor network located in Dillingham (650 km away) also indicated sustained ash emissions. At 0700 a continuous ash plume was evident in satellite images drifting more than 650 km NE. A SIGMET issued by the National Weather Service (NWS) Alaska Aviation Weather Unit indicated that the maximum ash-cloud altitude was 11 km (37,000 ft) a.s.l. Strongly elevated surface temperatures suggested the presence of surficial lava flows.

The intensity of the eruption significantly declined at 1230 on 28 March; seismicity and infrasound signals decreased to low levels. AVO lowered the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Seismic tremor was slightly above background levels. Ash emissions decreased through the night and were barely visible in a satellite image acquired at 0625 on 29 March. Remnant ash continued to drift over Bristol Bay and areas of interior Alaska. The webcam recorded intermittent, low-level ash plumes rising as high as 4.6 km (15,000 ft) a.s.l.

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.

Source: US Geological Survey Alaska Volcano Observatory (AVO)