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U.S. Geological Survey
Thursday, August 5, 2021, 12:53 PM AKDT (Thursday, August 5, 2021, 20:53 UTC)

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. Over the past day, numerous earthquakes and small explosions have been recorded on local infrasound and seismic stations. This morning, local observers reported low-level lava fountaining at the active vent that was also visible from Adak Island. A robust volcanic cloud has been observed in web camera views of the volcano throughout the day today. This cloud is extending to the north-northeast below about 10,000 feet above sea level. It likely consists mostly of volcanic gas and water vapor but could include some amount of ash.

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.

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 characterized the unrest, similar to what has been detected over the past several days. Last night another small ash cloud was generated and was visible in satellite data from about 05:23 UTC 8/5/2021 (9:23 PM AKDT, 8/4/2021) until about 10:50 UTC, 8/5/2021 (02:50 AM AKDT). The ash cloud drifted to the southeast over Gareloi and southern Tanaga Island about 180 km before it was no longer visible in GOES-17 data. Ash emissions also were visible in web camera views of north crater yesterday evening. Satellite data confirmed that emissions of sulfur dioxide gas were occurring 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.

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.

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 observed this morning. Seismic tremor and small explosions have been detected by local seismic and infrasound instruments. The ash emissions observed this morning were limited in extent and likely produced only local fallout on the southeast flank of the volcano. The heightened level of unrest at Pavlof prompted AVO to raise the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH this morning.

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.


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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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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