ALASKA VOLCANO OBSERVATORY DAILY UPDATE
U.S. Geological Survey
Sunday, August 8, 2021, 1:35 PM AKDT (Sunday, August 8, 2021, 21:35 UTC)

GREAT SITKIN VOLCANO (VNUM #311120)
52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Elevated seismic activity continues at Great Sitkin volcano. A possible minor explosion was detected in infrasound data over the past day although no corresponding seismic signals were observed. Elevated surface temperatures and minor volcanic clouds (most likely water vapor and volcanic gas) were observed in a few satellite images over the past day. The elevated surface temperatures are a result of lava effusion within the summit crater that has been ongoing for nearly two weeks.

Occasional explosive activity, continued lava effusion, or both remain possible outcomes of the current period of unrest. The duration of unrest is uncertain. Great Sitkin volcano is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

SEMISOPOCHNOI VOLCANO (VNUM #311060)
51°55'44" N 179°35'52" E, Summit Elevation 2625 ft (800 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Explosions and elevated seismicity at north crater on Semisopochnoi Island continue. An explosion at 14:53 UTC today (06:53 AKDT) generated a large infrasound signal but no significant corresponding ash emissions were detected in satellite data although viewing conditions have been hampered by thick cloud cover. A small possible ash cloud was apparent in one GOES-17 image from 15:00 UTC, but was no longer discernible by 15:10 UTC. Seismic tremor continues but appears to have waned somewhat. Sulfur dioxide emissions from the volcano also were evident in satellite data over the past day.

Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds under 10,000 feet above sea level have characterized the recent activity and show no signs of abating. Small explosions may continue and could be difficult to detect in seismic, infrasound, satellite, and web camera data, especially in poor weather conditions.

Semisopochnoi is monitored by local seismic and infrasound sensors, satellite data, regional infrasound, and lightning detection instruments.

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

Slight unrest continues at Cleveland volcano. Seismicity has been at low levels over the past day and no evidence of explosive activity was detected in seismic or regional infrasound data. The volcano has been obscured by clouds and there were no outward signs of activity noted in satellite or web camera data over the past day.

Episodes of lava effusion and explosions can occur without advance warning. Explosions from Cleveland are normally short duration and only present a hazard to aviation in the immediate vicinity of the volcano. Larger explosions that present a more widespread hazard to aviation are possible, but are less likely and occur less frequently.

When operational, Cleveland volcano is monitored by only two seismic stations, which restricts AVO's ability to precisely locate earthquakes and 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.

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

Unrest continues at Pavlof volcano and minor ash emissions to just above the summit of the volcano were again observed yesterday afternoon. Elevated seismic activity (tremor) continues but no explosions have been detected over the past 16 hours. The ash emissions observed yesterday were limited in extent and only visible in one web camera image from 15:08 AKDT (23:08 UTC, 8/7/2021). The ash burst likely produced only local fallout on the southeast flank of the volcano.

The level of unrest at Pavlof can change quickly and the progression to significant eruptive activity can occur with little or no warning. AVO continues to monitor Pavlof closely and will provide any new information about the status of the volcano when or if it becomes available.

Pavlof is monitored by local seismic and infrasound sensors, satellite data, web cameras, and distant infrasound and lightning networks.

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/

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CONTACT INFORMATION:

Matt Haney, Acting Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAF dfee1@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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