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ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, May 19, 2017, 1:37 PM AKDT (Friday, May 19, 2017, 21:37 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

Following a pause in explosive activity that lasted a little over two months, Bogoslof erupted explosively Tuesday night (May 16) at 22:32 AKDT (06:32 May 17 UTC). The eruption, which lasted about 70 minutes, was detected by seismic and infrasound sensors on neighboring islands and the resulting ash cloud generated volcanic lightning that was detected by the Worldwide Lightning Location Network. A pilot report and satellite images showed that the plume rose as high as 36,000 ft asl, and then drifted to the southwest. Trace ashfall was reported in the community of Nikolski on Umnak Island. A drifting sulfur dioxide cloud from the eruption was detected for several days using satellite-based sensors. The eruption altered the northern coastline of the island, with the crater lake now breached by a 550 meter-wide gap along the north shore. Part of the northeast shore has been extended 300 meters due to new tephra deposits.

As with the majority of the 38 explosive events that have occurred during Bogoslof's current eruptive sequence, Tuesday night's event was not preceded by measurable precursory seismic activity. The distance between Bogoslof and the nearest monitoring stations limits our ability to detect more subtle signals that may have preceded the eruption.

After the eruption, detected seismicity has returned to low levels. No other activity was observed throughout the week.

Though the volcano is currently quiet, renewed activity could occur at any time and could include additional explosive events and/or effusion of a lava dome. Lower-level eruptive activity may also occur that is below our ability to detect in seismic, infrasound, or satellite data sources, and could generate hazardous phenomena in the immediate vicinity of the volcano.

We continue to use infrasound (pressure) sensors from Umnak Island and seismic data from Unalaska Island to monitor Bogoslof, which allow for timely detection and sometimes forecasting 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.


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 2016-17, 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

An short explosive eruption occurred at Cleveland volcano Tuesday evening (May 16) at 19:17 AKDT (03:17 May 17 UTC). The eruption was detected by local seismic instruments and lasted about 11 minutes. The resulting ash cloud rose to about 15,000 feet above sea level and was seen in satellite images to drift to the southwest for about 5 hours.

Satellite observations show that the lava dome that had occupied the bottom of the summit crater was completely destroyed during Tuesday's eruption. This dome had formed following the previous eruption on March 8, 2017.

Conditions have been mostly cloudy over the past week, however, occasional clear webcam views of the summit have shown steam emissions.

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.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php

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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.