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U.S. Geological Survey
Monday, August 8, 2016, 11:44 AM AKDT (Monday, August 8, 2016, 19:44 UTC)

55°25'2" N 161°53'37" W, Summit Elevation 8261 ft (2518 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Synopsis of Recent Volcanic Unrest and Status of Monitoring Capabilities at Pavlof Volcano, June-August 2016

Intermittent low-level volcanic unrest has been occurring at Pavlof Volcano from late June through early August 2016. The unrest has been characterized by minor emissions of dark-colored ash and steam that reach as high as about 15,000 ft (4.5 km) above sea level (asl) and are occasionally visible in satellite and web camera views of the volcano and by pilots and observers in local communities. Fallout of ash has been limited to the flanks of the volcano and the immediate area surrounding Pavlof. Amounts of ash fall have been low—probably only a fraction of an inch.

Chronology of Recent Events
Pavlof erupted suddenly and vigorously on March 27, 2016, for about 20 hours, sending ash as high as 37,000 ft asl and producing an ash cloud that extended at least 400 miles (640 km) northeast of the volcano. Following this event, the volcano was quiet until a short lived and more modest period of ash emission occurred in mid-May. More recently, an increase in seismicity, weak thermal signals at the summit, and web camera observations of steaming, prompted AVO to raise the Aviation Color Code and Volcano Alert Level to Yellow/Advisory on 1 July. The volcano remained relatively quiet until July 11 when discrete ash bursts were observed in web camera images beginning around 13:00 AKDT (21:00 UTC). These ash emissions reached at most a few hundred feet above the summit vent and extended a few miles beyond the volcano. Ash and steam emissions slowly declined and by about 21:20 AKDT 12 July (05:20 UTC 13 July), ash emissions were no longer visible in web camera or satellite data. On 27 July, vigorous, steam and ash emissions were observed in web camera images, satellite images and by a passing pilot. The diffuse ash-steam plume reached about 15,000 ft (4.5 km) asl extending for as much as 100 miles (60 km) northwest of the volcano. Seismic tremor did not change appreciably during this period, but the more energetic nature of the ash and steam emissions prompted AVO to raise the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. Since the ash and steam burst on 27 July, unrest at the volcano has declined and on 4 August, AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. The volcano remains in a restless condition and low-level seismic tremor is continuing.

Current monitoring capabilities
To help address the challenges of monitoring Pavlof, AVO scientists visited the volcano in early July and made repairs and digital upgrades to the seismic monitoring network, including the replacement of a seismic station on the north flank that was destroyed during the 27–28 March 2016 eruption, installation of two infrasound sensors to detect explosions, and a new web camera located in the Black Hills area north of the volcano near the Bering Sea coast (http://www.avo.alaska.edu/webcam/Pavlof_-_BLHA.php). As a result of this work, the geophysical monitoring network at Pavlof has been restored and improved to greater functionality than before. Digital instrumentation and telemetry upgrades of two sites on the north flank of the volcano have increased AVO’s ability to detect unrest. Many of the geophysical data streams collected at Pavlof are now monitored continuously using computer-aided alarm systems which also improves AVO’s ability to respond to changes in unrest at Pavlof.

Analysis and Prognosis
Pavlof Volcano is one of the most frequently active volcanoes in the Aleutian arc, and the current unrest reflects behavior that is typical for Pavlof. Low-level ash and steam emissions could continue for several weeks or months, based on the pattern of its past eruptions. AVO is unable to predict the how long the current activity will last with any degree of certainty, but our current instrumentation network provides improved capabilities to monitor and interpret the volcanoes behavior.

Pavlof’s eruptive style is consistent with an “open-system” volcano, where a conduit from magma source to surface allows vigorous degassing and does not require breaking of rock for magma to reach the surface. The level of unrest can change rapidly and the volcano is capable of erupting explosively with little precursory seismicity and correspondingly short alert times.

Ash clouds generated by typical Pavlof eruptions usually do not reach much above 20,000 ft above sea level; however, occasional energetic explosive events can produce more robust ash clouds that have reached as high as 35,000–50,000 ft. (9–15 km) and extended 200–400 miles (322–644 km) beyond the volcano on several occasions in the past 30 years. During these larger ash-producing eruptive events, it is possible for communities in the region, including Cold Bay, Nelson Lagoon, Sand Point, and King Cove to receive trace (<1/32 inch) to minor (1/32– 1/4 inches) amounts of ash fall.


Other Alaska volcanoes show no signs of significant unrest: http://www.avo.alaska.edu/activity/

AVO scientists conduct daily checks of earthquake activity at all seismically-monitored volcanoes, examine web camera and satellite images for evidence of airborne ash and elevated surface temperatures, and consult other monitoring data as needed.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php


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John Paskievitch, Acting Scientist-in-Charge, USGS
jpaskie@usgs.gov (907) 786-7497

Jeff Freymueller, Coordinating Scientist, UAFGI
jfreymueller@alaska.edu (907) 322-4085

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.
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