ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, December 23, 2016, 2:01 PM AKST (Friday, December 23, 2016, 23:01 UTC)
53°55'38" N 168°2'4" W,
Summit Elevation 492 ft (150 m)
Current Volcano Alert Level: WARNING
Current Aviation Color Code: RED
Bogoslof is in an active eruption sequence. On December 20, a powerful, short-lived explosion occurred at about 15:35 AKST (00:35 UTC Dec 21) that sent ash to over 30,000 ft asl. After a day of relative quiescence, another explosion occurred December 21 at 16:10 AKST (01:10 UTC Dec 22) as seen in satellite images and seismic data from neighboring islands. This eruption lasted about 30 minutes and sent ash as high as 35,000 ft asl. These first two eruptions dramatically altered Bogoslof Island and a new vent appears to have developed at the northeast end of the island, immediately offshore. This morning, a third strong ash-producing explosive eruption occurred at about 09:30 AKST (18:30 UTC). During today's event, observers aboard a Coast Guard vessel reported ash emission, lightning, and the ejection of incandescent lava and fragmental material. Ash emission and lava ejection subsided after about an hour, at 10:37 AKST (19:37 UTC). The ash cloud was carried northward over the Bering Sea and did not penetrate above the regional cloud tops at 30,000 ft. Elevated seismicity continues; however, signals are affected by a strong storm that moved across the Aleutian Islands in the past 24 hours.
Retrospective analysis of seismic, air-wave, and satellite data reveal that Bogoslof showed signs of unrest as early as December 12. Ash emissions may have occurred on December 16 and 19 on the basis of recorded lightning strikes, seismic data, and sulfur dioxide clouds detected in satellite, though there were no direct visual observations from satellite or ground observers.
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 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 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-high (492 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.
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 satellite images this week. One clear web camera view on Wednesday, December 21 showed minor steam emissions from the summit. 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.
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 significant activity was observed in satellite or web camera images during the week.
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
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Michelle Coombs, Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
Janet Schaefer, Acting Coordinating Scientist, DGGS
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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.