ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 14, 2017, 2:21 PM AKDT (Friday, July 14, 2017, 22:21 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

Several eruptive episodes occurred over the past week, twice prompting AVO to raise the Aviation Color Code to RED and the Volcano Alert Level to WARNING. On the morning of Saturday, July 8, an eruption with a total duration of 19 minutes began at 10:15 AKDT (18:15 UTC) and produced a volcanic cloud reaching an altitude of 30,000 ft above sea level (asl) that was carried to the north. The Aviation Color Code/Volcano Alert Level was reduced to ORANGE/WATCH the following day. Overnight Sunday July 9 and into early Monday, July 10, Bogoslof erupted several times over the course of 3 hours, prompting AVO to raise Aviation Color Code/Volcano Alert Level to RED/WARNING. The first two explosions during the 3-hour-long eruption produced a small volcanic cloud reaching an altitude of 20,000 ft asl that was carried to the southeast and dissipated rapidly. About 5 hours after the end of the eruption, AVO reduced the Aviation Color Code/Volcano Alert Level to ORANGE/WATCH. Later on Monday July 10, Bogoslof had an 8-minute-long eruption beginning at 10:00 AKDT (18:00 UTC) and a 15-minute-long eruption beginning at 17:06 AKDT (01:06 UTC July 11). Neither of these two eruptions produced a significant volcanic cloud and the Aviation Color Code/Volcano Alert Level remained at ORANGE/WATCH. None of the eruptions over the past week caused ashfall in local communities. Since the eruptions on Monday, no activity has been detected in seismic, infrasound, or lightning data. Weakly elevated surface temperatures were observed at Bogoslof in clear satellite images on Tuesday July 12.

Volcanic explosions producing high-altitude (>15,000 ft) volcanic clouds with little or no warning remain possible. 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 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

No explosive activity was detected at Cleveland Volcano this week. Moderately elevated surface temperatures were observed in satellite images on one day of the week (July 14), and occasional clear views of the summit in the web camera showed only light steaming. No activity has been observed in seismic or infrasound data over the past week.

A data outage for stations at the volcano continues since 2:00 am AKDT (10:00 UTC) on July 12. Explosive activity at Cleveland can be detected by distal stations in the AVO network, but at a reduced level of sensitivity. Web camera views have also been unavailable since the outage began.

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

Elevated surface temperatures were observed in satellite images on July 12 and 13 at Pavlof during the past week. Minor vapor plumes have been observed extending from the summit on several days this week when web camera views were clear. Nothing significant was observed in seismic or infrasound data.

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:

Peter Cervelli, Acting Scientist-in-Charge, USGS
pcervelli@usgs.gov (907) 786-7424

Janet Schaefer, Acting Coordinating Scientist, DGGS
janet.schaefer@alaska.gov (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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