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U.S. Geological Survey
Friday, February 22, 2019, 1:23 PM AKST (Friday, February 22, 2019, 22:23 UTC)

52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Low level unrest is continuing at Great Sitkin Volcano. Nothing significant was observed in satellite data this week, but several small earthquakes have been detected on local seismic stations throughout the week, normally a few each day. A regional infrasound array on Adak Island did not pick up any indications of explosive activity.

Great Sitkin Volcano is monitored with a local real-time seismic network, which will typically allow AVO to detect changes in unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption would be accomplished using a combination of seismic, infrasound, lightning, and satellite data.

Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 43 km (26 miles) east of the community of Adak. The volcano is a composite structure consisting of an older decapitated volcano and a younger parasitic cone with a 2-3 km diameter summit crater. A steep-sided lava dome, emplaced during an eruption in 1974, occupies the center of the crater. Great Sitkin erupted at least three times in the 20th century, most recently in 1974. That eruption produced a lava dome and at least one ash cloud that likely exceeded an altitude of 25,000 ft above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.

56°11'52" N 159°23'35" W, Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Slightly elevated surface temperatures consistent with cooling lava flows were observed several times this week during periods of clear weather and light cloud-cover. Intermittent low-level seismicity characterized by occasional low frequency earthquakes was detected during week. The level of unrest observed over the past several weeks indicates that eruptive activity has paused or stopped. Pauses in eruptive activity are common at Veniaminof. Lava effusion, ash emissions, or both could resume at any time without significant associated seismicity.

Veniaminof volcano is monitored with a local real-time seismic network, which will typically allow AVO to detect changes in unrest that may lead to a more significant explosive eruption. AVO combines seismic, infrasound, lightning, and satellite data for rapid detection of such events.

Mount Veniaminof volcano is an andesitic stratovolcano with an ice-filled 10-km diameter summit caldera located on the Alaska Peninsula, 775 km (480 mi) southwest of Anchorage and 35 km (22 mi) north of Perryville. Veniaminof is one of the largest (~300 cubic km; 77 cubic mi) and most active volcanic centers in the Aleutian Arc and has erupted at least 13 times in the past 200 years. Recent significant eruptions of the volcano occurred in 1993-95, 2005, and 2013. These were Strombolian eruptions that produced lava fountains and minor emissions of ash and gas from the main intracaldera cone. During the 1993-95 activity, a small lava flow was extruded, and in 2013, five small lava flows effused from the intracaldera cone over about five months. Minor ash-producing explosions occurred nearly annually between 2002 and 2010. Previous historical eruptions have produced ash plumes that reached 20,000 ft above sea level (1939 and 1956) and ash fallout that blanketed areas within about 40 km (25 mi) of the volcano (1939).

52°49'20" N 169°56'42" W, Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Elevated surface temperatures at the summit of the volcano were observed occasionally in satellite images throughout the week. No explosive activity was detected in regional seismic or infrasound data during the week. Satellite views showed continued slow subsidence of the lava dome with no evidence of new lava.

The most recent explosion of Cleveland occurred on January 9, 2019. Cleveland explosions 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 less likely and/or frequent.

Local seismic and infrasound data at Cleveland have been offline since January 26, which restricts AVO's ability to rapidly detect an explosive eruption. AVO continues monitoring for signs of eruptive activity with satellite, lightning, and regional seismic and infrasound 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.


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

David Fee, Coordinating Scientist, UAFGI
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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