ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 3, 2017, 1:19 PM AKST (Friday, March 3, 2017, 22:19 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

During the past week, no significant volcanic activity was detected in seismic, infrasound, or satellite data at Bogoslof.

There have been no explosive eruptions at the volcano since February 19. The current 12-day span without an explosive event is the longest observed since this eruptive sequence began in early December 2016. This longer repose may indicate that the eruption is waning. It is also possible that significant explosive eruptive activity could resume with little or no warning. A satellite image from February 23 shows the vent location at Bogoslof remains underwater, suggesting that if future explosive eruptive activity occurs, it will likely be similar in character to that observed over the past 2 months.

Seismic network outages from nearby Umnak Island have reduced AVO's seismic monitoring capabilities, limiting our ability to forecast or rapidly characterize Bogoslof activity. AVO continues to use infrasound (pressure) sensors from Umnak Island and will rely on seismic data from Unalaska Island to monitor Bogoslof, which will still allow for timely detection of significant activity. In addition, we use satellite imagery to track ash clouds and information from the Worldwide Lightning Location Network to identify volcanic lightning. 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.

In addition to the significant explosive events that we are able to detect, 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.

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: WATCH
Current Aviation Color Code: ORANGE

Slightly elevated surface temperatures were observed at the summit in nighttime infrared satellite images for the latter five days of this week. Minor steaming from the summit was visible in clear views from the web camera over the same period. No significant volcanic activity has been detected in seismic or infrasound data over the past week.

We have had no recent observations of the lava dome that began extruding in the summit crater in late January, and it is unclear whether it is still slowly growing. However, the dome's presence may act as a plug on the vent that restricts gas emissions, which could pressurize the system resulting in explosive activity with little to no warning.

Cleveland volcano is monitored with a limited real-time seismic network, which inhibits AVO's ability to detect precursory unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, lightning and satellite data.

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.

OTHER ALASKA VOLCANOES

Information on all Alaska volcanoes is available at : http://www.avo.alaska.edu.

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

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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