ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, September 1, 2017, 12:13 PM AKDT (Friday, September 1, 2017, 20:13 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

Unrest continues at Bogoslof. Five short-lived explosive eruptions occurred during the past week. The first occurred 16:29 AKDT on August 26 (00:29 UTC on August 27) and produced an eruption cloud that reached to 25,000–30,000 ft. This was followed by explosions at 15:08 AKDT (23:08 UTC) on August 27 and at 3:23 and 11:17 AKDT (11:23 and 19:17 UTC) on August 28 that produced eruption clouds that also reached to 25,000–30,000 ft. The final explosive event of the week occurred at 4:05 AKDT (12:05 UTC) on August 30 and produced an eruption cloud that reached to about 20,000 ft. The clouds from these events were typically small in size, despite reaching fairly high altitudes, and dispersed quickly. Thus, the Aviation Color Code remained at Orange and the Volcano Alert Level at Watch throughout.

Available data suggest that lava is currently present at the surface within the intra-island lake just west of the 1992 lava dome. Elevated surface temperatures were observed intermittently early in the week, and occasional plumes (most likely composed of water vapor) were observed extending from Bogoslof Island.

Volcanic explosions producing high-altitude (>15,000 ft asl) volcanic clouds remain possible with little or no warning. 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 can be a lag of tens of minutes until we can characterize the magnitude of the event and the altitude of the volcanic cloud.

With existing data sources, AVO may not detect low-level unrest, including minor explosive activity. Such low-level periods of unrest and possible explosions could pose hazards near the volcano. A Temporary Flight Restriction (TFR) remains in effect over the volcano. Please see http://tfr.faa.gov/tfr2/list.html for the status of the TFR.

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

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 Volcano. Nothing unusual was detected in seismic or infrasound data over the past week. However, elevated surface temperatures observed sporadically in satellite data suggest that lava is present at the surface within the volcano's summit crater. A weak vapor plume was sometimes visible at the summit in webcam images as well.

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: NORMAL
Current Aviation Color Code: GREEN

Low-level unrest continues at Pavlof, but no significant activity was observed in geophysical or satellite data during the past week. This low level of activity is now considered as being indicative of normal, non-eruptive behavior at Pavlof. For this reason, the Aviation Color Code was changed to Green and the Volcano Alert Level was changed to Normal on August 30.

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

SUBSCRIBE TO VOLCANO ALERT MESSAGES by email: http://volcanoes.usgs.gov/vns/

FOLLOW AVO ON FACEBOOK: https://facebook.com/alaska.avo

FOLLOW AVO ON TWITTER: https://twitter.com/alaska_avo

CONTACT INFORMATION:

Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAFGI
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.

---