ALASKA VOLCANO OBSERVATORY DAILY UPDATE
U.S. Geological Survey
Wednesday, August 4, 2021, 12:43 PM AKDT (Wednesday, August 4, 2021, 20:43 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

Unrest continues at Great Sitkin volcano. No explosive activity was observed in seismic or infrasound data. Seismicity remains elevated and steady with no appreciable changes over the past day. Occasional slightly clear web camera views from Adak this morning showed nothing noteworthy occurring at the active vent.

Renewed explosive activity or lava effusion remain possible outcomes of the current period of unrest. This is not certain and a decline in unrest to background levels of activity is also possible. 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

Unrest continues at Semisopochnoi volcano. Detection of multiple, discrete, energetic explosion signals on local seismic and infrasound stations has again characterized the unrest over the past day. Last night there were multiple brief explosions and a small ash cloud was generated. The ash cloud was visible in satellite data until about 13:17 UTC, August 4, 2021 (05:17 AKDT) and at that time was about 33 km (20 mi) northeast of Semisopochnoi Island. Satellite based estimates indicate a maximum ash cloud height of 5,000 - 10,000 feet (1.5 - 3 km) above sea level. Ash emissions were visible in web camera views of north crater and photographed by a local observer south of Semisopochnoi Island. As of about 08:30 AM AKDT this morning, significant emissions were no longer evident in web camera views. Satellite data also confirmed that emissions of sulfur dioxide gas were ocurring 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 ft above sea level are typical of recent activity at Semisopochnoi. Small explosions may occur without warning and could be undetected by regional infrasound sensors and cloudy 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: ADVISORY
Current Aviation Color Code: YELLOW

Unrest continues at Pavlof volcano. Seismic tremor continues to be detected but no evidence of explosive activity was observed in seismic or infrasound data. No activity was observed in mostly cloudy satellite and occasional clear web camera views.

The level of unrest at Pavlof can change quickly and the progression to 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/

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

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

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.

---