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USGS Volcano Notice - DOI-USGS-AVO-2023-05-18T20:06:37-08:00

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ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, May 19, 2023, 12:17 PM AKDT (Friday, May 19, 2023, 20:17 UTC)


GREAT SITKIN (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

Lava continued to slowly erupt at Great Sitkin over the past week, adding to a thick lava flow confined to the summit crater. Satellite images through May 16 showed that the lava flow is growing mainly to the east into the summit crater ice field. Only a few small local earthquakes were detected at Great Sitkin during the week. No other noteworthy activity was observed in cloud-obscured views of the volcano in satellite and web camera data.   

Great Sitkin is monitored by local seismic and infrasound sensors, satellite data, web cameras, and regional infrasound and lightning networks. 



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 26 miles (43 km) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a ~1 mile (1.5 km)-diameter summit crater. A steep-sided lava dome, emplaced during the 1974 eruption, occupies the center of the crater. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft (7.6 km) 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.



SEMISOPOCHNOI (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

The level of activity at Semisopochnoi has declined over the past week. The last evidence of ash emissions from the volcano was on May 5 and consisted of a light dusting of ash on the northwest flank of the north crater of Mount Young. The Aviation Color Code and Volcano Alert Level were lowered to YELLOW/ADVISORY on Wednesday, May 17. Low-level steaming from the north crater of Mount Young continues to be observed in webcam images and seismicity remains slightly elevated.   

Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Young, and ash clouds usually under 10,000 ft (3 km) above sea level, have characterized the recent eruptive activity. Additional ash-producing events could occur again with little warning.     

Semisopochnoi volcano is monitored by local seismic and infrasound sensors, satellite data, web cameras, and regional infrasound and lightning networks.  



Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by a 5-mile (8 km) diameter caldera that contains a small lake and several post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. Prior to 2018, the previous known historical eruption of Semisopochnoi volcano 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 Young, a three-peaked cone cluster in the southwest part of the caldera. Mount Young has been intermittently active since 2018. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 40 miles (65 km) northeast of Amchitka Island and 130 miles (200 km) west of Adak.



ANIAKCHAK (VNUM #312090)
56°54'21" N 158°12'32" W, Summit Elevation 4400 ft (1341 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Earthquake activity beneath Aniakchak volcano remained above background levels over the past week. The earthquakes are occurring below the center of the caldera and to the east of the volcano at depths shallower than about 4 miles (6 km). No other signs of volcanic unrest were observed in satellite or webcam images over the last week, and no new satellite radar data of ground movement were available.   

Increases in seismic activity and ground movement have been detected previously at other similar volcanoes, with no subsequent eruptions. We expect additional shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in ground movement to precede any future eruption, if one were to occur.  

AVO monitors Aniakchak with a local network, which consists of six seismometers, a web camera, and a single infrasound sensor, as well as satellite remote sensing data and regional infrasound and lightning networks. Several of the seismic stations, however, stopped transmitting data on March 4 due to low power levels. Another seismometer on the volcano stopped transmitting data on April 21 due to presumed snow cover and low power levels. A new seismometer was installed in Port Heiden on April 12, so two local seismic stations are now in operation. We are unable to locate smaller earthquakes due to the outages. A new webcam was also deployed in Port Heiden. 



Aniakchak volcano, located in the central portion of the Alaska Peninsula, consists of a stratovolcano edifice with a 6 miles (10 km) diameter summit caldera. The caldera-forming eruption occurred around 3,500 years ago. Postcaldera eruptions have produced lava domes, tuff cones, and larger spatter and scoria cone structures including Half-Cone and Vent Mountain all within the caldera. The most recent eruption occurred in 1931 and created a new vent and lava flows on the western caldera floor while spreading ash over much of southwestern Alaska. Aniakchak volcano is 15 miles (25 km) southeast of the nearest community, Port Heiden, and 416 miles (670 km) southwest of Anchorage, Alaska.



TAKAWANGHA (VNUM #311090)
51°52'1" N 178°1'37" W, Summit Elevation 4754 ft (1449 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Earthquake activity beneath Takawangha volcano, which began in the fall of 2022 and peaked on March 9–11, continued over the past week. The number of earthquakes located each day beneath Tanaga Island varied but continued at an overall rate similar to previous weeks. Most recent earthquakes locate between Takawangha volcano and nearby Tanaga Volcano, about 5 miles (8 km) west of Takawangha volcano on Tanaga Island. 

No other signs of volcanic unrest were observed in satellite data over the last week, and no new satellite radar data were available to verify if recent ground movement has continued.  

Because seismic activity is also elevated at nearby Tanaga Volcano, if an eruption were to occur, it is unclear at this stage whether it would come from Tanaga Volcano or Takawangha volcano.  

An increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in ground movement, will likely precede any eruption if one were to occur.  

Takawangha is monitored with a local seismic network, a single local infrasound sensor, regional infrasound and lightning sensors, and satellite imagery.  



Takawangha is a remote, 4,754 ft (1,449 m)-high stratovolcano located on the northeast portion of Tanaga Island, roughly 59 miles (95 km) west of Adak in the Andreanof Islands. Takawangha's summit is mostly ice-covered, except for four young craters that have erupted ash and lava flows in the last few thousand years. Parts of Takawangha's edifice are hydrothermally altered and may be unstable, possibly leading to localized debris avalanches from its flanks. Takawangha lies across a saddle from historically active Tanaga volcano to the west. No historical eruptions are known from Takawangha; however, field work shows that recent eruptions have occurred, and it is possible that historic eruptions attributed to Tanaga may instead have come from Takawangha.



TRIDENT (VNUM #312160)
58°14'3" N 155°6'9" W, Summit Elevation 3599 ft (1097 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Seismicity beneath Trident Volcano remained above background levels over the last week. A magnitude 4.0 shallow earthquake occurred on Friday, May 12 that was located about 3 miles (4 km) west of Trident Volcano.  Earthquake activity was quieter early in the week but briefly increased again on Wednesday and Thursday, May 18 and 19. No eruptive activity or other signs of unrest were reported in satellite or web camera views.  

The current period of seismic unrest began on August 24, 2022. Earthquake depths at the beginning of the swarm were mainly deep, around 16 miles (25 km) below sea level and became progressively shallower to around 3 miles (5 km) over the following four days. Since late August 2022, most earthquakes have occurred within the shallow crust, with depths less than 4 miles (6 km) below sea level.  

Increases in seismic activity have been detected previously at Trident Volcano and other similar volcanoes, with no subsequent eruptions. We expect additional shallow seismicity and other signs of unrest, such as gas emissions, elevated surface temperatures, and ground movement, to precede any future eruption if one were to occur.   

AVO monitors Trident Volcano with a local network of seismometers, a webcam, remote sensing data, and regional infrasound and lightning networks.



Trident is one of the Katmai group of volcanoes located within Katmai National Park and Preserve on the Alaska Peninsula. Trident consists of a complex of four cones and numerous lava domes, all andesite and dacite in composition, that reach as high as 6,115 ft (1,864 m) above sea level. An eruption beginning in 1953 constructed the newest cone, Southwest Trident, and four lava flows on the flank of the older complex. This eruption continued through 1974 and produced ash (an initial plume rose to 30,000 ft or 9 km asl), bombs, and lava at various times. Fumaroles remain active on the summit of Southwest Trident and on the southeast flank of the oldest, central cone. Trident is located 92 miles (148 km) southeast of King Salmon and 273 miles (440 km) southwest of Anchorage.



TANAGA (VNUM #311080)
51°53'2" N 178°8'35" W, Summit Elevation 5925 ft (1806 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Earthquake activity near Tanaga Volcano, which began in the fall of 2022 and peaked on March 9–11, continued over the past week. The number of earthquakes located each day beneath Tanaga Island varied but continued at an overall rate similar to previous weeks. Most recent earthquakes are between Tanaga Volcano and nearby Takawangha volcano, which is about 5 miles (8 km) east of Tanaga Volcano on Tanaga Island.

No other signs of volcanic unrest were observed in satellite data over the last week, and no new satellite radar data were available to verify if recent ground movement has continued.  

Because the seismic activity is also elevated at nearby Takawangha volcano, if an eruption were to occur, it is unclear at this stage whether it would come from Tanaga Volcano or Takawangha volcano.  

An increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in ground movement, will likely precede any eruption if one were to occur.  

Tanaga is monitored with a local seismic network, a single local infrasound sensor, regional infrasound and lightning sensors, and satellite imagery.  



Tanaga Island lies in the Andreanof Islands approximately 62 miles (100 km) west of the community of Adak and 1260 miles (2025 km) SW of Anchorage. The northern half of the island is home to the Tanaga volcanic complex, comprising three main volcanic edifices. Tanaga Volcano is the tallest of these (5,925 ft or 1,806 m) and lies in the center of the complex. The last reported eruption of Tanaga occurred in 1914 and earlier eruptions were reported in 1763-1770, 1791, and 1829. Reports of these eruptions are vague, but deposits on the flanks of the volcano show that typical eruptions produce blocky lava flows and occasional ash clouds. Eruptions have occurred both from the summit vent and a 5,197 ft (1,584 m)-high satellite vent on the volcano's northeast flank. Immediately west of Tanaga volcano lies Sajaka, a 4,443 ft (1,354 m)-high compound edifice with an older cone to the east that collapsed into the sea within the last few thousand years, and a new cone that has grown in the breach. The new cone is 4,305 ft (1,312 m) high and consists of steeply dipping, interbedded cinders and thin, spatter-fed lava flows. To the east of Tanaga lies Takawangha, which is separated from the other active volcanic vents by a ridge of older rock. No historical eruptions are known from Sajaka or Takawangha; however, field work shows that recent eruptions have occurred, and it is possible that historic eruptions attributed only to Tanaga may instead have come from these other vents. 





CONTACT INFORMATION:

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

David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (907) 378-5460



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.