ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, December 30, 2016, 12:53 PM AKST (Friday, December 30, 2016, 21:53 UTC)

BOGOSLOF VOLCANO (VNUM #311300)
53°55'38" N 168°2'4" W, Summit Elevation 492 ft (150 m)
Current Volcano Alert Level: WARNING
Current Aviation Color Code: RED

Eruptive activity at Bogoslof continues. Last night at 23:45 AKST (08:45 Dec 30 UTC), another explosion occurred that lasted for about 30 minutes and produced a cloud that rose as high as 20,000 ft asl and drifted northeast as seen in satellite images. Last night's event was first detected by seismic stations on neighboring Umnak Island, and was also seen in more distant infrasound sensors. This event did not produce volcanic lightning. This morning, low-level seismic activity from the volcano was detected brielfy from 04:25 to about 05:00 AKST. The explosive event last night was preceded by as much as four and a half hours of elevated seismic activity from Bogoslof, providing some indication that an explosive eruption was imminent. Other explosions during the eruptive sequence have started more suddenly with either subtle or no preceding increase in seismicity.

Last night's event was the fourth explosion in the past week and eighth such explosion that AVO has detected since December 16. The explosions have occurred every 1-3 days. Given this pattern, the likelihood of another explosion in the next day remains high, and the Aviation Color Code remains at RED and the Volcano Alert Level at WARNING.

For more details about the current eruption, monitoring efforts, and information about the volcano's previous eruptions and possible hazards, please refer to yesterday's Information Statement (http://avo.alaska.edu/activity/report.php?need=current&id=350341&type=1&mode=hans ).

Bogoslof is not monitored by a local geophysical network, which limits our ability to forecast and closely track activity at this volcano. AVO is using seismic and infrasound (airwave sensors) on neighboring Umnak and Unalaska Islands to monitor activity. In addition, we are using satellite imagery and information from the Worldwide Lightning Location Network to identify volcanic lightning; lightning strikes in the erupted plume have been detected during the current eruptive sequence.

Bogoslof Island is the largest of a cluster of small, low-lying islands making up the emergent summit of a large submarine stratovolcano. The highest point above sea level prior to this eruption was about 100 m (300 ft); however, the volcano is frequently altered by both eruptions and wave erosion and has undergone dramatic changes in historical time. The two main islands currently above sea level are Fire Island and Bogoslof Island, both located about 98 km (61 mi) northwest of Unalaska/Dutch Harbor, 123 km (76 mi) northeast of Nikolski, and 149 km (93 mi) northeast of Akutan. The volcano is situated slightly north (behind) the main Aleutian volcanic front. Bogoslof volcano is within the USFWS Maritime Wildlife Refuge and is habitat for sea lions birds.

At least 8 historical eruptions have been documented at Bogoslof. The most recent prior to 2016 occurred from July 6-24, 1992, and produced episodic steam and ash emissions including an ash cloud up to 26,000 ft (8 km) asl on July 20, followed the next day by extrusion of a new 150 m (500 ft) by 275 m (900 ft) lava dome on the north end of the island. Previous eruptions of the volcano have lasted weeks to months, and have on occasion produced ash fall on Unalaska. Eruptions of the volcano are often characterized by multiple explosive, ash-producing events such as we have seen in 2016, as well as the growth of lava domes.

CLEVELAND VOLCANO (VNUM #311240)
52°49'20" N 169°56'42" W, Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Low-level unrest continues at Mt. Cleveland. No activity was observed in occasional clear satellite views this week, and the web camera is currently not returning data. No activity was detected in seismic or infrasound (pressure sensor) data all week.

Cleveland volcano forms the western portion of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. The volcano is located about 75 km (45 mi) west of the community of Nikolski, and 1500 km (940 mi) southwest of Anchorage. The most recent significant period of eruption began in February, 2001 and produced 3 explosive events that generated ash clouds as high as 39,000 ft above sea level. The 2001 eruption also produced a lava flow and hot avalanche that reached the sea. Since then, Cleveland has been intermittently active producing small lava flows, often followed by explosions that generate small ash clouds generally below 20,000 ft above sea level. These explosions also launch debris onto the slopes of the cone producing hot pyroclastic avalanches and lahars that sometimes reach the coastline.

PAVLOF VOLCANO (VNUM #312030)
55°25'2" N 161°53'37" W, Summit Elevation 8261 ft (2518 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Low-level unrest continues at Pavlof Volcano. Seismic activity remains slightly above background. Clouds and snow obscured views of Pavlof in satellite and web camera images, respectively, for most of the week, but elevated surface temperatures were observed in satellite data on December 29, which coincided with a summit steam plume visible in web camera images that day.

Vapor emissions, with or without minor amounts of volcanic ash, are common and may occur from the summit vent at any time. Periods of more vigorous ash emission and lava fountaining also are possible and could occur with only subtle changes in the level of seismic activity. Pavlof is one of the most frequently active volcanoes in Alaska, and pauses in eruptive activity followed by renewed unrest and ash emission are common.

Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 953 km (592 mi) southwest of Anchorage. The volcano is about 7 km (4.4 mi) in diameter and has active vents on the north and east sides close to the summit. With over 40 historic eruptions, it is one of the most consistently active volcanoes in the Aleutian arc. Eruptive activity is generally characterized by sporadic Strombolian lava fountaining continuing for a several-month period. Ash plumes as high as 49,000 ft ASL have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 feet above sea level were generated and the ash was tracked in satellite data as distant as eastern Canada. The nearest community, Cold Bay, is located 60 km (37 miles) to the southwest of Pavlof.

OTHER ALASKA VOLCANOES

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

FOR MORE INFORMATION ON ALASKA VOLCANOES: http://www.avo.alaska.edu

SUBSCRIBE TO VOLCANO ALERT MESSAGES by email: http://volcanoes.usgs.gov/vns/

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CONTACT INFORMATION:

Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

Janet Schaefer, Acting Coordinating Scientist, DGGS
janet.schaefer@alaska.gov (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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