ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, January 20, 2017, 5:56 PM AKST (Saturday, January 21, 2017, 02:56 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

Volcanic unrest at Bogoslof continues. Explosive eruptions were detected this week on January 14 at 22:16 AKST (07:16 January 15 UTC), January 17 at 4:00 and 7:40 AKST (15:00 and 16:40 UTC), January 18 at 13:20 AKST (22:20 UTC) and January 20 at 13:17 AKST (22:17 UTC).

The January 18 event produced a dark ash cloud that pilots reported at at least 31,000 ft asl. This cloud was darker in color, and presumably more ash-rich, than others we have seen in the eruptive sequence, which began in mid-December 2016. This image also suggests the presence of very hot material (potentially lava) at the surface immediately surrounding the vent – the first such observation during this eruption sequence. This was also the first eruption since the 31 December 2016 event to produce detectable SO2 in satellite data, suggesting that fresh magma was involved in the eruption. This event also produced lightning strikes, and infrasound signals detected by sensors in Sand Point and Dillingham.

Analysis of satellite images from January 16 and 18 (before the eruption that day) show that the vent area that formed on the northeast end of the island in shallow seawater has been filling in and building out of the water. A more ash-rich cloud and the possibility of lava at the surface are consistent with a vent that is near, or above, sea level and interacting less with water.

The January 20 eruption reached a pilot-reported height of 36,000 ft asl. Prevailing winds carried it to the southeast over the southwest end of Unalaska Island, but no ash fall was reported. A satellite image of the cloud indicates that it was ice-rich, and also suggests that hot material (possibly lava) was present at the surface near the vent minutes after the eruption was detected in seismic data. This eruption also produced a single lightning strike, and infrasound signals detected by sensors in Dillingham.

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. AVO will continue to provide timely warnings of activity to the best of our ability and will issue Volcanic Activity Notices (VANs) and Volcanic Observatory Notices for Aviation (VONAs) as needed.

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

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 Aleutian Maritime Wildlife Refuge and is habitat for marine mammals and seabirds.

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. Nothing of note has been observed in satellite images this week. Clear views of the summit in web camera images on January 15-19 showed low-level steam plumes emanating from the summit crater. 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. No activity observed in mostly cloudy satellite images. Clear web camera views of the volcano on January 19 showed minor degassing from the summit and a diffuse vapor plume extending downwind.

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

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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