ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 10, 2017, 1:18 PM AKST (Friday, March 10, 2017, 22:18 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

The eruption of Bogoslof volcano continued over the past week. Currently, an earthquake swarm that developed overnight March 9-10 is ongoing at Bogoslof. This swarm follows a significant, 3-hour-long explosive event that occurred overnight March 7-8. The current earthquake swarm began at 2:50 UTC March 10 (17:50 AKST March 9) and has been ongoing for over 19 hours. Coincident with the ongoing earthquake swarm, satellite data from this morning indicate mildly elevated surface temperatures at Bogoslof. Taken together with the observed earthquake swarm, the satellite data suggest a lava dome may be forming at the volcano. AVO is monitoring the current activity closely and will provide updates as warranted.

The 3-hour-long explosive event that occurred overnight March 7-8 produced numerous strokes of volcanic lightning, high levels of seismicity and infrasound, and an ash cloud up to 35,000 ft that moved eastward over Unalaska Island. The seismicity was among the highest levels observed for the current eruption sequence that began in mid-December 2016, and the more than 1000 detected lightning strokes were by far the highest number observed to date. Trace amounts of ashfall were forecast for Unalaska Island, although reports from the community of Unalaska/Dutch Harbor suggest negligible ashfall and air quality data did not show elevated concentrations of particulate matter at the expected time of ashfall. The eruptive activity also changed the shape of the island and temporarily dried out the vent area. After the event, satellite data showed the west coast of the island appeared to have grown significantly due to the eruption of new volcanic ash and blocks. A new vent was also identified on the northwest side of the island and the lava dome emplaced during the 1992 Bogoslof eruption was partially destroyed.

Depending on the intensity of any future activity, the presence of water in the vent area may lead to enhanced fallout of ash from the volcanic cloud. More intense eruptions such as the event overnight March 7-8, however, may again build the vent up so that it is above sea level. The nature of future volcanic activity may shift accordingly, perhaps switching between short events with ice-rich clouds to longer, more ash-rich events.

The possible formation of lava dome at Bogoslof is consistent with observations of prior eruptions of the volcano. Sometimes lava domes form at the end of an explosive eruption sequence, but at other times additional explosions may destroy a dome. Thus if a new dome is forming, it is not currently clear what impact that would have on the probability of future explosive eruptive events.

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: ADVISORY
Current Aviation Color Code: YELLOW

Slightly elevated surface temperatures were observed at the summit on four days of this week. Minor steaming from the summit was visible in clear views from the web camera once over the same period. No significant volcanic activity has been detected in seismic or infrasound data over the past week.

Based on a continuation of low seismic levels, and no observations nor reports of continued eruptive activity in the summit crater, AVO on Wednesday reduced the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY at Cleveland volcano. The slightly elevated temperatures that were observed this week are consistent with cooling of the lava dome that formed in late January 2017.

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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