ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, January 27, 2017, 4:58 PM AKST (Saturday, January 28, 2017, 01:58 UTC)

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

Volcanic unrest at Bogoslof continues. There were five significant explosive events this week: on January 20 at 22:17 UTC (13:17 AKST), January 22 at 23:09 UTC (14:09 AKST), January 24 at 13:53 UTC (4:53 AKST), January 26 at 15:50 UTC (6:50 AKST) and January 27 at 17:24 UTC (8:24 UTC). These explosions produced volcanic clouds that rose as high as 36,000 ft above sea level and were discernible in satellite images for hours afterwards. These clouds were ice-rich, due to the influx of seawater into the eruption column, but likely contained volcanic ash as well. Several of the volcanic clouds have been transported by prevailing wind towards Unalaska/Dutch Harbor, but there were no reports of volcanic ash fallout in that community.

Some of these explosions were preceded by an increase in earthquake activity, recorded on seismic networks on adjacent volcanoes, that allowed for short-term forecasts of imminent significant explosive activity. It is likely that lower-level explosive activity is occurring that is below our ability to detect in our data sources. These low-level explosions could pose a hazard in the immediate vicinity of the volcano. Although we are able to detect significant explosive activity in real-time, there is typically a lag of tens of minutes until we can characterize the magnitude of the event and the altitude of the volcanic cloud.

A high spatial-resolution satellite image collected on January 24 shows that the explosive eruptions continue to change the morphology of the island and the coastline. The eruptive vent remains below sea level in the northern portion of a figure-eight-shaped bay, as indicated by the presence of upwelling volcanic gases. There is no sign of lava at the surface.

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 (pressure 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. No activity observed in satellite images this week. Clear views of the summit in web camera images on January 21 showed minor steaming 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.

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.

TAKAWANGHA VOLCANO (VNUM #311090)
51°52'1" N 178°1'37" W, Summit Elevation 4754 ft (1449 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

The seismic swarm that began at Takawangha Volcano on January 23 has significantly decreased in the last day. Occasional earthquakes continue, but the rate at which these events are occurring has been steadily decreasing from a peak of 190 located events on January 24 to 22 today. Most of the events are located 7-8 km ESE of Takawangha and at shallow depths. Similar seismic swarms were detected on Tanaga Island in 2005, 2008 and 2009. In 2005, a small phreatic eruption is believed to have occurred from Takawangha Volcano but the activity was only seen in seismic data and not verified by satellite data or visual observations. It is likely that there would be an increase from the current seismic levels prior to a new eruption at Takwangha Volcano. It is also possible that the current activity will cease with no eruption from the volcano.

Takawangha is a remote, 1,449 m (4,754 ft)-high stratovolcano located on the northeast portion of Tanaga Island, roughly 95 km (59 miles) west of Adak in the Andreanof Islands. Takawangha's summit is mostly ice-covered, except for four young craters that have erupted ash and lava flows in the last few thousand years. Parts of Takawangha's edifice are hydrothermally altered and may be unstable, possibly leading to localized debris avalanches from its flanks. Takawangha lies across a saddle from historically active Tanaga volcano to the west. No historical eruptions are known from Takawangha; however, field work shows that recent eruptions have occurred and it is possible that historic eruptions attributed to Tanaga may instead have come from Takawangha.

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

Jessica Larsen, Acting Coordinating Scientist, UAF
jflarsen@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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