ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, November 30, 2018, 1:00 PM AKST (Friday, November 30, 2018, 22:00 UTC)

VENIAMINOF VOLCANO (VNUM #312070)
56°11'52" N 159°23'35" W, Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Effusion of lava and minor ash and steam emissions continue from the intracaldera cone at Veniaminof volcano. Low-level continuous seismic tremor has been recorded all week, and several small explosions were detected from regional infrasound arrays. Elevated thermal signatures were observed in satellite images throughout the week, and clear nighttime webcam images showed incandescence. Minor ash and steam emissions were also observed in satellite and daytime webcam imagery. Trace ashfall is still possible in nearby communities.

The Veniaminof seismic network went offline following this morning's M 7.0 earthquake in Anchorage. It is unclear when the data from the seismic network will be restored. The volcano continues to be monitored with regional infrasound arrays and satellite observations.

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).

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

No eruptive activity was observed in satellite imagery or regional infrasound over the past week.

The satellite link that transmits seismic data from Semisopochnoi failed on November 1, but an infrasound array on Adak Island should detect significant explosive emissions from Semisopochnoi (with a 13-minute delay) if atmospheric conditions permit. Planning is underway to visit Amchitka Island in order to make repairs to the satellite facility that transmits Semisopochnoi data, weather permitting.

A return to eruptive activity remains a possibility at Semisopochnoi and it could occur with little or no warning. AVO will continue to monitor the volcano closely. Semisopochnoi is normally monitored with an on-island seismic network, the infrasound array on Adak Island, and remotely by satellite and lightning sensors.

Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and a number of post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. The last known eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking. Another prominent, young post-caldera landform is Mount Cerberus, a three-peaked cone cluster in the southwest part of the caldera. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak.

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

Nothing significant was detected in seismic or infrasound (pressure) sensor data this week. There were no observations of activity in mostly cloudy satellite images.

Future explosive activity is likely and would occur without warning. Previous explosions have produced hazardous conditions primarily near the volcano, but occasionally they have been large enough to produce a drifting ash cloud.

Cleveland volcano is monitored by only two seismic stations, which restricts 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. The local web camera, one seismic station, and the local infrasound array are offline due to an equipment failure on September 23rd. This hampers efforts to rapidly detect explosive activity; however, Cleveland remains monitored with a single seismic station and regional instruments.

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.

GREAT SITKIN VOLCANO (VNUM #311120)
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 continues at Great Sitkin Volcano. Seismicity remains elevated with small earthquakes occurring at rates above background levels. No other activity was observed in partly cloudy to mostly cloudy satellite images or regional infrasound data over the past week.

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.

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:

Dave Schneider, Acting Scientist-in-Charge, USGS
djschneider@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAFGI
jflarsen@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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