ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, June 9, 2017, 1:25 PM AKDT (Friday, June 9, 2017, 21:25 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 continues. This week marked a change in activity at the volcano, with the appearance of a lava dome that breached the surface of the ocean on or around June 6. This is the first observation of lava at the surface since the start of the eruption sequence that began in mid-December 2016. The dome was estimated to be 110 m in diameter on Wednesday, June 7 and has grown to a diameter of 160 m as of this morning, June 9. Dome growth may be continuing at present, but we are unlikely to observe many of the seismic signals associated with lava effusion given the lack of near-by seismic instruments. Four short-duration explosions were detected in seismic and/or infrasound data between Monday and Wednesday and generated volcanic clouds that in many cases were too small to be observed in satellite data. Robust steaming has been observed in satellite data and by a USF&WS ship in the region following the emergence of the lava dome and is likely due to, or enhanced by, the effusion of lava into the ocean.

Some past eruptive sequences of Bogoslof have ended with the emplacement of a lava dome, but in other cases, lava effusion has been followed by additional explosive eruptions. If future explosive eruptions do occur, the resulting volcanic cloud could be more ash-rich than those that have occurred thus far in the sequence that began in 2016. Low-level eruptive activity may 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. A Temporary Flight Restriction (TFR) is in effect over the volcano at the present time. Please see http://tfr.faa.gov/tfr2/list.html for the status of the TFR.

We continue to use infrasound (pressure) sensors from nearby Umnak Island and other sites and seismic data from Umnak and Unalaska Islands 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 generated in ash clouds.

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

Unrest continues at Cleveland. There was evidence of possible lava effusion within the summit crater during this past week. Small low-frequency earthquakes were detected in seismic data on Tuesday, June 6 and elevated surface temperatures were observed in night-time satellite images on Wednesday, June 7. No explosive activity from Cleveland Volcano was observed during the week.

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.

PAVLOF VOLCANO (VNUM #312030)
55°25'2" N 161°53'37" W, Summit Elevation 8261 ft (2518 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

The Aviation Color Code for Pavlof Volcano was raised to YELLOW on Wednesday, June 7 following an increase in low-frequency seismic activity and a pilot report indicating a possible ash cloud to 4000 ft asl. Active degassing from the summit was observed in web camera images and by local observers in Cold Bay yesterday and this morning. Infrasound data from local instruments on Pavlof and a more distant network in Sand Point show no evidence of significant explosive activity during the past week. Seismic activity has been at background levels since Thursday, June 8. Precursory activity leading up to previous explosive eruptions at Pavlof have been subtle and while some episodes of increased seismic activity have preceded eruptive episodes other increases have died back down without explosive activity.

Vapor emissions, with or without minor amounts of volcanic ash, are common and may occur from the summit vent at any time. Periods of more vigorous ash emission and lava fountaining also are possible and could occur with only subtle changes in the level of seismic activity. Pavlof is one of the most frequently active volcanoes in Alaska, and pauses in eruptive activity followed by renewed unrest and ash emission are common.

Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 953 km (592 mi) southwest of Anchorage. The volcano is about 7 km (4.4 mi) in diameter and has active vents on the north and east sides close to the summit. With over 40 historic eruptions, it is one of the most consistently active volcanoes in the Aleutian arc. Eruptive activity is generally characterized by sporadic Strombolian lava fountaining continuing for a several-month period. Ash plumes as high as 49,000 ft ASL have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 feet above sea level were generated and the ash was tracked in satellite data as distant as eastern Canada. The nearest community, Cold Bay, is located 60 km (37 miles) to the southwest of Pavlof.

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

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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