ALASKA VOLCANO OBSERVATORY DAILY UPDATE
U.S. Geological Survey
Wednesday, March 8, 2017, 1:54 PM AKST (Wednesday, March 8, 2017, 22:54 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

The eruption of Bogoslof volcano continues. Volcanic ash emissions have ceased following the explosive event that began last night at 22:36 AKST (7:36 UTC, March 8) and continued for over three hours. The event was detected by high levels of seismic tremor and explosive pressure waves in the atmosphere, as measured by sensors on neighboring Unalaska and Umnak Islands, as well as by numerous lightning strokes. The resulting ash cloud was tracked in satellite data for more than 12 hours, and moved towards the east over Unalaska Island at an altitude of approximately 35,000 ft above sea level. Trace amounts of ashfall were forecast for Unalaska Island, although reports from the community of Unalaska/Dutch Harbor this morning suggest negligible ashfall and air quality data do not show elevated concentrations of particulate matter at the expected time of ashfall.

Last night's event was the first detected eruptive activity at Bogoslof since February 19. The seismicity was among the highest levels observed for the current eruption sequence that began in Mid-December 2016, and more than 1000 lightning strokes related to the volcanic eruption cloud were detected during this event, by far the highest number observed to date.

Satellite images from earlier today show changes at Bogoslof Island following the recent activity. The west coast of the island appears to have grown significantly due to eruption of new volcanic ash and blocks. Furthermore, whereas most explosive events in this sequence have issued from a vent in shallow seawater, the vent area now appears to be dry as a result of the eruptive activity. We do not expect the vent area to remain dry, as seawater will likely infiltrate the crater walls and again flood the vent. Eruptions during periods when the vent is not submerged (or dry) effect the character of the seismic and infrasound signals, and may generate volcanic clouds that are more ash-rich (with less ice formation).

Although detectable seismic activity is currently at low levels, Bogoslof volcano remains at a heightened state of unrest and in an unpredictable condition. Additional explosions producing high-altitude volcanic clouds could occur at any time. The Aviation Color Code remains at RED and the Volcano Alert Level at WARNING. We will continue to evaluate monitoring data throughout the day to determine whether a decrease in alert levels are warranted.

Some previous explosions have been preceded by an increase in earthquake activity that allowed for short-term forecasts of imminent significant explosive activity. Although we are able to detect energetic 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. Low-level explosive activity that is below our ability to detect in our data sources may be occurring. These low-level explosions could pose a hazard in the immediate vicinity of the volcano.

AVO has no ground-based volcano monitoring equipment on Bogoslof volcano. We continue to monitor satellite images, information from the Worldwide Lightning Location Network pertaining to volcanic-cloud lightning, and data from seismic and infrasound instruments on nearby islands for indications of volcanic activity.

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

No activity was observed in cloudy satellite images and cloudy web camera views over the past day. No significant volcanic activity has been detected in seismic or infrasound data.

Based on a continuation of low seismic levels, and no observations nor reports of continued eruptive activity in the summit crater, AVO earlier today reduced the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY at Cleveland volcano.

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.

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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