ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 17, 2017, 2:39 PM AKST (Friday, February 17, 2017, 23:39 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. The most recent explosive eruption from the volcano occurred this morning starting at about 9:56 AKST (18:56 UTC) and was observed by seismic, infrasound, and lightning data. Satellite images and pilot reports indicate that the resulting ash cloud reached as high as 38,000 ft asl. Winds carried the cloud northward from Bogoslof out over the Bering Sea. This morning's activity, which consisted of individual pulses as seen in seismic data, lasted until about 11:40 AKST (20:40 UTC). Since then, seismicity as detected on neighboring islands has been low. In response to today's activity, AVO raised the Aviation Color Code to RED and the Alert Level to WARNING.

Before this morning, the last probable explosive event from Bogoslof occurred on Monday, February 13, starting at 7:24 AKST (16:24 UTC). Monday's activity was characterized by strong seismicity, but was not detected in infrasound nor lightning data. No volcanic cloud was detected in satellite images above weather clouds, which were at about 10,000 ft asl at the time. These observations suggest that despite the strong seismicity on Monday, the unrest that day did not result in significant ash emissions.

The frequency of explosive events has been lower over the past two weeks than it had been earlier in the eruptive sequence, but today's activity shows that significant eruptions are still possible. AVO continues to use seismic and infrasound (pressure) sensors on neighboring Umnak and Unalaska Islands to monitor 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

No significant activity was observed in satellite or web camera views this week, though the volcano was almost entirely obscured by clouds. No significant volcanic activity has been detected in seismic or infrasound data over the past week.

We have had no additional observations of the lava dome that began extruding in the summit crater in late January.

Cleveland volcano is not monitored with a real-time seismic network and this inhibits AVO's ability to detect unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of satellite, infrasound, lightning data and local observations.

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

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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