Volcano Update from Archive

Thursday, June 13, 2013 3:15 PM AKDT (Thursday, June 13, 2013 23:15 UTC)

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

Pavlof Volcano is one of the most frequently active volcanoes in Alaska with over 40 historical eruptions. The current eruption is characterized by small explosions, lava fountaining, intermittent ash plumes that reach altitudes of 15,000 to 22,000 ft above sea level, and small flows of lava and mud on the volcanoes flanks, and is similar to previous historical eruptions. AVO is monitoring the eruption using a combination of seismic, satellite, and infrasound data as well as information obtained from local observations, web cameras, and pilot reports.

Chronology of Events
May 13-24, 2013: Seismic activity and elevated temperatures at the summit observed in satellite images indicated that an eruption of Pavlof Volcano was underway on the morning of May 13. This prompted AVO to raise the Volcano Alert Level and Aviation Color Code to Watch/Orange on May 13. Later that day, pilot reports and web camera views of steam and ash confirmed the eruption. During the first two weeks of the eruption, the activity was characterized by low-level, diffuse ash emission to heights of 15,000-22,000 ft. above sea level, and lava flows fed by lava-fountaining that descended from near the summit down the northwest flank. The most extensive ash plume observed reached about 22,000 ft. above sea level and a maximum length of about 250 miles (400 km) on May 18.

Through this period the seismicity was characterized by nearly continuous volcanic tremor with occasional discrete explosions that were detected by infrasound arrays on Akutan and Umnak Islands and in Dillingham.

Trace amounts of ash fall resulting in a thin film of ash on windshields was reported at Sand Point on May 18 and Nelson Lagoon on May 19-20. AVO received a sample of ash collected by a resident of Sand Point and that is primarily composed of volcanic glass shards.
An ASTER satellite image obtained on May 19 showed that lahars (volcanic mudflows) had formed on the north flank of the volcano and entered the upper Cathedral River drainage. No evidence for extensive inundation by lahars was observed in the Leontovich or Caribou River drainages on the north side of the volcano, although it is possible that these drainages may have experienced minor upstream flooding by May 19.

May 24-June 4, 2013: Seismic activity declined to near background levels and ash emissions were not observed prompting AVO to lower the Volcano Alert Level and Aviation Color Code to Advisory/Yellow on May 28.

June 4, 2013-present: On the late morning of June 4, seismic activity, satellite data, and pilot reports confirmed that ash emissions had resumed indicating that Pavlof was again erupting. AVO immediately raised the Volcano Alert Level and Aviation Color Code to Watch/Orange. Since then, seismic activity has been characterized by periods of intermittent volcanic tremor and slightly more robust and more frequent short-lived explosions compared to those observed during May 13-24. During this period, ash plumes have been generally small and have not extended beyond about 30 miles (50 km) downwind of the volcano. Since June 4, the maximum plume reported was approximately 20,000 ft. above sea level on June 10. Barely perceptible trace ash fall was reported in Cold Bay on June 6-7.

Seismic and satellite data combined with pilot reports and local observations indicate that Pavlof Volcano is experiencing a moderate eruption that is similar to past eruptions of this volcano. Periods of volcanic seismic tremor likely correspond to sustained episodes of lava fountaining and spatter accumulation high on the upper flank of the volcano and ash emissions. Occasionally, piles or heaps of accumulated spatter may collapse gravitationally and produce hot, clast-rich flows that can erode channels and melt snow and ice producing melt water that generates lahars. These flows may initiate steam plumes as they flow across snow and ice, which may be observed rising from areas lower on the flank of the volcano. Hot flows may also melt deep channels in the ice.

The explosion signals detected in seismic and infrasound data are likely the result of gas-rich slugs of magma bursting open as they reach the surface. At times the explosions may be powerful enough to spray lava into the air or produce episodic bursts of ash and gas. These events are short lived, lasting on the order of several seconds per event. There can be multiple such explosions per minute and this type of activity may persist for days to weeks.
At this time it is not known how long the eruption will continue or if it will intensify and become more explosive. Previous eruptions of Pavlof Volcano have lasted for weeks to months and occasionally have been associated with vigorous ash emissions and plumes that reached 30,000-50,000 ft.

So far, the eruption has generated mainly minor, low-level ash plumes that have not exceeded 22,000 ft. above sea level and residents in nearby communities have reported only trace amounts of ash fall, although thicker amounts of ash have likely accumulated on and around the volcano. At times, the persistent low-level eruptive activity results in a widespread, but relatively diffuse ash cloud that may be difficult to observe in marginal weather conditions. In clear weather, the ash plume should be visible to pilots and observers on the ground.

In past eruptions of Pavlof Volcano, lava fountaining from vents at or near the summit produced piles or heaps of lava spatter that either flowed gradually downslope, or collapsed suddenly producing fast-moving, clast-rich flows that typically resulted in snow and ice melt that lead to lahars and floods in affected drainages. In 1996, lahars reached the Bering Sea via the Leontovich River valley, and in 2007 lahars flowed to Pavlof Bay following drainages on the south flank of the volcano. If spatter production continues, it is likely that lahars will flow into the drainages that originate on the volcano's flanks and hazardous hydrologic conditions could occur in the Leontovich, Caribou, and upper Cathedral River valleys and possibly other drainages. These areas could be inundated by intermittent flows of water, mud and debris several feet or more deep.

At the present level of activity, more than a trace amount of ash fall (<1/32 inch) on nearby communities is unlikely. However, if activity were to intensify, areas downwind of the volcano may receive slightly more ash fallout. Information about mitigating the effects of volcanic ash fall can be found at http://volcanoes.usgs.gov/ash/ and procedures for reporting ash fall observations to AVO can be found on the AVO web page (www.avo.alaska.edu).
While Pavlof is active, it will be dangerous for pilots or individuals to approach the volcano closely. It is possible for activity levels to change suddenly and vigorous ash emission, lava fountaining and ballistic ejection of rock debris can occur with little or no warning. The hazards associated with eruptions of Pavlof are described in a hazard assessment for the area available on the AVO web page (http://www.avo.alaska.edu/downloads/reference.php?citid=4180).

Previous eruptions of Pavlof Volcano have lasted for weeks to months to years and often exhibit fluctuating levels of activity and it is not uncommon for the volcano to enter short periods of repose followed by vigorous ash emissions, lava fountaining, and lahar generation. Occasionally past eruptions have generated vigorous ash emissions and clouds that reached 30,000-50,000 ft. above sea level. We expect this eruption to proceed in a manner similar to previous eruptions.

AVO is monitoring the volcano closely and has been receiving information from pilots and local observers that helps to define the style of eruptive activity and extent of potential hazards. AVO's monitoring capabilities are however, degraded compared to prior eruptions as 4 seismic stations and 1 infrasound sensor of the network, are not operation at this time. At this point there is no evidence to indicate that the current eruption will differ from previous eruptions, and it would not be unusual for the volcano to remain intermittently active, behaving as it has for the past month, for several additional months or more. Thus, communities downwind of the volcano should be prepared for intermittent periods of trace ash fall. Additional information about Pavlof Volcano and the eruption are described in more detail on the AVO web page (www.avo.alaska.edu) or by calling AVO directly at 907-786-7497.

VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu

John Power, Scientist-in-Charge, USGS
jpower@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAFGI
jflarsen@alaska.edu (907) 474-7992

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.