USGS Volcano Notice - DOI-USGS-AVO-2023-07-23T13:15:17-08:00

Eruption activity increased throughout yesterday with rising seismic tremor and surface temperatures reflecting lava activity at the summit crater. Sulfur dioxide degassing was detected in satellite data midday. The increasing activity led to a VAN/VONA issued at 4:53 pm AKDT (00:43 on July 23 UTC) warning of the possibly of increasing ash emission in the next few hours.

Passing airplanes first reported low-level ash plumes around 7:00 pm AKDT (03:00 on July 23 UTC). At 11:20 pm AKDT (07:20 on July 23 UTC) satellite images began indicating growth of a significantly higher ash plume, eventually reaching 37,000 ft. (11 km) above sea level. In response, the Aviation Color Code was raised to RED and the Volcano Alert Level was raised to WARNING.

Seismic activity began rapidly declining at 1:09 am on July 23 (09:09 UTC) and active ash emissions were no longer visible in satellite data at 1:30 am (09:30 UTC). Bursts of increased seismicity were recorded throughout the morning but overall remained at low levels. Elevated surface temperatures were indicated in satellite data until 6:00 am (14:20 UTC). In response to decreasing activity the Aviation Color Code was reduced to ORANGE and the Volcano Alert Level was reduced to WATCH.

This was the fourth period of elevated eruptive activity resulting in significant ash plumes during the current eruption. It is unknown how long this eruption will last, but previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of activity similar to those seen in the last two weeks.

Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. The local monitoring network has been partially impaired over the last few weeks due to telecommunications issues but seismic stations and web cameras south of the volcano were brought back online on July 19. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.

Slow eruption of lava continues at Great Sitkin Volcano, where it is producing a thick lava flow within the summit crater. A high-resolution satellite images showed steaming of the lava flow surface over the vent area.  Earthquake activity remains slightly elevated. Around 20 small earthquakes were detected over the past day on local instruments.

The current lava flow at Great Sitkin Volcano began erupting in July 2021. No explosive events have occurred since a single event in May 2021.

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

Around 13 small local earthquakes were detected at Cleveland volcano over the last day, although many of these are too small to locate. Cloudy conditions obscured views of the volcano in satellite and web camera images.

Episodes of lava effusion and explosions can occur without advance warning. Explosions from Mount 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.

Cleveland volcano is currently monitored with a five-station real-time seismic network and three nearby web cameras. Based on past events, explosive eruptions of Cleveland may occur with little or no warning. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, web camera, lightning, and satellite data.

Seismic activity near Trident Volcano remained elevated over the past 24 hours. No volcanic activity or unrest was observed in clear satellite and web camera images over the past day. 

The current period of seismic unrest began on August 24, 2022. Increases in seismic activity have been detected previously at Trident Volcano and other similar volcanoes and did not result in 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.     

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

Seismicity was low at Aniakchak volcano over the past day with 4 local earthquakes detected. No activity was observed in web camera images over the past 24 hours.

The current period of seismic unrest began in October 2022. Increases in seismic activity have been detected previously at 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 additional surface deformation to precede any future eruption, if one were to occur.

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

Six minor earthquakes were detected over the last day at Semisopochnoi Island. Clouds obscured all satellite and web camera images.

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 recent periods of eruption since 2018. The last evidence of ash emission from the volcano was on May 5, 2023, and consisted of a minor dusting of ash on the northwest flank of the north crater of Mount Young. Additional ash-producing events could occur again with little or no warning. 

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